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The structure of Rb2PO3F was determined at 290 and 130 K, while that of Cs2PO3F was determined at 240 and 100 K. Both compounds belong to the [beta]-K2SO4 family. The structure analysis did not reveal signs of a phase transition in either compound. Crystal chemical considerations do not favour the presence of a phase transition in either Rb2PO3F or Cs2PO3F. However, glass-like phase transitions were observed by differential scanning calorimetry in slightly humid samples at 175 and 177 K for Rb2PO3F and Cs2PO3F, respectively, but were not observed in well dried samples. The bond distances are normal and Cs2PO3F is twinned.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106016350/sq3009sup1.cif
Contains datablocks global, I_290, I_130, II_240, II_100

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106016350/sq3009I_290sup2.hkl
Contains datablock I_290

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106016350/sq3009I_130sup3.hkl
Contains datablock I_130

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106016350/sq3009II_240sup4.hkl
Contains datablock II_240

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106016350/sq3009II_100sup5.hkl
Contains datablock II_100

Comment top

Interest in these compounds was generated by a previous analysis of the members of the β-K2SO4 family with simple (non-complex) cations (Fábry & Pérez-Mato, 1993) [see also Beznosikov (1993) and da Silva et al. (2005)]. This analysis resulted in the setting of criteria that enable qualitative distinction of the simple-cation members of the β-K2SO4 family that undergo low-temperature phase transitions from the stable phases.

There are two symmetry-independent cations in the structures belonging to the β-K2SO4 family. The cation that is surrounded by 11 (or ten) anionic ligands (i.e. O atoms in the prototypic compound β-K2SO4) is less firmly bound than that with nine closest neighbours. The former cation will be hereafter called M11. Low-temperature phase transitions occur in those structures where the cation M11 is significantly underbonded (Brown, 1992). Typically, the underbonding of this cation is accompanied by the presence of a very short cation–anion ligand interaction. Hereafter, this short interaction will be denominated as C1. C1 is often the shortest cation–anion interaction in β-K2SO4 structures. Its contribution to the overall bond-valence sum tends to be high in the compounds where the low-temperature phase transitions occur. The shortening of C1 is significant with regard to the sum of the ionic radii (Shannon, 1976).

C1 is approximately parallel to the unit-cell parameter a in the Pnma setting (Fig. 1). Therefore the unit-cell ratios a/b and a/c also correlate with occurrences of the low-temperature phase transitions in this compound.

This is shown in Fig. 2, which depicts the plot of a/b and a/c unit-cell ratios for the title and related compounds. K2SeO4 and Tl2SeO4 are representatives of the β-K2SO4 structures with confirmed low-temperature phase transitions (Yamada et al., 1984; Friese et al., 2004, respectively). One of these compounds is situated towards the left corner of the plot and the other lies well below the dashed line. This line depicts the loci that conform to the orthohexagonal metric of the unit cell, i.e. the loci for which the condition c = b1/2 is fulfilled; the shorter the ratio, the more probable the low-temperature phase transitions. It can also be seen that the majority of the compounds are situated below the dashed line. The plot shows a certain regularity in the positions of the compounds either with corresponding cations or corresponding anions. For example, it can be seen that Tl compounds tend to be situated below the respective Cs compounds with the same anion, and that there is a similar tendency for the positions of the K, Rb and Cs compounds with the same anion. (A hypothetical structure of Tl2PO3F would be in the vicinity of a/b 1.31 and a/c 0.736, i.e. in the region where a low-temperature phase transition can be expected.) Tables 1 and 2 list the numerical values of the criteria given above.

It follows from Fig. 2 that the flouorotrioxophosphates are unusual in their positions, especially in K2PO3F. Two opposite criteria are present; it is situated on the left side, but it is also situated above the dashed line. By analogy to the selenates, it can be assumed that a low-temperature phase transition would be more likely in K2PO3F than in Rb2PO3F and even in Cs2PO3F. [In K2PO3F, no phase transition was detected by a differential scanning calorimetry experiment (Vaněk, 2004) in the temperature region 96–483 K.]

The reason for the unusual positions of the fluorotrioxophosphates is plausibly related to the size and symmetry of the [PO3F]2− anion. The P—F bond distance is longer than the P—O bond lengths. It is of interest that in K2PO3F (Payen et al., 1979), as well as in the title structures, the C1 interaction involves the F atom. On the other hand, the longer bond P—F is accommodated in the structure by a significantly larger deviation of C1 from parallelism with the a axis (cf. Fig. 1 and Table 2.)

