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The title complex, C8H5I·C4H9NO, has an intermolecular charge-transfer bond N...I of 2.712 (2) Å, shorter than supposed earlier and the shortest known so far. Morpholine mol­ecules related by a b translation are linked to form a chain by N—H...O hydrogen bonds [N...O 3.110 (3) Å].

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199014705/na1436sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199014705/na1436Isup2.hkl
Contains datablock I

CCDC reference: 142782

Comment top

Morpholine and β-iodophenylacetylene react exothermically to form a stable 1:1 complex, first prepared by Southwick & Kirchner (1962), who suggested the charge-transfer structure, (I), on the strength of spectroscopic evidence. A single-crystal X-ray diffraction study (Baughman,1964) confirmed structure (I), with a rather short intermolecular N···I contact of ca 2.9 Å. However, the accuracy of the structure, determined by Fourier projections, was not high (R = 0.18).

The present study generally confirmed the earlier one, but is of much higher accuracy and at low temperature. Morpholine molecules related by a b translation, are linked into a chain by N4—H4···O1 hydrogen bonds [N···O 3.110 (3), N—H 0.93, H···O 2.19 Å, N—H—O 173°]. The heterocycle adopts a chair conformation, with the total puckering amplitude (Cremer & Pople, 1975) QT = 0.550 (3) Å. The C18—I bond points directly at the lone electron pair of the N4 atom. The C11—C17C18—I···N4 chain is practically linear: the maximum displacement from the best weighted least-squares line through it involves N4 that is 0.207 (4) Å from the line. The angle between this chain and the phenyl plane is 1.9 (2)°. The mean planes of the phenyl and morpholine groups form a dihedral angle of 49.9 (5)°. The I···N4 distance [2.712 (2) Å] proved much shorter than that reported by Baughman (2.9 Å), and is by far the closest intermolecular I···N contact known (with an iodine atom covalently bonded to carbon rather than halogen). The shortest such I···N contacts reported before, 2.93–2.95 Å, involved cyano-group nitrogen (Borgen et al., 1962; Imakubo et al., 1995), and the shortest one involving sp3 nitrogen was 2.99 (3) Å in the urotropine-iodoform complex (Dahl & Hassel, 1970).

The sum of van der Waals radii of I and N, is variously estimated as 3.53 Å (Bondi, 1964), 3.64 Å (Zefirov & Zorkii, 1989) and 3.67 Å (Rowland & Taylor, 1996) in an isotropic model. The 'shape' of the iodine atom is in fact anisotropic, with the smallest size along the continuation of the C—I bond, where a I···N van der Waals contact of 3.36 Å can be expected (Nyburg & Faerman, 1985). By any reckoning, the distance in (I) reveals a strong charge-transfer interaction, probably enhanced by high electronegativity of the ethyne group, estimated as 3.1 in Pauling's scale (Batsanov, 1990), i.e. exceeding that of Cl (3.0).

Experimental top

The complex was prepared by the method of Southwick and Kirchner (1962).

Structure description top

Morpholine and β-iodophenylacetylene react exothermically to form a stable 1:1 complex, first prepared by Southwick & Kirchner (1962), who suggested the charge-transfer structure, (I), on the strength of spectroscopic evidence. A single-crystal X-ray diffraction study (Baughman,1964) confirmed structure (I), with a rather short intermolecular N···I contact of ca 2.9 Å. However, the accuracy of the structure, determined by Fourier projections, was not high (R = 0.18).

The present study generally confirmed the earlier one, but is of much higher accuracy and at low temperature. Morpholine molecules related by a b translation, are linked into a chain by N4—H4···O1 hydrogen bonds [N···O 3.110 (3), N—H 0.93, H···O 2.19 Å, N—H—O 173°]. The heterocycle adopts a chair conformation, with the total puckering amplitude (Cremer & Pople, 1975) QT = 0.550 (3) Å. The C18—I bond points directly at the lone electron pair of the N4 atom. The C11—C17C18—I···N4 chain is practically linear: the maximum displacement from the best weighted least-squares line through it involves N4 that is 0.207 (4) Å from the line. The angle between this chain and the phenyl plane is 1.9 (2)°. The mean planes of the phenyl and morpholine groups form a dihedral angle of 49.9 (5)°. The I···N4 distance [2.712 (2) Å] proved much shorter than that reported by Baughman (2.9 Å), and is by far the closest intermolecular I···N contact known (with an iodine atom covalently bonded to carbon rather than halogen). The shortest such I···N contacts reported before, 2.93–2.95 Å, involved cyano-group nitrogen (Borgen et al., 1962; Imakubo et al., 1995), and the shortest one involving sp3 nitrogen was 2.99 (3) Å in the urotropine-iodoform complex (Dahl & Hassel, 1970).

