Evolution of intermolecular contacts with temperature and pressure in bromoethane and iodo­ethane – a comparative study

Bujak, M.; Olejniczak, A.; Podsiadło, M.

doi:10.1107/S2052520622010149

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ISSN: 2052-5206

Volume 78| Part 6| December 2022| Pages 868-875

https://doi.org/10.1107/S2052520622010149

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Evolution of intermolecular contacts with temperature and pressure in bromoethane and iodoethane – a comparative study

Maciej Bujak,^a ^* Anna Olejniczak ^b and Marcin Podsiadło ^b ^*

^aFaculty of Chemistry, University of Opole, Oleska 48, Opole, 45-052, Poland, and ^bFaculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8, Poznań, 61-614, Poland
^*Correspondence e-mail: mbujak@uni.opole.pl, marcinp@amu.edu.pl

Edited by A. Nangia, CSIR–National Chemical Laboratory, India (Received 13 July 2022; accepted 19 October 2022; online 9 November 2022)

At ambient conditions two liquids, bromoethane, C₂H₅Br (MBE, m.p. 154.6 K) and iodoethane, C₂H₅I (MIE, m.p. 162.1 K), have been crystallized under both isobaric and isochoric conditions using in situ low-temperature and high-pressure techniques. The single-crystal X-ray diffraction studies, supported by the isothermal compressibility and isobaric differential scanning calorimetry measurements, allowed the monitoring and analysis at low temperature and high pressure of the effects of externally induced changes in MBE and MIE. The monoclinic MBE and MIE crystals are found to be isostructural. They are stable, in the investigated regimes, i.e. down to 100 K/0.1 MPa and up to ∼295 K/3.7 GPa, without undergoing any symmetry or phase change. Both the contraction and compression is mainly noted for the intermolecular separation distances. The Hirshfeld surface analysis of intermolecular contacts clearly shows the nature of occurrence and hierarchy of interactions pointing out the role played by Br/I⋯Br/I contacts, in particular at ambient temperature and high-pressure conditions. The preferences for the formation of intermolecular contacts in MIE are more pronounced and do not require such extreme conditions as in the case of MBE. It is notable that the Br/I⋯Br/I and Br/I⋯H contacts could be basically classified as type-I interactions.

Keywords: in situ crystallization; low temperature; high pressure; halogenated alkanes.

CCDC references: 2213873; 2213874; 2213875; 2213876; 2213877; 2213878; 2213879; 2213880; 2213881; 2213882; 2213883; 2213884; 2213885; 2213886

1. Introduction

The in situ low-temperature and high-pressure experimental techniques of structural chemistry are successfully used in investigations of compounds that are liquids or gases at ambient conditions. Both these techniques have been relatively easily implemented into X-ray diffraction studies to investigate the limited factors that are usually not available at ambient conditions, including weak intermolecular interactions, polymorphism and structural transformations (e.g. Brodalla et al., 1985 ; Goeta & Howard, 2004 ; Kirchner et al., 2010 ; Bujak & Katrusiak, 2010 ; Boese, 2014 ; Maloney et al., 2014 ; Li et al., 2016 ; Dey et al., 2019 ; Boldyreva, 2019 ; Katrusiak, 2019 ). The first issue, associated with intermolecular interactions, relates to both structural transformations of materials and the products of those changes – different phases and polymorphic forms that could be induced by applying external temperature or pressure. It is also worth noting that variations in those physicochemical crystallization parameters effectively affect the structure and properties of the solid-state products that are obtained. These apply to crystallization of new compounds as well as new forms of known compounds including their cocrystals. The X-ray diffraction studies, besides the changes of geometrical parameters, can also indicate the importance and energy of the specific interactions responsible for the unique behaviour of a given crystalline material.

The relatively small, and preferably showing well defined types of interactions, alkanes and their derivatives could be considered as the model compounds for the studies of molecular materials at non-ambient conditions (e.g. Boese et al., 1999 ; Dziubek et al., 2009 ; Bujak et al., 2019 ). The previous investigations on the whole group of chloroethanes clearly showed the differences within their isomers arising from the different nature of intermolecular interactions. 1,2-Dichloroethane (12DCE), in contrast to its asymmetrically substituted isomeric 1,1-dichloroethane (11DCE) shows Cl⋯Cl contacts within a regime of the sum of the van der Waals radii (Boese et al., 1992 ; Bujak et al., 2004 , 2008a ; Bondi, 1964 ). Similar behaviour was found for trichloroethanes, i.e. 1,1,2- and the more asymmetrically substituted 1,1,1-trichloroethane (Bujak et al., 2008b ; Bujak et al., 2011 ). Therefore both 11DCE and 111TCE could be considered as `crystalline gases' with no intermolecular interactions shorter than the sums of the van der Waals radii of respective atoms. In these crystals, the lack of interactions between asymmetrically substituted ethane molecules could be explained in terms of the specific shape of molecules that, in turn, is related to both the mismatch of electrostatic potential on the surfaces of molecules and also steric hindrances.

The simplest among chloroethanes (mono)chloroethane (C₂H₅Cl, MCE) has been found to crystallize in two different phases depending on the crystallization conditions (Podsiadło et al., 2012 ). The low-temperature isobaric freezing resulted in the monoclinic P2₁/n phase I, whereas the high-pressure crystallization, at isochoric conditions, yielded the hexagonal P6₃/m phase II. Besides the differences associated with crystal symmetry and structure, the main dissimilarity between these two phases relates to intermolecular interactions. The low-temperature monoclinic phase I, similar to aforementioned 11DCE and 111TCE, shows no intermolecular contacts within the sums of the van der Waals radii regime, whereas in the high-pressure hexagonal phase II the chloroethane molecules are joined together by all possibly expected Cl⋯Cl, Cl⋯H and H⋯H interactions.

Herein, continuing our studies on simple compounds under extreme conditions, we present our structural investigations on two analogous halogenoethanes: (mono)bromoethane, C₂H₅Br (MBE) and (mono)iodoethane, C₂H₅I, (MIE). Similar to MCE, MBE and MIE are liquids under ambient conditions (Lide, 2007 ). Both MBE and MIE have been in situ crystallized at low-temperature and high-pressure conditions, and subsequently their single-crystal structures have been determined at various low-temperature ambient-pressure and ambient-temperature high-pressure points. The X-ray diffraction studies have been supported by ambient-temperature compressibility and thermoanalytical ambient-pressure differential scanning calorimetry measurements. To further understand and compare the processes occurring with halogen atom exchange as well as the influence of decreasing temperature and increasing pressure on the formation and nature of interactions, in these two simple alkane derivatives, Hirshfeld surface analysis of intermolecular contacts has been applied.

2. Experimental

Bromoethane, C₂H₅Br (MBE) and iodoethane, C₂H₅I (MIE) (both ReagentPlus, 99%, Sigma-Aldrich) were used directly, as commercially supplied, in the single-crystal X-ray diffraction, compressibility and differential scanning calorimetry experiments.

2.1. In situ low-temperature crystallization

The colourless liquid samples of MBE and MIE were sealed in thin-walled glass capillaries (internal diameter of 0.3 mm and wall of 0.01 mm thickness) and mounted on a diffractometer. The temperature was controlled by an Oxford Cryosystems Cryostream cooler. The samples initially froze as the polycrystalline materials. Then, the reduction of the number of crystal seeds, by cycling the temperature close to melting points of those compounds (Lide, 2007) followed by slow temperature decrease, allowed for the growth of sufficiently large single crystals used for the collection of X-ray diffraction data.

2.2. In situ high-pressure crystallization

The high-pressure experiments of MBE and MIE were performed using a modified Merrill–Bassett diamond-anvil cell (DAC) (Merrill & Bassett, 1974 ; Bassett, 2009 ). The diameter of the diamond culets was 0.8 mm. The gasket was made of 0.1 mm (MBE) and 0.3 mm (MIE) thick steel foil with a spark-eroded hole of 0.4 mm in diameter for both MBE and MIE (Katrusiak, 1999 ). The ruby-fluorescence method, using a BETSA PRL spectrometer, was utilized to measure the pressure in the DAC (Barnett et al., 1973 ; Piermarini et al., 1975 ) with the accuracy of ∼0.02 GPa.

Several attempts to crystallize MBE and MIE were undertaken. Eventually, the best results were obtained for initial squeezing of the liquid samples, up to ∼2 GPa in the DAC, followed by quenching the DAC (with a non-solidified sample) in liquid nitrogen. This resulted in the polycrystalline MBE and MIE samples being obtained. Then the DAC, with the polycrystalline sample, was allowed to reach room temperature. The single crystals of both MBE and MIE were obtained under isochoric conditions: the DAC with the polycrystalline material was heated using a hot-air gun until all but one crystal seed were melted. In the next step the single crystal grew, as the DAC was cooled slowly to ambient temperature in a controlled manner, and eventually the sample filled the whole volume of the high-pressure chamber. The progress in growing of the single-crystal samples, at selected high-pressure points, of MBE and MIE is shown in Figs. 1, S1 and S2 (in the supporting information). For all high-pressure experiments, except of those for MBE at 3.07 (2) and 3.87 (2) GPa (in which the single-crystal sample previously obtained at 2.13 (2) GPa was slowly pressurized), after the data collection processes, the pressure in the DAC was increased and the crystals were melted. Then the `new' single-crystal samples were isochorically grown again at higher pressure.