We were interested in confirming the hypothesis that Rb2PO3F and Cs2PO3F belong to the β-K2SO4 family and that fluorine is involved in the C1 interaction. It has also been of interest to find the deviation of C1 from being parallel to the a axis. Although low-temperature phase transitions were not expected, we still carried out differential-scanning calorimetry experiments.

In carefully dried samples of either compound, no phase transitions were observed by differential scanning calorimetry. However, even in slightly humid samples (the title compounds are hygroscopic), phase transitions were observed at 175 and 177 K for Rb2PO3F and Cs2PO3F, respectively. The measured enthalpies were not reproducible. The structure determinations did not reveal signs of phase transitions in either compound.

The influence of humidity can perhaps be related to contradictory reports on the phase transition in K2SO4. Gesi et al. (1982) observed a phase transition in K2SO4 at 56 K by dielectric measurements; Ahmed (1996) confirmed the presence of the phase transition at this temperature by powder diffraction. The low-temperature phase is monoclinic (P21/n11). It should be noted that the latter author had recrystallized the sample and had dried it before the preparation of the powder for the diffraction experiment. On the other hand, Ojima et al. (1995) did not observe any phase transition down to 15 K by single-crystal diffractometry.

The interatomic distances are normal in the title structures. As expected, the C1 interaction involves fluorine in both compounds.

The twinning in Cs2PO3F is remarkable. It is related to the lattice parameters b and c. The ratio c/b is ~ 31/2 and mimics orthohexagonal lattice parameters. The approximation of the lattice parameters b and c to the orthohexagonal metric in Cs2PO3F could be predicted taking into account the positions of the related compounds in Fig. 1. The lattice parameters as well as their ratios in the β-K2SO4 family are dependent on the constituent ions, thus confirming the ionic character of these compounds (Aleksovska et al., 1998). It is also of interest that only two and not three domain states were observed. Details regarding the twinning are given in the CIF for both determinations of Cs2PO3F.

We have also synthesized Tl2PO3F and determined its structure. It was found that it belongs to an unprecedented new structural type with a space-group type R3 or R3. The structure determination will be published in the near future.

Experimental top

The structures were prepared by neutralization of stoichiometric amounts of Rb2CO3 (3.0375 g, 0.013153 mol) or Cs2CO3 (4.2855 g, 0.013153 mol) and H2PO3F. H2PO3F was obtained from a solution of (NH4)2PO3F·H2O (2 g, 0.013153 mol) that was passed through a catex column. (NH4)2PO3F·H2O was prepared by the method described by Schülke & Kayser (1991), and the raw material of (NH4)2PO3F·H2O prepared by this method was recrystallized in order to remove contamination of NH4H2PO4. The volume of the eluted solution of H2PO3F was about 120 ml in both cases. The solutions were put into an evacuated desiccator over P4O10. Crystals appeared within one week. Technical details of the calorimetric experiments are provided in the CIF. For K2PO3F, no anomaly was found in the temperature region 96–483 K. 20 measurements of Rb2PO3F and 24 measurements of Cs2PO3F were carried out in the temperature region 96–433 K for six different samples of each compound. A reproducible and a reversible glassy-like phase transition took place at 175 K for Rb2PO3F and 177 K for Cs2PO3F, with varying value of ΔCp, unless the sample was carefully dried and placed in an aluminium pan in a dry-box.

Computing details top

Data collection: COLLECT (Hooft, 1998) for I_290, I_130; CrysAlis CCD (Oxford Diffraction, 2005) for II_240, II_100. Cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997) for I_290, I_130; CrysAlis RED (Oxford Diffraction, 2005) for II_240, II_100. Data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK for I_290, I_130; CrysAlis RED for II_240, II_100. For all compounds, program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: JANA2000 (Petříček et al., 2000). Molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) for I_290. For all compounds, software used to prepare material for publication: JANA2000.