The sum of van der Waals radii of I and N, is variously estimated as 3.53 Å (Bondi, 1964), 3.64 Å (Zefirov & Zorkii, 1989) and 3.67 Å (Rowland & Taylor, 1996) in an isotropic model. The 'shape' of the iodine atom is in fact anisotropic, with the smallest size along the continuation of the C—I bond, where a I···N van der Waals contact of 3.36 Å can be expected (Nyburg & Faerman, 1985). By any reckoning, the distance in (I) reveals a strong charge-transfer interaction, probably enhanced by high electronegativity of the ethyne group, estimated as 3.1 in Pauling's scale (Batsanov, 1990), i.e. exceeding that of Cl (3.0).

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: SHELXTL (Sheldrick, 1995); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. Molecular structure showing 50% probability displacement ellipsoids, and the hydrogen bonds and charge-transfer interactions.
morpholine β-iodophenylacetylene complex (1:1) top
Crystal data top
C8H5I·C4H9NODx = 1.663 Mg m3
Mr = 315.14Melting point: 343-353 K K
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 8.867 (1) ÅCell parameters from 470 reflections
b = 4.8579 (2) Åθ = 12–23°
c = 29.390 (2) ŵ = 2.52 mm1
β = 96.05 (1)°T = 150 K
V = 1258.9 (2) Å3Plate, colourless
Z = 40.32 × 0.30 × 0.12 mm
F(000) = 616
Data collection top
Siemens SMART 1K CCD area detector
diffractometer
3316 independent reflections
Radiation source: fine-focus sealed tube3136 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.027
Detector resolution: 8 pixels mm-1θmax = 29.0°, θmin = 1.4°
ω scansh = 1212
Absorption correction: integration
(XPREP in SHELXTL; Sheldrick, 1995), before correction Rint = 0.080
k = 66
Tmin = 0.520, Tmax = 0.752l = 3930
10880 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.029Hydrogen site location: difference Fourier map
wR(F2) = 0.058H-atom parameters constrained
S = 1.30Calculated w = 1/[σ2(Fo2) + (0.0062P)2 + 1.8187P]
where P = (Fo2 + 2Fc2)/3
3316 reflections(Δ/σ)max = 0.001
136 parametersΔρmax = 0.60 e Å3
0 restraintsΔρmin = 0.83 e Å3
Crystal data top
C8H5I·C4H9NOV = 1258.9 (2) Å3
Mr = 315.14Z = 4
Monoclinic, P21/cMo Kα radiation
a = 8.867 (1) ŵ = 2.52 mm1
b = 4.8579 (2) ÅT = 150 K
c = 29.390 (2) Å0.32 × 0.30 × 0.12 mm
β = 96.05 (1)°
Data collection top
Siemens SMART 1K CCD area detector
diffractometer
3316 independent reflections
Absorption correction: integration
(XPREP in SHELXTL; Sheldrick, 1995), before correction Rint = 0.080
3136 reflections with I > 2σ(I)
Tmin = 0.520, Tmax = 0.752Rint = 0.027
10880 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0290 restraints
wR(F2) = 0.058H-atom parameters constrained
S = 1.30Δρmax = 0.60 e Å3
3316 reflectionsΔρmin = 0.83 e Å3
136 parameters
Special details top

Experimental. The data collection nominally covered over a hemisphere of reciprocal space, by a combination of four sets of exposures; each set had a different φ and/or 2θ angle for the crystal and each exposure covered 0.3° in ω. The crystal-to-detector distance was 4.54 cm. Crystal decay was monitored by repeating 50 initial frames at the end of data collection and analyzing 274 duplicate reflections.