Figure 1
Stages of isochoric, with decreasing temperature, growth of the MBE (a)–(c) and MIE (d)–(f) single crystals in a diamond-anvil cell (cf. Figs. S1 and S2).

2.3. Data collection, data reduction, structure solution and refinement

The various-temperature ambient-pressure (0.1 MPa) and room-temperature [295 (2) K] high-pressure diffraction data were collected on a KUMA KM4-CCD diffractometer with an Eos detector (variable temperature for MBE, and variable pressure for MBE and MIE) and on an Xcalibur Eos diffractometer (variable temperatures for MIE), both with the graphite-monochromated Mo Kα radiation.

The first low-temperature datasets, for both MBE and MIE, were gathered at the same highest possible temperature, limited by the stability of the single-crystal samples, i.e. at 140.0 (1) K. Then the temperature of the crystal samples was slowly decreased and the diffraction data were collected at 120.0 (1) and 100.0 (1) K. For both MBE and MIE the reflections were measured using the ω-scan technique with Δω = 1.0° and Δt = 5 s exposure time.

The single-crystal samples of both MBE and MIE, pressurized in a DAC, were centred on a diffractometer using the shadow method (Budzianowski & Katrusiak, 2004 ). The first datasets were collected at a very similar pressure value ensuring the stability of the crystal samples during data collection processes, i.e. 1.83 (2) and 1.88 (2) GPa for MBE and MIE, respectively. Then the pressure was increased in three, on average, ∼0.6 GPa steps finally reaching 3.87 (2) and 3.62 (2) GPa for MBE and MIE, respectively. The room-temperature high-pressure intensity data were collected using the ω- and φ-scan techniques with Δω/Δφ = 0.75°. The exposure time was 25 and 35 s for MBE and MIE, respectively.

The CrysAlisPro program was used for the data collection, unit-cell refinement and data reduction (Rigaku Oxford Diffraction, 2015 $[Rigaku Oxford Diffraction (2015). CrysAlisPro. Rigaku Corporation, The Woodlands, TX, USA.]$ , 2020 $[Rigaku Oxford Diffraction (2020). CrysAlisPro. Rigaku Corporation, The Woodlands, TX, USA.]$ ). All data were corrected for Lorentz, polarization and absorption effects (Rigaku Oxford Diffraction, 2020 $[Rigaku Oxford Diffraction (2020). CrysAlisPro. Rigaku Corporation, The Woodlands, TX, USA.]$ ). The structures were solved by direct methods and refined with SHELX (Sheldrick, 2008 , 2015 ). All C, Br and I atoms were refined with anisotropic displacement parameters. The comparison of the average ADP values for non-H atoms of MBE and MIE as well as unit-volume changes with temperature and pressure are depicted in Fig. S3. H-atom positions in all structures were located in difference Fourier maps and then a riding model was applied. The isotropic displacement parameters of the H atoms were fixed to 1.2 and 1.5U_eq of their carrier C atoms.

The asymmetric units and the labelling of C, Br and I atoms for both MBE and MIE, at all studied low-temperature and high-pressure points, were chosen in the same manner to show the structural relationship between the positions of corresponding atoms and intermolecular contacts as well as to the previously investigated monoclinic phase I of MCE (Podsiadło et al., 2012).

The crystal data and structure determination summary for MBE and MIE at all low-temperature and high-pressure conditions are listed in Tables 1, 2 and S1–S4 (in the supporting information). The coefficients of thermal expansion and compressibility along with the Birch–Murnaghan coefficients, calculated using PASCal (Cliffe & Goodwin, 2012 ), are given in Tables S5–S8. The bond lengths, bond angles and the geometries of shortest intermolecular contacts are presented in Tables 3, 4 and S9–S14. Intermolecular contacts were compared using Hirshfeld surface analysis with CrystalExplorer17 (Turner et al., 2017 ; Spackman et al., 2021 ). The structures were drawn using Mercury (Macrae et al., 2020 ).

Table 1
Selected crystal data for MBE at various temperature and pressure conditions

For all experiments: C₂H₅Br, M_r = 108.96, monoclinic crystal system, space group P2₁/n and Z = 4.

Temperature	140.0 (1) K	120.0 (1) K	100.0 (1) K	295 (2) K	295 (2) K	295 (2) K	295 (2) K
Pressure	0.1 MPa	0.1 MPa	0.1 MPa	1.83 (2) GPa	2.13 (2) GPa	3.07 (2) GPa	3.87 (2) GPa
a (Å)	5.5329 (5)	5.5204 (5)	5.5087 (4)	5.2831 (6)	5.2524 (6)	5.1730 (8)	5.107 (3)
b (Å)	9.9018 (10)	9.8941 (8)	9.8814 (8)	9.4910 (9)	9.4479 (12)	9.3305 (18)	9.206 (7)
c (Å)	7.0147 (7)	6.9655 (6)	6.9315 (6)	6.5957 (6)	6.5350 (6)	6.3822 (9)	6.285 (3)
β (°)	100.309 (9)	100.340 (9)	100.379 (8)	100.623 (11)	100.664 (10)	100.777 (17)	101.08 (6)
V (Å³)	378.10 (6)	374.27 (6)	371.13 (5)	325.05 (6)	318.69 (6)	302.61 (9)	290.0 (3)
R[F² > 2σ(F²)]	0.0211	0.0220	0.0211	0.0163	0.0189	0.0314	0.0584
wR(F²)	0.0433	0.0506	0.0484	0.0425	0.0521	0.0892	0.1346

Table 2
Selected crystal data for MIE at various temperature and pressure conditions

For all experiments: C₂H₅I, M_r = 155.96, monoclinic crystal system, space group P2₁/n and Z = 4.

Temperature	140.0 (1) K	120.0 (1) K	100.0 (1) K	295 (2) K	295 (2) K	295 (2) K	295 (2) K
Pressure	0.1 MPa	0.1 MPa	0.1 MPa	1.88 (2) GPa	2.40 (2) GPa	3.18 (2) GPa	3.62 (2) GPa
a (Å)	5.85463 (16)	5.83962 (16)	5.82719 (15)	5.5767 (13)	5.5292 (9)	5.4696 (8)	5.4335 (11)
b (Å)	10.1532 (3)	10.1442 (3)	10.1348 (2)	9.7073 (6)	9.6336 (7)	9.5403 (6)	9.4863 (7)
c (Å)	7.2722 (2)	7.2368 (2)	7.2028 (2)	6.8424 (3)	6.7597 (2)	6.6492 (6)	6.5840 (4)
β (°)	102.701 (3)	102.705 (3)	102.711 (3)	102.262 (10)	102.209 (8)	102.280 (13)	102.191 (12)
V (Å³)	421.71 (2)	418.20 (2)	414.96 (2)	361.96 (9)	351.92 (6)	339.03 (6)	331.71 (8)
R[F² > 2σ(F²)]	0.0119	0.0115	0.0110	0.0256	0.0375	0.0352	0.0263
wR(F²)	0.0272	0.0254	0.0231	0.0685	0.1378	0.0969	0.0700

Table 3
Dimensions (Å, °) of the shortest intermolecular contacts Br⋯Br and Br⋯H for MBE at various temperature and pressure conditions, compared to those commensurate with the sums of the van der Waals radii of respective atoms at 295 (2) K/3.87 (2) GPa

Temperature	140.0 (1) K	120.0 (1) K	100.0 (1) K	295 (2) K	295 (2) K	295 (2) K	295 (2) K
Pressure	0.1 MPa	0.1 MPa	0.1 MPa	1.83 (2) GPa	2.13 (2) GPa	3.07 (2) GPa	3.87 (2) GPa
Br1⋯Br1ⁱ	3.8860 (7)	3.8458 (6)	3.8155 (6)	3.6040 (9)	3.5606 (8)	3.465 (2)	3.393 (5)
C1—Br1⋯Br1ⁱ	156.63 (8)	157.40 (8)	157.79 (8)	157.91 (11)	158.13 (10)	159.3 (3)	161.4 (5)
Br1⋯Br1ⁱ—C1ⁱ	156.63 (8)	157.40 (8)	157.79 (8)	157.91 (11)	158.13 (10)	159.3 (3)	161.4 (5)
Br1⋯H11ⁱⁱ	3.24	3.24	3.23	3.05	3.02	2.96	2.96
C1—Br1⋯H11ⁱⁱ	139	138	138	135	134	133	132
Br1⋯H11ⁱⁱ–C1ⁱⁱ	136	136	136	136	136	136	132
Br1⋯H12ⁱⁱⁱ	3.37	3.33	3.31	3.11	3.08	3.01	2.97
C1—Br1⋯H12ⁱⁱⁱ	91	91	91	90	90	89	91
Br1⋯H12ⁱⁱⁱ—C1ⁱⁱⁱ	138	138	138	137	137	135	134
Br1⋯H22^iv	3.30	3.27	3.25	3.06	3.04	3.02	3.05
C1—Br1⋯H22^iv	109	109	109	113	112	111	106
Br1⋯H22^iv—C2^iv	138	139	138	141	140	135	124
Br1⋯H23^v	3.14	3.14	3.14	2.99	2.95	2.84	2.83
C1—Br1⋯H23^v	135	134	133	132	133	134	137
Br1⋯H23^v—C2^v	163	160	160	151	155	162	165
Symmetry codes: (i) 1 − x, 2 − y, 2 − z; (ii) 1 + x, y, z; (iii) ½ + x, $[3\over 2]$ − y, ½ + z; (iv) −x, 2 − y, 2 − z; (v) ½ − x, ½ + y, $[3\over 2]$ − z.