Figures top
[Figure 1] Fig. 1. View of the unit cell of Rb2PO3F at 290 K (Farrugia, 1997). The displacement parameters are at the 50% probability level. The C1 interaction is shown. (The structures of Cs2PO3F are virtually the same.)
[Figure 2] Fig. 2. Lattice parameter ratios a/b versus a/c for selected β-K2SO4 compounds (Pnma setting). The dashed line depicts the loci of the unit cells with orthohexagonal metric. The same symbols are applied for the compounds with the same cations. K2SeO4 and Tl2SeO4 undergo confirmed low-temperature phase transitions (Origin6.1; OriginLab Corporation, 2000).
(I_290) Dirubidium fluorotrioxophosphate top
Crystal data top
Rb2PO3F10 images collected for cell determiantion. Detector distance: 40 mm for cell determination. Rotation per frame: 1 deg for cell determination. Generator setting: 50 kV/20mA.
Mr = 268.9Dx = 3.514 (1) Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ac 2nCell parameters from 3814 reflections
a = 7.8714 (2) Åθ = 1.0–27.5°
b = 6.1236 (2) ŵ = 19.49 mm1
c = 10.5424 (3) ÅT = 290 K
V = 508.16 (3) Å3Prism, colourless
Z = 40.18 × 0.15 × 0.12 mm
F(000) = 488
Data collection top
Nonius KappaCCD
diffractometer
630 independent reflections
Radiation source: fine-focus sealed tube570 reflections with I > 3σ(I)
Graphite monochromatorRint = 0.079
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.2°
Rotation method data acquisition using ω scansh = 1010
Absorption correction: gaussian
(Coppens, 1970)
k = 77
Tmin = 0.073, Tmax = 0.173l = 1313
7793 measured reflections
Refinement top
Refinement on F0 constraints
R[F2 > 2σ(F2)] = 0.018Weighting scheme based on measured s.u.'s w = 1/[σ2(F) + 0.0004F2]
wR(F2) = 0.030(Δ/σ)max = 0.008
S = 1.21Δρmax = 0.65 e Å3
630 reflectionsΔρmin = 0.46 e Å3
41 parametersExtinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
0 restraintsExtinction coefficient: 0.132 (12)
Crystal data top
Rb2PO3FV = 508.16 (3) Å3
Mr = 268.9Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 7.8714 (2) ŵ = 19.49 mm1
b = 6.1236 (2) ÅT = 290 K
c = 10.5424 (3) Å0.18 × 0.15 × 0.12 mm
Data collection top
Nonius KappaCCD
diffractometer
630 independent reflections
Absorption correction: gaussian
(Coppens, 1970)
570 reflections with I > 3σ(I)
Tmin = 0.073, Tmax = 0.173Rint = 0.079
7793 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01841 parameters
wR(F2) = 0.0300 restraints
S = 1.21Δρmax = 0.65 e Å3
630 reflectionsΔρmin = 0.46 e Å3
Special details top

Experimental. The calorimetric experiments were performed on a differential scanning calorimeter Perkin Elmer DSC 7, Pyris Software [Perkin Elmer Instruments (2001). Pyris Software. Version 4.02. Perkin Elmer Instruments, 710 Bridgeport Avenue, Shelton, CT 06484–4794, USA] for measurements below 290 K while for measurements above 290 K a differential scanning calorimeter Perkin Elmer Pyris Diamond DSC, Pyris Software (PerkinElmer Instruments, 2001) was used.

The sample masses: 30±10 mg; scanning rate 10 K/min, aluminium 40 µl or 30 µ pans. ?