Refinement. Refinement on F2 for ALL reflections except for 14 with very negative F2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The observed criterion of F2 > σ(F2) is used only for calculating refine_ls_R_factor_gt etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
I0.241246 (19)0.58943 (4)0.468957 (6)0.02788 (6)
O10.2882 (2)1.2521 (4)0.61565 (7)0.0349 (4)
C20.4176 (3)1.0834 (8)0.61074 (10)0.0383 (6)
H210.42710.94130.63500.050*
H220.51051.19800.61420.050*
C30.4027 (3)0.9453 (7)0.56413 (10)0.0321 (6)
H310.40341.08780.54010.042*
H320.49120.82350.56190.042*
N40.2625 (3)0.7821 (5)0.55599 (8)0.0303 (5)
H40.26860.63340.57600.039*
C50.1310 (3)0.9520 (7)0.56448 (10)0.0330 (6)
H510.03940.83440.56280.043*
H520.11451.09390.54030.043*
C60.1524 (3)1.0917 (7)0.61086 (10)0.0357 (6)
H610.06431.21220.61440.046*
H620.15740.95060.63530.046*
C110.2439 (3)0.2693 (8)0.31857 (10)0.0374 (7)
C120.3382 (6)0.3976 (11)0.29077 (15)0.0755 (15)
H120.40170.54400.30260.091*
C130.3414 (7)0.3153 (11)0.24561 (15)0.0820 (16)
H130.40890.40330.22720.098*
C140.2492 (5)0.1101 (11)0.22743 (12)0.0651 (13)
H140.24770.06270.19600.078*
C150.1587 (6)0.0271 (12)0.25492 (15)0.0756 (15)
H150.09770.17640.24290.091*
C160.1559 (5)0.0513 (11)0.30045 (13)0.0632 (12)
H160.09310.04540.31930.076*
C170.2375 (3)0.3592 (7)0.36494 (10)0.0346 (6)
C180.2338 (3)0.4460 (7)0.40305 (10)0.0333 (6)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
I0.02880 (9)0.03156 (9)0.02374 (9)0.00131 (8)0.00498 (6)0.00052 (8)
O10.0427 (11)0.0279 (10)0.0352 (11)0.0019 (9)0.0091 (9)0.0044 (9)
C20.0321 (14)0.0518 (18)0.0299 (14)0.0028 (14)0.0007 (11)0.0034 (14)
C30.0236 (12)0.0423 (16)0.0305 (13)0.0053 (11)0.0036 (10)0.0024 (12)
N40.0387 (12)0.0251 (11)0.0275 (11)0.0002 (10)0.0054 (9)0.0009 (9)
C50.0258 (12)0.0406 (16)0.0331 (14)0.0043 (12)0.0053 (10)0.0041 (12)
C60.0340 (14)0.0409 (16)0.0343 (14)0.0008 (13)0.0131 (11)0.0021 (13)
C110.0349 (14)0.0524 (19)0.0247 (13)0.0135 (14)0.0027 (10)0.0014 (13)
C120.114 (4)0.075 (3)0.044 (2)0.022 (3)0.039 (2)0.015 (2)
C130.133 (5)0.080 (3)0.041 (2)0.002 (3)0.046 (3)0.000 (2)
C140.085 (3)0.087 (3)0.0236 (15)0.036 (3)0.0068 (17)0.0041 (19)
C150.074 (3)0.113 (4)0.040 (2)0.009 (3)0.0064 (19)0.030 (2)
C160.060 (2)0.097 (3)0.0347 (18)0.013 (2)0.0126 (16)0.020 (2)
C170.0313 (13)0.0438 (17)0.0289 (14)0.0087 (12)0.0039 (10)0.0031 (12)
C180.0307 (13)0.0430 (16)0.0265 (13)0.0037 (12)0.0040 (10)0.0015 (12)
Geometric parameters (Å, º) top
I—C182.053 (3)C6—H610.9900
I—N42.712 (2)C6—H620.9900
O1—C61.429 (4)C11—C121.378 (5)
O1—C21.430 (4)C11—C161.388 (6)
C2—C31.518 (4)C11—C171.438 (4)
C2—H210.9900C12—C131.390 (6)
C2—H220.9900C12—H120.9500
C3—N41.473 (4)C13—C141.362 (7)
C3—H310.9900C13—H130.9500
C3—H320.9900C14—C151.370 (7)
N4—C51.471 (4)C14—H140.9500
N4—H40.9300C15—C161.394 (5)
C5—C61.517 (4)C15—H150.9500
C5—H510.9900C16—H160.9500
C5—H520.9900C17—C181.201 (4)
C18—I—N4177.84 (10)O1—C6—C5110.9 (2)
C6—O1—C2110.8 (2)O1—C6—H61109.5
O1—C2—C3110.5 (2)C5—C6—H61109.5
O1—C2—H21109.6O1—C6—H62109.5
C3—C2—H21109.6C5—C6—H62109.5
O1—C2—H22109.6H61—C6—H62108.0
C3—C2—H22109.6C12—C11—C16118.0 (3)
H21—C2—H22108.1C12—C11—C17120.8 (4)
N4—C3—C2112.1 (2)C16—C11—C17121.3 (3)
N4—C3—H31109.2C11—C12—C13120.7 (5)
C2—C3—H31109.2C11—C12—H12119.6
N4—C3—H32109.2C13—C12—H12119.6
C2—C3—H32109.2C14—C13—C12120.9 (4)
H31—C3—H32107.9C14—C13—H13119.6
C5—N4—C3110.0 (2)C12—C13—H13119.6
C5—N4—I112.09 (17)C13—C14—C15119.3 (4)
C3—N4—I108.20 (16)C13—C14—H14120.3
C5—N4—H4108.8C15—C14—H14120.3
C3—N4—H4108.8C14—C15—C16120.2 (5)
I—N4—H4108.8C14—C15—H15119.9
N4—C5—C6112.2 (2)C16—C15—H15119.9
N4—C5—H51109.2C11—C16—C15120.7 (4)
C6—C5—H51109.2C11—C16—H16119.6
N4—C5—H52109.2C15—C16—H16119.6
C6—C5—H52109.2C18—C17—C11177.0 (4)
H51—C5—H52107.9C17—C18—I176.5 (3)
O1—C2—C3—N456.5 (3)C3—N4—C5—C651.7 (3)
C2—C3—N4—C552.2 (3)N4—C5—C6—O155.7 (3)