Table 4
Dimensions (Å, °) of the shortest intermolecular contacts I⋯I and I⋯H for MIE at various temperature and pressure conditions, compared to those commensurate with the sums of the van der Waals radii of respective atoms at 295 (2) K/3.62 (2) GPa

Temperature	140.0 (1) K	120.0 (1) K	100.0 (1) K	295 (2) K	295 (2) K	295 (2) K	295 (2) K
Pressure	0.1 MPa	0.1 MPa	0.1 MPa	1.88 (2) GPa	2.40 (2) GPa	3.18 (2) GPa	3.62 (2) GPa
I1⋯I1ⁱ	4.0008 (3)	3.9770 (3)	3.9564 (3)	3.7574 (13)	3.7072 (18)	3.639 (2)	3.6061 (15)
C1—I1⋯I1ⁱ	154.22 (6)	154.63 (5)	154.93 (5)	154.62 (15)	154.9 (3)	155.5 (3)	155.5 (2)
I1⋯I1ⁱ—C1ⁱ	154.22 (6)	154.63 (5)	154.93 (5)	154.62 (15)	154.9 (3)	155.5 (3)	155.5 (2)
I1⋯H11ⁱⁱ	3.39	3.38	3.37	3.17	3.16	3.08	3.06
C1—I1⋯H11ⁱⁱ	138	138	137	134	134	133	132
I1⋯H11ⁱⁱ—C1ⁱⁱ	138	138	138	138	138	138	138
I1⋯H12ⁱⁱⁱ	3.39	3.37	3.35	3.13	3.09	3.03	2.99
C1—I1⋯H12ⁱⁱⁱ	87	87	87	86	86	86	86
I1⋯H12ⁱⁱⁱ—C1ⁱⁱⁱ	142	142	142	142	141	141	141
I1⋯H22^iv	3.42	3.40	3.39	3.19	3.15	3.13	3.08
C1—I1⋯H22^iv	108	108	108	111	112	110	112
I1⋯H22^iv—C2^iv	140	140	140	141	142	137	140
I1⋯H23^v	3.31	3.30	3.29	3.09	3.06	2.99	2.98
C1—I1⋯H23^v	139	139	138	139	138	140	138
I1⋯H23^v—C2^v	164	164	164	160	157	165	159
Symmetry codes: (i) 1 − x, 2 − y, 2 − z; (ii) 1 + x, y, z; (iii) ½ + x, $[3\over 2]$ − y, ½ + z; (iv) −x, 2 − y, 2 − z; (v) ½ − x, ½ + y, $[3\over 2]$ − z.

2.4. Differential scanning calorimetry measurements

The ambient-pressure differential scanning calorimetry (DSC) analyses were performed using a DSC8500 (Perkin Elmer) calorimeter with cooling and heating runs of 10 K min⁻¹. Nitrogen (20 ml min⁻¹) was used as a purge gas during the experiments. The measurements were performed in the temperature range 112–298 K only finding characteristic heat anomalies associated with freezing/melting of MBE and MIE. The determined onset temperatures (heating runs) for those phase changes are 153.9 K and 162.9 K for MBE and MIE, respectively (Figs. S4 and S5).

2.5. Compressibility measurements

The room-temperature [295 (2) K] compressibility measurements between ambient pressure and ∼1.1 GPa were performed in the piston-and-cylinder apparatus (Baranowski & Moroz, 1982 ; Dziubek & Katrusiak, 2014 ). The pressure was increased in ∼20–30 MPa steps. The diagrams show no anomalies. The compressibility of both liquids is comparable, however, the larger changes in molecular volume for MIE (30.6 Å³) than for MBE (28.9 Å³) should be noted (Figs. S6 and S7).

3. Results and discussion

The low-temperature and high-pressure single-crystal X-ray diffraction data, for both MBE and MIE, in contrast to MCE (Podsiadło et al., 2012), have revealed only one phase, without any indication of a phase transition or symmetry change from the collected diffraction patterns, in the studied temperature, i.e. down to 100 K/0.1 MPa and pressure i.e. up to ∼295 K/3.7 GPa range. This observation is further confirmed by the low-temperature ambient-pressure differential scanning calorimetry and ambient-temperature high-pressure compressibility measurements showing no anomaly upon decreasing temperature to 112 K/0.1 MPa and compression up to 295 K/1.1 GPa (Figs. S4–S7).

Furthermore, MBE and MIE crystals have been found to be isostructural. The single crystals of both compounds crystallize in monoclinic space group P2₁/n, characterized by the very similar unit-cell parameters along with the positions of corresponding atoms and crystal packing arrangements (Tables 1, 2 and S1–S4, and Fig. 2).

Figure 2
Structures of MBE and MIE at selected low-temperature and high-pressure conditions. MBE at (a) 140 K/0.1 MPa and (b) 295 K/3.87 GPa, MIE at (c) 140 K/0.1 MPa and (d) 295 K/3.62 GPa. The intermolecular space accessible to a probe with a radius of 0.3 Å and grid spacing of 0.2 Å is indicated in yellow. The void volume is (a) 26.5% (100.30 Å³), (b) 5.7% (16.48 Å³), (c) 28.5% (120.40 Å³) and (d) 6.9% (23.02 Å³), respectively. The red dotted lines indicate the intermolecular X⋯X and X⋯H contacts shorter than the sums of the van der Waals radii of respective atoms (X = Br for MBE and X = I for MIE, see Fig. 3

). Displacement ellipsoids are plotted at the 25% probability level.

We have also found that both MBE and MIE behave, in general, in a similar way with decreasing temperature and increasing pressure. All unit-cell parameters decrease, with the exception of the β angle that slightly increases, upon decreasing temperature. The largest linear contraction, of ∼1%, was noted for the c parameters. Overall the unit-cell volumes contract by ∼2% with decreasing temperature from 140 to 100 K. The expected larger changes were found at high pressure. Here, the unit-cell parameters compress, except for the slightly increased β angle in MBE, with increasing pressure from ∼1.9 to ∼3.7 GPa, by ∼4% and ∼10% for the most compressed c parameters and the unit-cell volumes, respectively (Tables 1, 2 and S1–S4). These results are consistent with the calculated coefficients of thermal expansion and compressibility (Tables S5–S8; Cliffe & Goodwin, 2012).

The asymmetric unit of both MBE and MIE contains one crystallographically unique ordered C₂H₅X molecule (X = Br for MBE and X = I for MIE) that adopts a staggered conformation. There are no significant changes in intramolecular bond lengths and angles upon decreasing temperature and increasing pressure – all differences in molecular dimensions are within two e.s.d.s (Tables S9 and S10). As mentioned above, the principal molecular arrangements of structural components in both crystals are similar. However, the patterns of voids, as well as the systems of their intermolecular contacts, show some differences associated with the type of halogen atom and reflecting the hierarchy, number and type of contacts that are present at the specific thermodynamic conditions (Saraswatula & Saha, 2014 ; Saha et al., 2018 ). A somewhat greater volume of voids for MIE than for MBE should be noted. Both the crystal contraction at low temperature and compression upon increasing pressure lead to a decrease of the free space in the crystal structures and the lengths of intermolecular contacts (Fig. 2).

MBE and MIE crystals resemble, in the context of formation and the nature of interactions, the loose-packed crystals of unsymmetrically substituted chloroethanes, including MCE and also hexachloroethane (Bujak et al., 2008a, 2011, 2018 ; Podsiadło et al., 2012). In crystalline MBE and MIE the molecules form X⋯X contacts, which on the basis of their geometrical parameters could be classified as type-I interactions. Considering geometrical criteria for the sums of the van der Waals radii there are no Br⋯Br contacts in any of the low-temperature determined structures of MBE. The first Br⋯Br contacts of 3.6040 (9) Å are noted in the structure determined at 295 K/1.83 GPa. The different behaviour is shown by MIE – lowering temperature at ambient pressure is sufficient to bring the iodoethane molecules to a I⋯I separation distance of 3.9564 (3) Å, at 100 K/0.1 MPa, which is equal to the distance determined for the van der Waals radii regime (3.96 Å, Bondi, 1964). The shortest distances between interacting X atoms have been found at the highest investigated pressure of ∼3.7 GPa. At this pressure both the Br⋯Br and I⋯I contacts are characterized by the separation distances that are, on average, ∼91% of the sums of the van der Waals radii of the respective atoms. To observe X⋯H contacts extreme conditions are needed. The first interactions of this type are observed in the high-pressure structures determined at 295 K/1.83 GPa and 295 K/1.88 GPa for MBE and MIE, respectively. The distances of interacting X and H atoms become closer, upon increasing pressure, and at the highest pressures of ∼3.7 GPa their shortest lengths of 2.83 Å and 2.98 Å for MBE and MIE, respectively, are on average ∼93% of the sums of the van der Waals radii of the respective atoms (Fig. 3, Tables 3, 4, S11 and S12; Bondi, 1964).