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Rb10.17362 (5)0.250.08089 (3)0.02586 (15)
Rb20.00298 (5)0.250.71819 (3)0.02500 (15)
P0.24073 (12)0.250.41616 (7)0.0174 (3)
O10.3059 (4)0.250.5501 (3)0.0303 (9)
O20.2759 (3)0.0447 (3)0.34441 (17)0.0357 (7)
F0.0372 (3)0.250.4316 (3)0.0473 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Rb10.0254 (3)0.0261 (3)0.0260 (3)00.00001 (14)0
Rb20.0246 (3)0.0281 (3)0.0223 (3)00.00084 (13)0
P0.0175 (5)0.0179 (5)0.0167 (4)00.0001 (3)0
O10.0335 (16)0.0342 (16)0.0231 (13)00.0081 (12)0
O20.0495 (14)0.0255 (10)0.0321 (10)0.0046 (10)0.0011 (10)0.0092 (8)
F0.0187 (13)0.079 (2)0.0444 (17)00.0015 (11)0
Geometric parameters (Å, º) top
P—O11.502 (3)Rb1—O2i3.1539 (19)
P—O21.493 (2)Rb1—F3.850 (3)
P—O2i1.493 (2)Rb1—Fvii2.865 (3)
P—F1.610 (3)Rb2—O12.971 (3)
Rb1—O1ii3.207 (3)Rb2—O1viii2.894 (3)
Rb1—O1iii3.0832 (3)Rb2—O2ix2.918 (2)
Rb1—O1iv3.0832 (3)Rb2—O2x2.838 (2)
Rb1—O23.1539 (19)Rb2—O2xi2.838 (2)
Rb1—O2ii3.464 (3)Rb2—O2xii2.918 (2)
Rb1—O2iii3.1031 (19)Rb2—F3.034 (3)
Rb1—O2v3.1031 (19)Rb2—Fix3.4593 (14)
Rb1—O2vi3.464 (3)Rb2—Fxiii3.4593 (14)
O1—P—O2114.37 (10)O2—P—F103.63 (12)
O1—P—O2i114.37 (10)O2i—P—O2114.70 (12)
O1—P—F104.19 (16)O2i—P—F103.63 (12)
O2—P—O2i114.70 (12)
Symmetry codes: (i) x, y+1/2, z; (ii) x1/2, y, z+1/2; (iii) x+1/2, y, z1/2; (iv) x+1/2, y+1, z1/2; (v) x+1/2, y+1/2, z1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y, z+1/2; (viii) x1/2, y, z+3/2; (ix) x, y, z+1; (x) x+1/2, y, z+1/2; (xi) x+1/2, y+1/2, z+1/2; (xii) x, y+1/2, z+1; (xiii) x, y+1, z+1.
(I_130) Di-rubidium fluorotrioxophosphate top
Crystal data top
Rb2PO3FF(000) = 488
Mr = 268.9Dx = 3.560 (1) Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ac 2nCell parameters from 4214 reflections
a = 7.8403 (2) Åθ = 1–27.5°
b = 6.1034 (2) ŵ = 19.75 mm1
c = 10.4813 (3) ÅT = 130 K
V = 501.56 (3) Å3Prism, colourless
Z = 40.18 × 0.15 × 0.12 mm
Data collection top
Nonius KappaCCD
diffractometer
623 independent reflections
Radiation source: fine-focus sealed tube581 reflections with I > 3σ(I)
Graphite monochromatorRint = 0.084
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.2°
Rotation method data acquisition using ω scansh = 1010
Absorption correction: gaussian
(Coppens, 1970)
k = 77
Tmin = 0.067, Tmax = 0.179l = 1313
7775 measured reflections
Refinement top
Refinement on F0 constraints
R[F2 > 2σ(F2)] = 0.021Weighting scheme based on measured s.u.'s w = 1/[σ2(F) + 0.0004F2]
wR(F2) = 0.033(Δ/σ)max = 0.010
S = 1.39Δρmax = 0.83 e Å3
623 reflectionsΔρmin = 0.71 e Å3
41 parametersExtinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
0 restraintsExtinction coefficient: 0.111 (12)
Crystal data top
Rb2PO3FV = 501.56 (3) Å3
Mr = 268.9Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 7.8403 (2) ŵ = 19.75 mm1
b = 6.1034 (2) ÅT = 130 K
c = 10.4813 (3) Å0.18 × 0.15 × 0.12 mm
Data collection top
Nonius KappaCCD
diffractometer
623 independent reflections
Absorption correction: gaussian
(Coppens, 1970)
581 reflections with I > 3σ(I)
Tmin = 0.067, Tmax = 0.179Rint = 0.084
7775 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02141 parameters
wR(F2) = 0.0330 restraints
S = 1.39Δρmax = 0.83 e Å3
623 reflectionsΔρmin = 0.71 e Å3
Special details top

Experimental. The calorimetric experiments were performed on a differential scanning calorimeter Perkin Elmer DSC 7, Pyris Software [Perkin Elmer Instruments (2001). Pyris Software. Version 4.02. Perkin Elmer Instruments, 710 Bridgeport Avenue, Shelton, CT 06484–4794, USA] for measurements below 290 K while for measurements above 290 K a differential scanning calorimeter Perkin Elmer Pyris Diamond DSC, Pyris Software (PerkinElmer Instruments, 2001) was used.

The sample masses: 30±10 mg; scanning rate 10 K/min, aluminium 40 µl or 30 µ pans. ?