Experimental details

Crystal data
Chemical formulaC8H5I·C4H9NO
Mr315.14
Crystal system, space groupMonoclinic, P21/c
Temperature (K)150
a, b, c (Å)8.867 (1), 4.8579 (2), 29.390 (2)
β (°) 96.05 (1)
V3)1258.9 (2)
Z4
Radiation typeMo Kα
µ (mm1)2.52
Crystal size (mm)0.32 × 0.30 × 0.12
Data collection
DiffractometerSiemens SMART 1K CCD area detector
diffractometer
Absorption correctionIntegration
(XPREP in SHELXTL; Sheldrick, 1995), before correction Rint = 0.080
Tmin, Tmax0.520, 0.752
No. of measured, independent and
observed [I > 2σ(I)] reflections
10880, 3316, 3136
Rint0.027
(sin θ/λ)max1)0.682
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.029, 0.058, 1.30
No. of reflections3316
No. of parameters136
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.60, 0.83

Computer programs: SMART (Siemens, 1996), SMART, SAINT (Siemens, 1996), SHELXTL (Sheldrick, 1995), SHELXTL.

Selected geometric parameters (Å, º) top
I—C182.053 (3)C3—N41.473 (4)
I—N42.712 (2)N4—C51.471 (4)
O1—C61.429 (4)C5—C61.517 (4)
O1—C21.430 (4)C11—C171.438 (4)
C2—C31.518 (4)C17—C181.201 (4)
C18—I—N4177.84 (10)C5—N4—C3110.0 (2)
C6—O1—C2110.8 (2)C5—N4—I112.09 (17)
O1—C2—C3110.5 (2)C3—N4—I108.20 (16)
N4—C3—C2112.1 (2)C17—C18—I176.5 (3)
 

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