Figure 3
Evolution of the selected shortest intermolecular X⋯X and X⋯H distances (X = Br for MBE, and X = I for MIE) with decreasing temperature and increasing pressure for MBE (a, see Table 3

) and MIE (b, see Table 4

). The solid lines are for guiding the eye only. The dotted horizontal lines mark the sums of the van der Waals radii of respective atoms.

The H⋯H interatomic distances, relative to the van der Waals radii, are the longest. The extrapolation of the intermolecular distances up to ∼3.7 GPa shows that most of the shortest H⋯H distances become equal to the sum of the van der Waals radii at ∼3.2 GPa for MBE, whereas in the case of MIE even at the highest pressure of 3.62 GPa, all contacts are somewhat longer than the van der Waals radii regime.

Hirshfeld surface analysis, i.e. Hirshfeld surfaces along with the corresponding fingerprint plots, has been applied to further understand, visualize and separate contributions of different types of intermolecular contacts in MBE and MIE (Turner et al., 2017; Spackman et al., 2021; McKinnon et al., 2007 ; Spackman & Jayatilaka, 2009 ). This analysis, to some extent, also allows a quantitative comparison of the intermolecular contacts at varied temperature and pressure conditions. The different colours in the d_norm surfaces relate to the distances of all contacts and the sums of the van der Waals radii of relevant atoms (Fig. 4).

Figure 4
Hirshfeld surfaces mapped with d_norm (from −0.2000 to 1.2000) of MBE and MIE molecules at selected low-temperature and high-pressure conditions. MBE at (a) 140 K/0.1 MPa, (b) 100 K/0.1 MPa, (c) 295 K/1.83 GPa and (d) 295 K/3.87 GPa. MIE at (e) 140 K/0.1 MPa, (f) 100 K/0.1 MPa, (g) 295 K/1.88 GPa and (h) 295 K/3.62 GPa. The white, red and blue colours indicate contacts that are equal, shorter and longer, respectively, than the sums of the van der Waals radii of respective atoms.

As mentioned above, it can be seen that the shortest, relative to their van der Waals radii of interacting atoms, are the X⋯X and X⋯H interactions, while the longest interatomic distances have been found for the H⋯H contacts. The slightly different behaviour for MBE and MIE is shown in the Hirshfeld surface fingerprint plots. They present d_e as a function of d_i and also visualize the relative contributions of all types of contacts to the Hirshfeld surfaces (Figs. 5, S8 and S9). These two-dimensional diagrams show the general typical differences between the investigated structures: (i) the relatively shorter contacts for MBE than for MIE (the van der Waals radius for Br is smaller than for I) and (ii) more compressed, and more symmetrical, fingerprint plots for MBE and MIE determined at high pressures, as their contacts are compressed too. Inspection of the decomposed fingerprint plots facilitates a simple comparison between MBE and MIE molecules in their crystal structures determined at various temperature and pressure conditions. Also, the changes in contact distances and the shape of the X⋯H and H⋯H regions should be noticed. The shortest X⋯X contacts comprise only, on average, ∼2% of the total Hirshfeld surface area for both MBE and MIE and their contributions slightly increase with lowering temperature and increasing pressure. The clearly higher average contributions of ∼45%, that are the lowest at 100 K and ∼3.7 GPa, are noted for the X⋯H contacts (Saha et al., 2018). The longest H⋯H contacts dominate the Hirshfeld surfaces, for both MBE and MIE at all thermodynamic conditions, with a percentage average contribution of ∼53%. Also, the contributions of those contacts slightly increase upon decreasing temperature and increasing pressure.

Figure 5
Distribution of X⋯X, X⋯H and H⋯H contacts, based on their relative contributions to the Hirshfeld surface area, for MBE and MIE at various selected temperature and pressure conditions (X = Br for MBE, and X = I for MIE).

The observation of progressive shortening of all contact distances confirms their attractive nature, whereas the changes associated with contributions of particular groups of contacts to the Hirshfeld surface area suggest their hierarchical and competitive character.

4. Summary and conclusions

Bromoethane (MBE) and iodoethane (MIE) characterized by melting points of ∼160 K, with the lower melting point for MBE than for MIE, have been investigated at ambient-pressure low-temperature and ambient-temperature high-pressure conditions, starting with in situ crystallization of those liquids followed by single-crystal X-ray diffraction. The results of these studies, supported by the ambient-temperature compressibility and ambient-pressure thermoanalytical DSC measurements, demonstrate the clear similarities and only slight differences in the behaviour of these two isostructural crystals. Besides the close structural relationship both MBE and MIE show just one monoclinic phase that is stable down to 100 K/0.1 MPa and up to ∼ 295 K/3.7 GPa with no phase transition or symmetry change. These facts make them the perfect compounds for monitoring and analysing the influence of external low-temperature and high-pressure conditions on the simple molecular systems.

The study illustrates that the crystal structure of MBE is somewhat more close packed than its iodine analogue, MIE. This is related to the properties of different halogen atoms present in both crystal structures. Both decreasing temperature and increasing pressure, in the studied regimes, do not significantly affect the molecular dimensions, but clearly the intermolecular distances in both crystals are reduced. As a result the shorter and new intermolecular contacts are introduced, in particular, with compression of the crystals. The shortest type-I X⋯X (X = Br for MBE, and X = I for MIE) interactions, with average distances of ∼91% of the sums of the van der Waals radii of respective atoms have been found at the highest investigated pressures of ∼295 K/3.7 GPa. The distorted type-I X⋯H contacts, at the highest pressure of ∼295 K/3.7 GPa, are in a similar relation (93%) on average, of the sums of the van der Waals radii. The longest, mostly with the distances above the sum of the van der Waals radii, are the separation distances for H⋯H contacts.

The Hirshfeld surface analysis shows that the relative contributions of particular types of contacts are somewhat different for MBE and MIE, and slightly change upon decreasing temperature and increasing pressure confirming their attractive and hierarchical nature. The contribution of the strongest X⋯X contacts is as small as ∼2%, whereas the contribution of H⋯H contacts is as much as ∼53%. The input of those two types of contacts increase upon decreasing temperature and increasing pressure whereas the contributions of X⋯H contacts are gradually reduced to ∼45% at the highest pressure of ∼295 K/3.7 GPa. This indicates that both MBE and MIE molecules in their crystals, upon cooling or compression, are brought closer to each other and as a result the intermolecular distances get shorter without main changes in their mutual orientation. It is also worth mentioning that a detailed analysis of the crystal structures of relatively simple and analogous compounds together with monitoring their behaviour under temperature and pressure variations clearly contribute to the understanding of the noncovalent intermolecular interactions and their role on the fundamental processes of crystallization and solid-state structure formation. These along with the specific response of the crystals to the external forces could be used in the design of new materials through utilization of the crystal engineering approach.

Supporting information

CCDC references: 2213873; 2213874; 2213875; 2213876; 2213877; 2213878; 2213879; 2213880; 2213881; 2213882; 2213883; 2213884; 2213885; 2213886

Crystal structure: contains datablocks global, MBE_140K, MBE_120K, MBE_100K, MBE_1.83GPa, MBE_2.13GPa, MBE_3.07GPa, MBE_3.87GPa, MIE_140K, MIE_120K, MIE_100K, MIE_1.88GPa, MIE_2.40GPa, MIE_3.18GPa, MIE_3.62GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073sup1.cif

Structure factors: contains datablock MBE_140K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_140Ksup2.hkl

Structure factors: contains datablock MBE_120K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_120Ksup3.hkl

Structure factors: contains datablock MBE_100K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_100Ksup4.hkl

Structure factors: contains datablock MBE_1.83GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_1.83GPasup5.hkl

Structure factors: contains datablock MBE_2.13GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_2.13GPasup6.hkl

Structure factors: contains datablock MBE_3.07GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_3.07GPasup7.hkl

Structure factors: contains datablock MBE_3.87GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_3.87GPasup8.hkl

Structure factors: contains datablock MIE_140K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_140Ksup9.hkl

Structure factors: contains datablock MIE_120K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_120Ksup10.hkl

Structure factors: contains datablock MIE_100K. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_100Ksup11.hkl

Structure factors: contains datablock MIE_1.88GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_1.88GPasup12.hkl

Structure factors: contains datablock MIE_2.40GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_2.40GPasup13.hkl

Structure factors: contains datablock MIE_3.18GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_3.18GPasup14.hkl

Structure factors: contains datablock MIE_3.62GPa. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_3.62GPasup15.hkl

Tables S1-S14 and Figs S1-S9. DOI: https://doi.org/10.1107/S2052520622010149/aw5073sup16.pdf

Supporting information file. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MBE_1.83GPasup17.cml

Supporting information file. DOI: https://doi.org/10.1107/S2052520622010149/aw5073MIE_1.88GPasup18.cml