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Rb20.00450 (5)0.250.71800 (3)0.01349 (16)
Rb10.17204 (5)0.250.07970 (3)0.01320 (16)
P0.24068 (14)0.250.41541 (8)0.0100 (3)
O10.3079 (4)0.250.5505 (3)0.0159 (8)
O20.2729 (3)0.0427 (3)0.34255 (18)0.0191 (6)
F0.0349 (3)0.250.4337 (3)0.0243 (9)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Rb20.0140 (3)0.0142 (3)0.0122 (3)00.00057 (13)0
Rb10.0131 (3)0.0129 (3)0.0136 (3)00.00027 (13)0
P0.0101 (5)0.0097 (5)0.0101 (5)00.0002 (3)0
O10.0181 (15)0.0162 (16)0.0136 (13)00.0036 (11)0
O20.0260 (11)0.0138 (10)0.0175 (9)0.0020 (9)0.0009 (8)0.0038 (8)
F0.0104 (13)0.0422 (18)0.0203 (14)00.0000 (10)0
Geometric parameters (Å, º) top
P—O11.511 (3)Rb1—O2i3.133 (2)
P—O21.499 (2)Rb1—F3.863 (3)
P—O2i1.499 (2)Rb1—Fvii2.848 (3)
P—F1.625 (3)Rb2—O12.956 (3)
Rb1—O1ii3.164 (3)Rb2—O1viii2.875 (3)
Rb1—O1iii3.0710 (3)Rb2—O2ix2.885 (2)
Rb1—O1iv3.0710 (3)Rb2—O2x2.818 (2)
Rb1—O23.133 (2)Rb2—O2xi2.818 (2)
Rb1—O2ii3.472 (2)Rb2—O2xii2.885 (2)
Rb1—O2iii3.091 (2)Rb2—F2.989 (3)
Rb1—O2v3.091 (2)Rb2—Fix3.4550 (13)
Rb1—O2vi3.472 (2)Rb2—Fxiii3.4550 (13)
O1—P—O2114.75 (10)O2—P—F103.15 (11)
O1—P—O2i114.75 (10)O2i—P—O2115.10 (12)
O1—P—F103.63 (15)O2i—P—F103.15 (11)
O2—P—O2i115.10 (12)
Symmetry codes: (i) x, y+1/2, z; (ii) x1/2, y, z+1/2; (iii) x+1/2, y, z1/2; (iv) x+1/2, y+1, z1/2; (v) x+1/2, y+1/2, z1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y, z+1/2; (viii) x1/2, y, z+3/2; (ix) x, y, z+1; (x) x+1/2, y, z+1/2; (xi) x+1/2, y+1/2, z+1/2; (xii) x, y+1/2, z+1; (xiii) x, y+1, z+1.
(II_240) Dicaesium fluorotrioxophosphate top
Crystal data top
Cs2PO3FThe sample is hygroscopic and therefore the crystal was put into the silicon grease. The worse standard uncertainties of the lattice parameters with regard to the measurement at 100 K is difficult to explain.
Mr = 363.8Dx = 4.129 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ac 2nCell parameters from 9848 reflections
a = 8.308 (2) Åθ = 3.1–26.9°
b = 6.3812 (9) ŵ = 12.66 mm1
c = 11.036 (2) ÅT = 240 K
V = 585.07 (19) Å3Prism elongated along a, colourless
Z = 40.25 × 0.10 × 0.03 mm
F(000) = 632
Data collection top
Oxford Diffraction Model?? CCD
diffractometer
974 independent reflections
Radiation source: Enhance (Mo) X-ray Source832 reflections with I > 3σ(I)
Graphite monochromatorRint = 0.041
Detector resolution: 8.3438 pixels mm-1θmax = 26.9°, θmin = 3.1°
ω scansh = 1010
Absorption correction: analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
k = 88
Tmin = 0.168, Tmax = 0.460l = 1313
6666 measured reflections
Refinement top
Refinement on F0 constraints
R[F2 > 2σ(F2)] = 0.022Weighting scheme based on measured s.u.'s w = 1/[σ2(F) + 0.0004F2]
wR(F2) = 0.037(Δ/σ)max = 0.007
S = 1.48Δρmax = 0.58 e Å3
974 reflectionsΔρmin = 0.71 e Å3
42 parametersExtinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
0 restraintsExtinction coefficient: 0.061 (6)
Crystal data top
Cs2PO3FV = 585.07 (19) Å3
Mr = 363.8Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 8.308 (2) ŵ = 12.66 mm1
b = 6.3812 (9) ÅT = 240 K
c = 11.036 (2) Å0.25 × 0.10 × 0.03 mm
Data collection top
Oxford Diffraction Model?? CCD
diffractometer
974 independent reflections
Absorption correction: analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
832 reflections with I > 3σ(I)
Tmin = 0.168, Tmax = 0.460Rint = 0.041
6666 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02242 parameters
wR(F2) = 0.0370 restraints
S = 1.48Δρmax = 0.58 e Å3
974 reflectionsΔρmin = 0.71 e Å3
Special details top

Experimental. The calorimetric experiments were performed on a differential scanning calorimeter Perkin Elmer DSC 7, Pyris Software [Perkin Elmer Instruments (2001). Pyris Software. Version 4.02. Perkin Elmer Instruments, 710 Bridgeport Avenue, Shelton, CT 06484–4794, USA] for measurements below 290 K while for measurements above 290 K a differential scanning calorimeter Perkin Elmer Pyris Diamond DSC, Pyris Software (PerkinElmer Instruments, 2001) was used.