Computing details top

Data collection: CrysAlis PRO 1.171.38.46 (Rigaku Oxford Diffraction, 2015) for MBE_140K, MBE_120K, MBE_100K, MBE_1.83GPa, MBE_2.13GPa, MBE_3.07GPa, MBE_3.87GPa, MIE_1.88GPa, MIE_2.40GPa, MIE_3.18GPa, MIE_3.62GPa; CrysAlis PRO 1.171.40.84a (Rigaku Oxford Diffraction, 2020) for MIE_140K, MIE_120K, MIE_100K. For all structures, cell refinement: CrysAlis PRO 1.171.40.84a (Rigaku Oxford Diffraction, 2020); data reduction: CrysAlis PRO 1.171.40.84a (Rigaku Oxford Diffraction, 2020); program(s) used to solve structure: SHELXS2013/1 (Sheldrick, 2013); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2018); molecular graphics: Mercury (Macrae at al., 2020); software used to prepare material for publication: SHELXL2018/3 (Sheldrick, 2018).

bromoethane (MBE_140K) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 1.914 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5329 (5) Å	Cell parameters from 1993 reflections
b = 9.9018 (10) Å	θ = 3.8–29.2°
c = 7.0147 (7) Å	µ = 10.61 mm⁻¹
β = 100.309 (9)°	T = 140 K
V = 378.10 (6) Å³	Irregular, colourless
Z = 4	0.1 × 0.1 × 0.1 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	756 reflections with I > 2σ(I)
ω scans	R_int = 0.053
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.6°
T_min = 0.016, T_max = 1.000	h = −7→7
5889 measured reflections	k = −12→12
872 independent reflections	l = −9→9

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.021	H-atom parameters constrained
wR(F²) = 0.043	w = 1/[σ²(F_o²) + (0.013P)²] where P = (F_o² + 2F_c²)/3
S = 1.04	(Δ/σ)_max = 0.001
872 reflections	Δρ_max = 0.38 e Å⁻³
30 parameters	Δρ_min = −0.34 e Å⁻³
0 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0204 (12)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22329 (5)	0.94168 (3)	0.80655 (4)	0.03806 (13)
C1	−0.1001 (5)	0.8640 (3)	0.7095 (4)	0.0386 (6)
H11	−0.224931	0.932637	0.710497	0.046*
H12	−0.107459	0.834873	0.576517	0.046*
C2	−0.1528 (5)	0.7472 (2)	0.8284 (4)	0.0371 (6)
H21	−0.312024	0.711212	0.776243	0.056*
H22	−0.149796	0.776155	0.959431	0.056*
H23	−0.030541	0.678601	0.826538	0.056*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.02607 (17)	0.04072 (19)	0.04835 (19)	−0.00667 (11)	0.00927 (12)	−0.00326 (11)
C1	0.0239 (14)	0.0447 (16)	0.0446 (14)	−0.0019 (12)	−0.0010 (11)	0.0059 (12)
C2	0.0292 (13)	0.0278 (12)	0.0514 (15)	−0.0029 (11)	−0.0007 (11)	0.0006 (11)

Geometric parameters (Å, º) top

Br1—C1	1.955 (3)	C2—H21	0.9600
C1—C2	1.485 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.72 (17)	C1—C2—H21	109.5
C2—C1—H11	109.3	C1—C2—H22	109.5
Br1—C1—H11	109.3	H21—C2—H22	109.5
C2—C1—H12	109.3	C1—C2—H23	109.5
Br1—C1—H12	109.3	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

bromoethane (MBE_120K) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 1.934 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5204 (5) Å	Cell parameters from 2247 reflections
b = 9.8941 (8) Å	θ = 3.8–30.5°
c = 6.9655 (6) Å	µ = 10.72 mm⁻¹
β = 100.340 (9)°	T = 120 K
V = 374.27 (6) Å³	Irregular, colourless
Z = 4	0.1 × 0.1 × 0.1 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	759 reflections with I > 2σ(I)
ω scans	R_int = 0.049
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.6°
T_min = 0.060, T_max = 1.000	h = −7→7
5791 measured reflections	k = −12→12
861 independent reflections	l = −9→9

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.022	Hydrogen site location: difference Fourier map
wR(F²) = 0.051	H-atom parameters constrained
S = 1.09	w = 1/[σ²(F_o²) + (0.0189P)² + 0.0456P] where P = (F_o² + 2F_c²)/3
861 reflections	(Δ/σ)_max = 0.001
29 parameters	Δρ_max = 0.65 e Å⁻³
0 restraints	Δρ_min = −0.56 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22413 (5)	0.94175 (3)	0.80877 (4)	0.02979 (11)
C1	−0.0997 (5)	0.8631 (3)	0.7093 (4)	0.0302 (6)
H11	−0.225420	0.931603	0.708633	0.036*
H12	−0.105360	0.833210	0.575882	0.036*
C2	−0.1529 (5)	0.7464 (3)	0.8303 (4)	0.0292 (6)
H21	−0.310981	0.709123	0.776268	0.044*
H22	−0.153548	0.776386	0.961324	0.044*
H23	−0.028416	0.678491	0.831480	0.044*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.02011 (17)	0.03111 (18)	0.03880 (18)	−0.00533 (11)	0.00707 (12)	−0.00266 (11)
C1	0.0177 (13)	0.0331 (15)	0.0370 (14)	−0.0006 (12)	−0.0022 (11)	0.0044 (11)
C2	0.0214 (14)	0.0240 (13)	0.0404 (15)	−0.0022 (11)	0.0008 (11)	−0.0010 (11)

Geometric parameters (Å, º) top

Br1—C1	1.959 (3)	C2—H21	0.9600
C1—C2	1.490 (4)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.59 (18)	C1—C2—H21	109.5
C2—C1—H11	109.3	C1—C2—H22	109.5
Br1—C1—H11	109.3	H21—C2—H22	109.5
C2—C1—H12	109.3	C1—C2—H23	109.5
Br1—C1—H12	109.3	H21—C2—H23	109.5
H11—C1—H12	108.0	H22—C2—H23	109.5

bromoethane (MBE_100K) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 1.950 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5087 (4) Å	Cell parameters from 2450 reflections
b = 9.8814 (8) Å	θ = 3.6–30.6°
c = 6.9315 (6) Å	µ = 10.81 mm⁻¹
β = 100.379 (8)°	T = 100 K
V = 371.13 (5) Å³	Irregular, colourless
Z = 4	0.1 × 0.1 × 0.1 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	770 reflections with I > 2σ(I)
ω scans	R_int = 0.049
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.6°
T_min = 0.054, T_max = 1.000	h = −7→7
5716 measured reflections	k = −12→12
850 independent reflections	l = −8→8

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.021	Hydrogen site location: difference Fourier map
wR(F²) = 0.048	H-atom parameters constrained
S = 1.08	w = 1/[σ²(F_o²) + (0.0195P)²] where P = (F_o² + 2F_c²)/3
850 reflections	(Δ/σ)_max = 0.001
29 parameters	Δρ_max = 0.70 e Å⁻³
0 restraints	Δρ_min = −0.54 e Å⁻³

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22480 (4)	0.94184 (2)	0.81028 (4)	0.02419 (11)
C1	−0.1004 (5)	0.8627 (3)	0.7094 (4)	0.0241 (5)
H11	−0.226595	0.931305	0.708255	0.029*
H12	−0.105678	0.832564	0.575534	0.029*
C2	−0.1534 (5)	0.7460 (3)	0.8318 (4)	0.0246 (5)
H21	−0.311771	0.708441	0.777618	0.037*
H22	−0.154132	0.776292	0.963312	0.037*
H23	−0.028481	0.678048	0.833356	0.037*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.01560 (16)	0.02502 (16)	0.03239 (16)	−0.00434 (10)	0.00546 (11)	−0.00231 (9)
C1	0.0142 (12)	0.0260 (14)	0.0307 (13)	−0.0014 (11)	0.0001 (10)	0.0023 (10)
C2	0.0189 (12)	0.0189 (12)	0.0340 (13)	−0.0015 (11)	−0.0007 (10)	0.0003 (10)

Geometric parameters (Å, º) top

Br1—C1	1.964 (3)	C2—H21	0.9600
C1—C2	1.492 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.40 (17)	C1—C2—H21	109.5
C2—C1—H11	109.3	C1—C2—H22	109.5
Br1—C1—H11	109.3	H21—C2—H22	109.5
C2—C1—H12	109.3	C1—C2—H23	109.5
Br1—C1—H12	109.3	H21—C2—H23	109.5
H11—C1—H12	108.0	H22—C2—H23	109.5

bromoethane (MBE_1.83GPa) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 2.227 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.2831 (6) Å	Cell parameters from 890 reflections
b = 9.4910 (9) Å	θ = 4.5–26.7°
c = 6.5957 (6) Å	µ = 12.34 mm⁻¹
β = 100.623 (11)°	T = 295 K
V = 325.05 (6) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.06 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	258 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.018
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.8°, θ_min = 4.5°
T_min = 0.399, T_max = 1.000	h = −5→5
1621 measured reflections	k = −9→9
277 independent reflections	l = −7→7

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.016	Hydrogen site location: difference Fourier map
wR(F²) = 0.043	H-atom parameters constrained
S = 1.25	w = 1/[σ²(F_o²) + (0.0242P)² + 0.0253P] where P = (F_o² + 2F_c²)/3
277 reflections	(Δ/σ)_max < 0.001
29 parameters	Δρ_max = 0.15 e Å⁻³
0 restraints	Δρ_min = −0.15 e Å⁻³