The sample masses: 30±10 mg; scanning rate 10 K/min, aluminium 40 µl or 30 µ pans. ?

Refinement. The structure is a twin composed of two domain states. The twinning is presumably related to the ratio of the lattice parameters c/b (1.7295) that is very close to the ratio of the unit-cell parameters of the orthohexagonal unit cell (3)1/2. Since the observed twinning at two cases contained only two domain states, and not three, the twinning is assumed not to be caused by rotation of the lattices pertinent to each respective domain by 120º but rather is assumed to be reflection through the plane (011).

The twinning matrix relating the minor and dominating states (denoted with indices "m" and "d", respectively) is:

(1 0 0) (am,bm,cm)=(ad,bd,cd)(0 1–2cos2ϕ −2sin2ϕ) (0 − 2cos2ϕ 1–2sin2ϕ)

where ϕ=arctg(c/b).

This means that for the transformation equation is: (1 0 0) (am,bm,cm)=(ad,bd,cd)(0 0.4989 − 1.4989) (0 − 0.5011 − 0.4989)

The values of the matrix differ only minutely (\sim1/1000) from the pertinent values regarding rotation by 120º:

(1 0 0) (am,bm,cm)=(ad,bd,cd)(0 0.5 − 1.5) (0 − 0.5 − 1/2)

The idealized transformation is thus:

(1 0 0) (am,bm,cm)=(ad,bd,cd)(0 0.5 − 1.5) (0 − 0.5 − 1/2)

The refinement with idealized twinning matrix resulted in the same indicators of the refinement as with the non-idealized matrix given above. (This contrasts to the refinement at 100 K.)

The overlapped diffractions hkl are satisfying the condition k+l=2n. For the refinement there were used the overlapped diffractions and the non-overlapped diffractions pertinent to the dominating domain state.

The refined volume proportion of the minor domain equalled to: 0.135 (1).

The difference electron density given in _refine_diff_density_max and _refine_diff_density_min was calculated with the help of the formula Fobscorr=Fobs*(Fcalc1/Fcalc);