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22748 (7)	0.94543 (4)	0.80994 (5)	0.0375 (2)
C1	−0.1072 (8)	0.8606 (4)	0.7009 (6)	0.0370 (10)
H11	−0.240616	0.931571	0.694375	0.044*
H12	−0.108388	0.826966	0.561889	0.044*
C2	−0.1645 (8)	0.7411 (4)	0.8319 (5)	0.0388 (11)
H21	−0.319524	0.694748	0.765993	0.058*
H22	−0.186742	0.776204	0.963999	0.058*
H23	−0.024189	0.675227	0.850151	0.058*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0299 (5)	0.0420 (5)	0.0409 (4)	−0.00559 (13)	0.0076 (4)	−0.00170 (13)
C1	0.029 (4)	0.042 (4)	0.039 (3)	0.0015 (16)	0.002 (3)	0.0027 (14)
C2	0.035 (4)	0.030 (4)	0.051 (3)	−0.0034 (15)	0.007 (3)	0.0007 (15)

Geometric parameters (Å, º) top

Br1—C1	1.955 (4)	C2—H21	0.9600
C1—C2	1.491 (5)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.5 (3)	C1—C2—H21	109.5
C2—C1—H11	109.3	C1—C2—H22	109.5
Br1—C1—H11	109.3	H21—C2—H22	109.5
C2—C1—H12	109.3	C1—C2—H23	109.5
Br1—C1—H12	109.3	H21—C2—H23	109.5
H11—C1—H12	108.0	H22—C2—H23	109.5

bromoethane (MBE_2.13GPa) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 2.271 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.2524 (6) Å	Cell parameters from 965 reflections
b = 9.4479 (12) Å	θ = 4.5–26.6°
c = 6.5350 (6) Å	µ = 12.58 mm⁻¹
β = 100.664 (10)°	T = 295 K
V = 318.69 (6) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.06 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	266 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.017
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.2°, θ_min = 4.5°
T_min = 0.360, T_max = 1.000	h = −6→5
1588 measured reflections	k = −9→9
277 independent reflections	l = −7→7

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.019	Hydrogen site location: difference Fourier map
wR(F²) = 0.052	H-atom parameters constrained
S = 1.15	w = 1/[σ²(F_o²) + (0.0381P)²] where P = (F_o² + 2F_c²)/3
277 reflections	(Δ/σ)_max < 0.001
29 parameters	Δρ_max = 0.29 e Å⁻³
0 restraints	Δρ_min = −0.27 e Å⁻³

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22831 (7)	0.94578 (4)	0.81119 (5)	0.0337 (2)
C1	−0.1085 (7)	0.8600 (4)	0.7008 (5)	0.0316 (8)
H11	−0.242908	0.931163	0.693862	0.038*
H12	−0.109328	0.826128	0.560575	0.038*
C2	−0.1656 (7)	0.7411 (4)	0.8317 (5)	0.0343 (9)
H21	−0.326991	0.698141	0.769212	0.051*
H22	−0.177623	0.775586	0.967755	0.051*
H23	−0.029406	0.672151	0.843243	0.051*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0280 (5)	0.0368 (7)	0.0366 (4)	−0.00532 (11)	0.0072 (4)	−0.00155 (11)
C1	0.022 (3)	0.038 (4)	0.033 (3)	−0.0018 (13)	0.001 (2)	0.0027 (13)
C2	0.023 (3)	0.039 (4)	0.039 (3)	−0.0001 (14)	−0.001 (2)	−0.0026 (15)

Geometric parameters (Å, º) top

Br1—C1	1.958 (4)	C2—H21	0.9600
C1—C2	1.476 (5)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.6 (2)	C1—C2—H21	109.5
C2—C1—H11	109.3	C1—C2—H22	109.5
Br1—C1—H11	109.3	H21—C2—H22	109.5
C2—C1—H12	109.3	C1—C2—H23	109.5
Br1—C1—H12	109.3	H21—C2—H23	109.5
H11—C1—H12	108.0	H22—C2—H23	109.5

bromoethane (MBE_3.07GPa) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 2.392 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.1730 (8) Å	Cell parameters from 793 reflections
b = 9.3305 (18) Å	θ = 4.5–26.0°
c = 6.3822 (9) Å	µ = 13.25 mm⁻¹
β = 100.777 (17)°	T = 295 K
V = 302.61 (9) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.05 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	244 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.024
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.8°, θ_min = 4.6°
T_min = 0.313, T_max = 1.000	h = −5→5
1501 measured reflections	k = −9→9
269 independent reflections	l = −7→7

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.031	Hydrogen site location: difference Fourier map
wR(F²) = 0.089	H-atom parameters constrained
S = 1.17	w = 1/[σ²(F_o²) + (0.0463P)² + 1.4387P] where P = (F_o² + 2F_c²)/3
269 reflections	(Δ/σ)_max < 0.001
29 parameters	Δρ_max = 0.40 e Å⁻³
0 restraints	Δρ_min = −0.43 e Å⁻³

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.22943 (17)	0.94651 (10)	0.81355 (13)	0.0311 (4)
C1	−0.1115 (17)	0.8605 (11)	0.6972 (13)	0.029 (2)
H11	−0.248273	0.932432	0.690057	0.035*
H12	−0.111371	0.826843	0.553409	0.035*
C2	−0.1705 (17)	0.7370 (10)	0.8328 (14)	0.029 (2)
H21	−0.343676	0.700997	0.777787	0.044*
H22	−0.161643	0.769142	0.976846	0.044*
H23	−0.043610	0.662278	0.830131	0.044*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0231 (9)	0.0387 (12)	0.0314 (8)	−0.0041 (3)	0.0049 (7)	−0.0011 (3)
C1	0.017 (7)	0.045 (10)	0.024 (6)	−0.003 (4)	−0.004 (6)	0.000 (4)
C2	0.012 (7)	0.040 (9)	0.032 (6)	0.001 (3)	−0.007 (6)	0.003 (4)

Geometric parameters (Å, º) top

Br1—C1	1.954 (9)	C2—H21	0.9600
C1—C2	1.506 (13)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	111.2 (6)	C1—C2—H21	109.5
C2—C1—H11	109.4	C1—C2—H22	109.5
Br1—C1—H11	109.4	H21—C2—H22	109.5
C2—C1—H12	109.4	C1—C2—H23	109.5
Br1—C1—H12	109.4	H21—C2—H23	109.5
H11—C1—H12	108.0	H22—C2—H23	109.5

bromoethane (MBE_3.87GPa) top

Crystal data top

C₂H₅Br	F(000) = 208
M_r = 108.96	D_x = 2.496 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.107 (3) Å	Cell parameters from 497 reflections
b = 9.206 (7) Å	θ = 4.6–25.4°
c = 6.285 (3) Å	µ = 13.83 mm⁻¹
β = 101.08 (6)°	T = 295 K
V = 290.0 (3) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.04 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	200 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.044
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.5°, θ_min = 4.6°
T_min = 0.752, T_max = 1.000	h = −5→5
1363 measured reflections	k = −8→8
252 independent reflections	l = −7→7

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.058	Hydrogen site location: difference Fourier map
wR(F²) = 0.135	H-atom parameters constrained
S = 1.23	w = 1/[σ²(F_o²) + (0.0305P)² + 6.6829P] where P = (F_o² + 2F_c²)/3
252 reflections	(Δ/σ)_max < 0.001
29 parameters	Δρ_max = 0.85 e Å⁻³
0 restraints	Δρ_min = −0.53 e Å⁻³

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Br1	0.2301 (4)	0.9465 (2)	0.8150 (3)	0.0439 (8)
C1	−0.110 (3)	0.866 (2)	0.690 (3)	0.041 (5)
H11	−0.246522	0.940412	0.678356	0.049*
H12	−0.106762	0.829836	0.545588	0.049*
C2	−0.177 (3)	0.739 (2)	0.836 (3)	0.037 (5)
H21	−0.366635	0.723815	0.808987	0.055*
H22	−0.115969	0.763481	0.985559	0.055*
H23	−0.090044	0.651925	0.802285	0.055*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.0370 (17)	0.055 (2)	0.0407 (14)	−0.0037 (9)	0.0111 (13)	−0.0004 (9)
C1	0.028 (15)	0.06 (2)	0.028 (12)	0.005 (8)	−0.004 (12)	−0.012 (8)
C2	0.033 (13)	0.021 (18)	0.057 (14)	−0.009 (7)	0.009 (12)	0.010 (8)

Geometric parameters (Å, º) top

Br1—C1	1.914 (18)	C2—H21	0.9600
C1—C2	1.56 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—Br1	109.5 (13)	C1—C2—H21	109.5
C2—C1—H11	109.8	C1—C2—H22	109.5
Br1—C1—H11	109.8	H21—C2—H22	109.5
C2—C1—H12	109.8	C1—C2—H23	109.5
Br1—C1—H12	109.8	H21—C2—H23	109.5
H11—C1—H12	108.2	H22—C2—H23	109.5

iodoethane (MIE_140K) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 2.456 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.85463 (16) Å	Cell parameters from 5769 reflections
b = 10.1532 (3) Å	θ = 3.5–36.5°
c = 7.2722 (2) Å	µ = 7.36 mm⁻¹
β = 102.701 (3)°	T = 140 K
V = 421.71 (2) Å³	Irregular, colourless
Z = 4	0.2 × 0.2 × 0.2 mm