The alternative calculation with Fobs=sqrt(Fobs2-Fcalc,m2) yielded the following results: ρmax=0.73, ρmin=-0.68 e Å−3.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cs10.17416 (5)0.250.08366 (4)0.02138 (15)
Cs20.00153 (5)0.250.71578 (4)0.02044 (16)
P0.2453 (2)0.250.41694 (15)0.0148 (4)
O10.2985 (6)0.250.5465 (4)0.0251 (15)
O20.2828 (5)0.0509 (6)0.3494 (3)0.0289 (11)
F0.0521 (5)0.250.4245 (5)0.0386 (17)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cs10.0235 (3)0.0196 (3)0.0210 (3)00.00055 (18)0
Cs20.0204 (3)0.0223 (3)0.0186 (3)00.00077 (16)0
P0.0154 (7)0.0136 (8)0.0153 (8)00.0007 (7)0
O10.031 (3)0.027 (3)0.017 (3)00.004 (2)0
O20.040 (2)0.0216 (18)0.0253 (19)0.0038 (17)0.0004 (18)0.0067 (15)
F0.018 (2)0.062 (4)0.036 (3)00.001 (2)0
Geometric parameters (Å, º) top
P—O11.496 (5)Cs1—O2i3.321 (4)
P—O21.506 (4)Cs1—F3.896 (5)
P—O2i1.506 (4)Cs1—Fvii3.141 (4)
P—F1.608 (5)Cs2—O13.115 (5)
Cs1—O1ii3.435 (5)Cs2—O1viii3.105 (5)
Cs1—O1iii3.2249 (7)Cs2—O2ix3.109 (4)
Cs1—O1iv3.2249 (7)Cs2—O2x3.027 (4)
Cs1—O23.321 (4)Cs2—O2xi3.027 (4)
Cs1—O2ii3.568 (4)Cs2—O2xii3.109 (4)
Cs1—O2iii3.240 (4)Cs2—F3.245 (5)
Cs1—O2v3.240 (4)Cs2—Fix3.571 (2)
Cs1—O2vi3.568 (4)Cs2—Fxiii3.571 (2)
O1—P—O2114.31 (17)O2—P—F103.43 (19)
O1—P—O2i114.31 (17)O2i—P—O2115.1 (2)
O1—P—F104.2 (3)O2i—P—F103.43 (19)
O2—P—O2i115.1 (2)
Symmetry codes: (i) x, y+1/2, z; (ii) x1/2, y, z+1/2; (iii) x+1/2, y, z1/2; (iv) x+1/2, y+1, z1/2; (v) x+1/2, y+1/2, z1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y, z+1/2; (viii) x1/2, y, z+3/2; (ix) x, y, z+1; (x) x+1/2, y, z+1/2; (xi) x+1/2, y+1/2, z+1/2; (xii) x, y+1/2, z+1; (xiii) x, y+1, z+1.
(II_100) Dicaesium fluorotrioxophosphate top
Crystal data top
Cs2PO3FF(000) = 632
Mr = 363.8Dx = 4.177 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ac 2nCell parameters from 9972 reflections
a = 8.2821 (8) Åθ = 3.1–26.6°
b = 6.3577 (6) ŵ = 12.81 mm1
c = 10.9827 (8) ÅT = 100 K
V = 578.30 (9) Å3Prism elongated along a, colourless
Z = 40.25 × 0.09 × 0.03 mm
Data collection top
Oxford Diffraction Mode ?? CCD
diffractometer
939 independent reflections
Radiation source: Enhance (Mo) X-ray Source849 reflections with I > 3σ(I)
Graphite monochromatorRint = 0.038
Detector resolution: 8.3438 pixels mm-1θmax = 26.6°, θmin = 3.7°
ω scansh = 1010
Absorption correction: analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
k = 77
Tmin = 0.161, Tmax = 0.434l = 1313
6856 measured reflections
Refinement top
Refinement on F0 constraints
R[F2 > 2σ(F2)] = 0.017Weighting scheme based on measured s.u.'s w = 1/[σ2(F) + 0.0004F2]
wR(F2) = 0.036(Δ/σ)max = 0.014
S = 1.52Δρmax = 0.37 e Å3
939 reflectionsΔρmin = 0.41 e Å3
42 parametersExtinction correction: B-C type 1 Lorentzian isotropic (Becker & Coppens, 1974)
0 restraintsExtinction coefficient: 0.040 (5)
Crystal data top
Cs2PO3FV = 578.30 (9) Å3
Mr = 363.8Z = 4
Orthorhombic, PnmaMo Kα radiation
a = 8.2821 (8) ŵ = 12.81 mm1
b = 6.3577 (6) ÅT = 100 K
c = 10.9827 (8) Å0.25 × 0.09 × 0.03 mm
Data collection top
Oxford Diffraction Mode ?? CCD
diffractometer
939 independent reflections
Absorption correction: analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
849 reflections with I > 3σ(I)
Tmin = 0.161, Tmax = 0.434Rint = 0.038
6856 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01742 parameters
wR(F2) = 0.0360 restraints
S = 1.52Δρmax = 0.37 e Å3
939 reflectionsΔρmin = 0.41 e Å3
Special details top

Experimental. The calorimetric experiments were performed on a differential scanning calorimeter Perkin Elmer DSC 7, Pyris Software [Perkin Elmer Instruments (2001). Pyris Software. Version 4.02. Perkin Elmer Instruments, 710 Bridgeport Avenue, Shelton, CT 06484–4794, USA] for measurements below 290 K while for measurements above 290 K a differential scanning calorimeter Perkin Elmer Pyris Diamond DSC, Pyris Software (PerkinElmer Instruments, 2001) was used.

The sample masses: 30±10 mg; scanning rate 10 K/min, aluminium 40 µl or 30 µ pans. ?

Refinement. The structure is a twin composed of two domain states. The twinning is presumably related to the ratio of the lattice parameters c/b (1.7295) that is very close to the ratio of the unit-cell parameters of the orthohexagonal unit cell (3)1/2. Since the observed twinning at two cases contained only two domain states, and not three, the twinning is assumed not to be caused by rotation of the lattices pertinent to each respective domain by 120º but rather it is assumed to be reflection through the plane (011).

The twinning matrix relating the minor and dominating states (denoted with indices "m" and "d", respectively) is: (1 0 0) (am,bm,cm)=(ad,bd,cd)(0 1–2cos2ϕ −2sin2ϕ) (0 − 2cos2ϕ 1–2sin2ϕ)

where ϕ=arctg(c/b).