Data collection top

Xcalibur, Eos diffractometer	952 reflections with I > 2σ(I)
ω scans	R_int = 0.017
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.5°
T_min = 0.067, T_max = 1.000	h = −7→7
7391 measured reflections	k = −13→13
969 independent reflections	l = −9→9

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.012	H-atom parameters constrained
wR(F²) = 0.027	w = 1/[σ²(F_o²) + (0.0107P)² + 0.1879P] where P = (F_o² + 2F_c²)/3
S = 1.25	(Δ/σ)_max = 0.002
969 reflections	Δρ_max = 0.35 e Å⁻³
30 parameters	Δρ_min = −0.28 e Å⁻³
0 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0605 (10)

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22073 (2)	0.94440 (2)	0.80381 (2)	0.03008 (7)
C1	−0.1201 (3)	0.8565 (2)	0.7078 (3)	0.0342 (4)
H11	−0.239373	0.922950	0.706564	0.041*
H12	−0.134949	0.825184	0.579651	0.041*
C2	−0.1607 (3)	0.74417 (19)	0.8298 (3)	0.0307 (4)
H21	−0.314213	0.708501	0.782429	0.046*
H22	−0.148412	0.774897	0.956419	0.046*
H23	−0.045493	0.677039	0.828792	0.046*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.02362 (9)	0.03282 (10)	0.03491 (9)	−0.00469 (4)	0.00885 (5)	−0.00215 (5)
C1	0.0245 (9)	0.0374 (11)	0.0366 (10)	−0.0052 (8)	−0.0025 (7)	0.0050 (8)
C2	0.0261 (9)	0.0249 (9)	0.0400 (10)	−0.0025 (7)	0.0045 (7)	−0.0003 (8)

Geometric parameters (Å, º) top

I1—C1	2.1572 (19)	C2—H21	0.9600
C1—C2	1.495 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.33 (12)	C1—C2—H21	109.5
C2—C1—H11	109.1	C1—C2—H22	109.5
I1—C1—H11	109.1	H21—C2—H22	109.5
C2—C1—H12	109.1	C1—C2—H23	109.5
I1—C1—H12	109.1	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

iodoethane (MIE_120K) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 2.477 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.83962 (16) Å	Cell parameters from 6013 reflections
b = 10.1442 (3) Å	θ = 3.6–36.4°
c = 7.2368 (2) Å	µ = 7.42 mm⁻¹
β = 102.705 (3)°	T = 120 K
V = 418.20 (2) Å³	Irregular, colourless
Z = 4	0.2 × 0.2 × 0.2 mm

Data collection top

Xcalibur, Eos diffractometer	949 reflections with I > 2σ(I)
ω scans	R_int = 0.018
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.5°
T_min = 0.068, T_max = 1.000	h = −7→7
7329 measured reflections	k = −13→13
962 independent reflections	l = −9→9

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.012	H-atom parameters constrained
wR(F²) = 0.025	w = 1/[σ²(F_o²) + (0.009P)² + 0.2205P] where P = (F_o² + 2F_c²)/3
S = 1.27	(Δ/σ)_max < 0.001
962 reflections	Δρ_max = 0.30 e Å⁻³
30 parameters	Δρ_min = −0.27 e Å⁻³
0 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0514 (9)

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22105 (2)	0.94448 (2)	0.80480 (2)	0.02475 (7)
C1	−0.1208 (3)	0.8562 (2)	0.7071 (3)	0.0281 (4)
H11	−0.240753	0.922628	0.705450	0.034*
H12	−0.135135	0.824693	0.578547	0.034*
C2	−0.1613 (3)	0.74362 (18)	0.8305 (3)	0.0257 (4)
H21	−0.315549	0.708120	0.783567	0.039*
H22	−0.148029	0.774440	0.957850	0.039*
H23	−0.046292	0.676237	0.829059	0.039*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.01932 (8)	0.02677 (9)	0.02915 (9)	−0.00391 (4)	0.00751 (5)	−0.00183 (5)
C1	0.0194 (8)	0.0301 (10)	0.0311 (9)	−0.0047 (7)	−0.0025 (7)	0.0040 (8)
C2	0.0218 (9)	0.0207 (9)	0.0334 (10)	−0.0022 (7)	0.0033 (7)	−0.0005 (7)

Geometric parameters (Å, º) top

I1—C1	2.1603 (18)	C2—H21	0.9600
C1—C2	1.500 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.10 (12)	C1—C2—H21	109.5
C2—C1—H11	109.2	C1—C2—H22	109.5
I1—C1—H11	109.2	H21—C2—H22	109.5
C2—C1—H12	109.2	C1—C2—H23	109.5
I1—C1—H12	109.2	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

iodoethane (MIE_100K) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 2.496 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.82719 (15) Å	Cell parameters from 6155 reflections
b = 10.1348 (2) Å	θ = 3.5–36.6°
c = 7.20284 (19) Å	µ = 7.48 mm⁻¹
β = 102.711 (3)°	T = 100 K
V = 414.96 (2) Å³	Irregular, colourless
Z = 4	0.2 × 0.2 × 0.2 mm

Data collection top

Xcalibur, Eos diffractometer	951 reflections with I > 2σ(I)
ω scans	R_int = 0.016
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 27.5°, θ_min = 3.5°
T_min = 0.105, T_max = 1.000	h = −7→7
7277 measured reflections	k = −13→13
959 independent reflections	l = −9→9

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.011	H-atom parameters constrained
wR(F²) = 0.023	w = 1/[σ²(F_o²) + (0.0067P)² + 0.256P] where P = (F_o² + 2F_c²)/3
S = 1.31	(Δ/σ)_max = 0.001
959 reflections	Δρ_max = 0.35 e Å⁻³
30 parameters	Δρ_min = −0.24 e Å⁻³
0 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0398 (6)

Special details top

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22129 (2)	0.94457 (2)	0.80560 (2)	0.02005 (6)
C1	−0.1211 (3)	0.85589 (19)	0.7069 (3)	0.0232 (4)
H11	−0.241552	0.922316	0.704706	0.028*
H12	−0.134945	0.824167	0.577842	0.028*
C2	−0.1618 (3)	0.74322 (18)	0.8313 (3)	0.0210 (4)
H21	−0.316456	0.707785	0.784332	0.032*
H22	−0.148153	0.774193	0.959194	0.032*
H23	−0.046697	0.675675	0.829797	0.032*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.01578 (7)	0.02131 (8)	0.02392 (8)	−0.00325 (4)	0.00623 (5)	−0.00155 (4)
C1	0.0162 (8)	0.0251 (10)	0.0255 (9)	−0.0039 (7)	−0.0018 (7)	0.0031 (7)
C2	0.0180 (8)	0.0165 (8)	0.0278 (9)	−0.0018 (7)	0.0031 (7)	−0.0007 (7)

Geometric parameters (Å, º) top

I1—C1	2.1612 (18)	C2—H21	0.9600
C1—C2	1.502 (3)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.04 (11)	C1—C2—H21	109.5
C2—C1—H11	109.2	C1—C2—H22	109.5
I1—C1—H11	109.2	H21—C2—H22	109.5
C2—C1—H12	109.2	C1—C2—H23	109.5
I1—C1—H12	109.2	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

iodoethane (MIE_1.88GPa) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 2.862 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5767 (13) Å	Cell parameters from 1135 reflections
b = 9.7073 (6) Å	θ = 4.8–26.7°
c = 6.8424 (3) Å	µ = 8.57 mm⁻¹
β = 102.262 (10)°	T = 295 K
V = 361.96 (9) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.21 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	293 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.025
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.8°, θ_min = 4.8°
T_min = 0.118, T_max = 1.000	h = −4→4
1671 measured reflections	k = −11→11
299 independent reflections	l = −8→8

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.026	H-atom parameters constrained
wR(F²) = 0.069	w = 1/[σ²(F_o²) + (0.0437P)² + 0.2787P] where P = (F_o² + 2F_c²)/3
S = 1.26	(Δ/σ)_max < 0.001
299 reflections	Δρ_max = 0.47 e Å⁻³
30 parameters	Δρ_min = −0.41 e Å⁻³
6 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.172 (12)

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22464 (12)	0.94797 (3)	0.80455 (5)	0.0311 (6)
C1	−0.128 (2)	0.8521 (6)	0.6992 (9)	0.031 (4)
H11	−0.255298	0.921028	0.691250	0.038*
H12	−0.135882	0.816336	0.565615	0.038*
C2	−0.174 (2)	0.7385 (5)	0.8310 (9)	0.031 (2)
H21	−0.333166	0.699860	0.779321	0.046*
H22	−0.167089	0.773435	0.963316	0.046*
H23	−0.051160	0.668425	0.835826	0.046*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.0249 (17)	0.0338 (6)	0.0351 (5)	−0.00405 (14)	0.0077 (5)	−0.00091 (11)
C1	0.014 (16)	0.041 (5)	0.035 (3)	−0.001 (3)	−0.002 (5)	−0.001 (2)
C2	0.019 (9)	0.034 (3)	0.036 (3)	0.001 (3)	−0.001 (4)	−0.002 (2)

Geometric parameters (Å, º) top

I1—C1	2.155 (12)	C2—H21	0.9600
C1—C2	1.482 (9)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.5 (6)	C1—C2—H21	109.5
C2—C1—H11	109.1	C1—C2—H22	109.5
I1—C1—H11	109.1	H21—C2—H22	109.5
C2—C1—H12	109.1	C1—C2—H23	109.5
I1—C1—H12	109.1	H21—C2—H23	109.5
H11—C1—H12	107.8	H22—C2—H23	109.5

iodoethane (MIE_2.40GPa) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 2.944 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.5292 (9) Å	Cell parameters from 1175 reflections
b = 9.6336 (7) Å	θ = 4.3–26.9°
c = 6.7597 (2) Å	µ = 8.82 mm⁻¹
β = 102.209 (8)°	T = 295 K
V = 351.92 (6) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.19 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	294 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.035
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.9°, θ_min = 4.3°
T_min = 0.715, T_max = 1.000	h = −4→4
1557 measured reflections	k = −10→10
301 independent reflections	l = −8→8

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.038	Hydrogen site location: difference Fourier map
wR(F²) = 0.138	H-atom parameters constrained
S = 1.38	w = 1/[σ²(F_o²) + (0.0821P)² + 1.0813P] where P = (F_o² + 2F_c²)/3
301 reflections	(Δ/σ)_max < 0.001
29 parameters	Δρ_max = 0.74 e Å⁻³
6 restraints	Δρ_min = −0.68 e Å⁻³

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22537 (19)	0.94856 (7)	0.80548 (10)	0.0296 (7)
C1	−0.124 (3)	0.8516 (10)	0.6990 (16)	0.031 (3)
H11	−0.253094	0.920963	0.688887	0.038*
H12	−0.129750	0.815306	0.564214	0.038*
C2	−0.175 (3)	0.7362 (10)	0.8318 (16)	0.032 (4)
H21	−0.333236	0.695565	0.774407	0.048*
H22	−0.177696	0.772030	0.963940	0.048*
H23	−0.048655	0.666887	0.842426	0.048*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.021 (2)	0.0359 (11)	0.0323 (7)	−0.0039 (2)	0.0073 (7)	−0.0010 (2)
C1	0.030 (9)	0.028 (5)	0.037 (5)	−0.003 (4)	0.008 (5)	−0.005 (4)
C2	0.044 (16)	0.018 (7)	0.034 (5)	−0.008 (4)	0.007 (6)	−0.001 (4)

Geometric parameters (Å, º) top

I1—C1	2.129 (15)	C2—H21	0.9600
C1—C2	1.494 (14)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	113.5 (9)	C1—C2—H21	109.5
C2—C1—H11	108.9	C1—C2—H22	109.5
I1—C1—H11	108.9	H21—C2—H22	109.5
C2—C1—H12	108.9	C1—C2—H23	109.5
I1—C1—H12	108.9	H21—C2—H23	109.5
H11—C1—H12	107.7	H22—C2—H23	109.5

iodoethane (MIE_3.18GPa) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 3.056 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.4696 (8) Å	Cell parameters from 1055 reflections
b = 9.5403 (6) Å	θ = 4.3–26.7°
c = 6.6492 (6) Å	µ = 9.15 mm⁻¹
β = 102.280 (13)°	T = 295 K
V = 339.03 (6) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.16 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	271 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.042
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.9°, θ_min = 4.4°
T_min = 0.566, T_max = 1.000	h = −5→5
1416 measured reflections	k = −10→10
275 independent reflections	l = −7→7

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.035	H-atom parameters constrained
wR(F²) = 0.097	w = 1/[σ²(F_o²) + (0.046P)² + 2.2075P] where P = (F_o² + 2F_c²)/3
S = 1.32	(Δ/σ)_max < 0.001
275 reflections	Δρ_max = 0.60 e Å⁻³
30 parameters	Δρ_min = −0.54 e Å⁻³
12 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.041 (12)

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22637 (18)	0.94925 (7)	0.80655 (13)	0.0271 (7)
C1	−0.132 (3)	0.8520 (12)	0.6952 (19)	0.026 (3)
H11	−0.262191	0.922002	0.685983	0.031*
H12	−0.138471	0.815473	0.557964	0.031*
C2	−0.180 (3)	0.7345 (11)	0.833 (2)	0.032 (4)
H21	−0.348108	0.701455	0.788409	0.048*
H22	−0.155966	0.768021	0.972405	0.048*
H23	−0.065003	0.659049	0.827712	0.048*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.0253 (16)	0.0299 (9)	0.0264 (10)	−0.0031 (2)	0.0061 (11)	−0.0006 (2)
C1	0.025 (9)	0.027 (5)	0.024 (7)	−0.002 (4)	0.003 (7)	−0.001 (4)
C2	0.055 (14)	0.016 (6)	0.029 (8)	−0.005 (5)	0.016 (9)	−0.008 (4)

Geometric parameters (Å, º) top

I1—C1	2.151 (15)	C2—H21	0.9600
C1—C2	1.508 (15)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.0 (10)	C1—C2—H21	109.5
C2—C1—H11	109.2	C1—C2—H22	109.5
I1—C1—H11	109.2	H21—C2—H22	109.5
C2—C1—H12	109.2	C1—C2—H23	109.5
I1—C1—H12	109.2	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

iodoethane (MIE_3.62GPa) top

Crystal data top

C₂H₅I	F(000) = 280
M_r = 155.96	D_x = 3.123 Mg m⁻³
Monoclinic, P2₁/n	Mo Kα radiation, λ = 0.71073 Å
a = 5.4335 (11) Å	Cell parameters from 973 reflections
b = 9.4863 (7) Å	θ = 4.9–26.5°
c = 6.5840 (4) Å	µ = 9.35 mm⁻¹
β = 102.191 (12)°	T = 295 K
V = 331.71 (8) Å³	Disc, colourless
Z = 4	0.37 × 0.37 × 0.14 mm

Data collection top

KUMA KM4-CCD, Eos diffractometer	263 reflections with I > 2σ(I)
φ– and ω–scans	R_int = 0.022
Absorption correction: multi-scan CrysAlisPro 1.171.40.84a (Rigaku Oxford Diffraction, 2020) Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.	θ_max = 26.6°, θ_min = 4.9°
T_min = 0.073, T_max = 1.000	h = −4→4
1394 measured reflections	k = −10→10
270 independent reflections	l = −8→8

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F² > 2σ(F²)] = 0.026	H-atom parameters constrained
wR(F²) = 0.070	w = 1/[σ²(F_o²) + (0.0354P)² + 1.1239P] where P = (F_o² + 2F_c²)/3
S = 1.36	(Δ/σ)_max < 0.001
270 reflections	Δρ_max = 0.41 e Å⁻³
30 parameters	Δρ_min = −0.37 e Å⁻³
6 restraints	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.055 (9)

Special details top

Refinement. The diamond-anvil cell (DAC) imposes severe restrictions on which reflections can be collected, resulting in a low data:parameter ratio.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
I1	0.22645 (14)	0.94979 (5)	0.80717 (8)	0.0215 (5)
C1	−0.131 (3)	0.8504 (9)	0.6952 (13)	0.024 (3)
H11	−0.263232	0.920209	0.684699	0.029*
H12	−0.136098	0.813069	0.557196	0.029*
C2	−0.178 (3)	0.7332 (8)	0.8347 (13)	0.026 (4)
H21	−0.340856	0.692631	0.780432	0.039*
H22	−0.173882	0.769711	0.971451	0.039*
H23	−0.051040	0.662171	0.841642	0.039*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I1	0.0168 (14)	0.0235 (6)	0.0247 (5)	−0.00312 (18)	0.0059 (6)	−0.00050 (17)
C1	0.017 (9)	0.026 (4)	0.029 (5)	−0.005 (4)	0.004 (5)	0.003 (3)
C2	0.039 (15)	0.012 (6)	0.027 (4)	−0.002 (3)	0.008 (7)	0.001 (3)

Geometric parameters (Å, º) top

I1—C1	2.144 (13)	C2—H21	0.9600
C1—C2	1.499 (10)	C2—H22	0.9600
C1—H11	0.9700	C2—H23	0.9600
C1—H12	0.9700

C2—C1—I1	112.1 (7)	C1—C2—H21	109.5
C2—C1—H11	109.2	C1—C2—H22	109.5
I1—C1—H11	109.2	H21—C2—H22	109.5
C2—C1—H12	109.2	C1—C2—H23	109.5
I1—C1—H12	109.2	H21—C2—H23	109.5
H11—C1—H12	107.9	H22—C2—H23	109.5

Funding information

The following funding is acknowledged: National Science Centre, Poland (grant No. 2020/37/B/ST4/00982).

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Volume 78| Part 6| December 2022| Pages 868-875

https://doi.org/10.1107/S2052520622010149

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research papers\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Evolution of intermolecular contacts with temperature and pressure in bromo­ethane and iodo­ethane – a comparative study

1. Introduction

2. Experimental

2.1. In situ low-temperature crystallization

2.2. In situ high-pressure crystallization

2.3. Data collection, data reduction, structure solution and refinement

2.4. Differential scanning calorimetry measurements

2.5. Compressibility measurements

3. Results and discussion

4. Summary and conclusions

Supporting information

Funding information

References

research papers

Evolution of intermolecular contacts with temperature and pressure in bromoethane and iodoethane – a comparative study