The absolute values of the numerical values of the elements with goniometric functions differ only minutely (2/1000) from the pertinent values of the elements of the rotation matrix with rotation by 120º. Nevertheless, in difference to the refinement at 240 K the twinning matrix that was applied was

(1 0 0) (am,bm,cm)=(ad,bd,cd)(0 0.5 − 1.5) (0 − 0.5 − 1/2)

and not

(1 0 0) (am,bm,cm)=(ad,bd,cd)(0 0.4980 − 1.4980) (0 − 0.5020 − 0.4980)

because the indicators of refinement in the latter case were worse.

The overlapped diffractions hkl are satisfying the condition k+l=2n. For the refinement there were used the overlapped diffractions and the non overlapped diffractions pertinent to the dominating domain state.

The refined volume proportion of the minor domain equalled to: 0.135 (1).

The difference electron density given in _refine_diff_density_max and _refine_diff_density_min was calculated with the help of the formula Fobscorr=Fobs*(Fcalc1/Fcalc);

The alternative calculation with Fobs=sqrt(Fobs2-Fcalc,m2) yielded the following results: ρmax=0.71, ρmin=-0.69 e Å−3.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Cs10.17283 (4)0.250.08342 (3)0.00966 (15)
Cs20.00169 (4)0.250.71520 (4)0.00956 (15)
P0.2464 (2)0.250.41686 (13)0.0072 (4)
O10.2984 (6)0.250.5490 (4)0.0134 (13)
O20.2825 (4)0.0483 (5)0.3489 (3)0.0143 (9)
F0.0491 (5)0.250.4253 (4)0.0184 (13)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cs10.0092 (2)0.0093 (3)0.0106 (3)00.00006 (14)0
Cs20.0084 (3)0.0107 (3)0.0096 (2)00.00066 (13)0
P0.0071 (7)0.0055 (8)0.0091 (8)00.0003 (6)0
O10.013 (2)0.015 (2)0.013 (2)00.0023 (19)0
O20.0180 (15)0.0105 (15)0.0145 (16)0.0033 (14)0.0021 (14)0.0048 (12)
F0.0076 (18)0.032 (2)0.016 (2)00.0014 (16)0
Geometric parameters (Å, º) top
P—O11.514 (5)Cs1—O2i3.312 (3)
P—O21.513 (3)Cs1—F3.892 (4)
P—O2i1.513 (3)Cs1—Fvii3.118 (4)
P—F1.637 (4)Cs2—O13.083 (5)
Cs1—O1ii3.425 (5)Cs2—O1viii3.073 (5)
Cs1—O1iii3.2101 (6)Cs2—O2ix3.082 (3)
Cs1—O1iv3.2101 (6)Cs2—O2x3.008 (3)
Cs1—O23.312 (3)Cs2—O2xi3.008 (3)
Cs1—O2ii3.556 (3)Cs2—O2xii3.082 (3)
Cs1—O2iii3.220 (3)Cs2—F3.212 (4)
Cs1—O2v3.220 (3)Cs2—Fix3.5551 (17)
Cs1—O2vi3.556 (3)Cs2—Fxiii3.5551 (17)
O1—P—O2114.64 (15)O2—P—F102.99 (16)
O1—P—O2i114.64 (15)O2i—P—O2115.82 (19)
O1—P—F103.3 (2)O2i—P—F102.99 (16)
O2—P—O2i115.82 (19)
Symmetry codes: (i) x, y+1/2, z; (ii) x1/2, y, z+1/2; (iii) x+1/2, y, z1/2; (iv) x+1/2, y+1, z1/2; (v) x+1/2, y+1/2, z1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y, z+1/2; (viii) x1/2, y, z+3/2; (ix) x, y, z+1; (x) x+1/2, y, z+1/2; (xi) x+1/2, y+1/2, z+1/2; (xii) x, y+1/2, z+1; (xiii) x, y+1, z+1.

Experimental details

(I_290)(I_130)(II_240)(II_100)
Crystal data
Chemical formulaRb2PO3FRb2PO3FCs2PO3FCs2PO3F
Mr268.9268.9363.8363.8
Crystal system, space groupOrthorhombic, PnmaOrthorhombic, PnmaOrthorhombic, PnmaOrthorhombic, Pnma
Temperature (K)290130240100
a, b, c (Å)7.8714 (2), 6.1236 (2), 10.5424 (3)7.8403 (2), 6.1034 (2), 10.4813 (3)8.308 (2), 6.3812 (9), 11.036 (2)8.2821 (8), 6.3577 (6), 10.9827 (8)
V3)508.16 (3)501.56 (3)585.07 (19)578.30 (9)
Z4444
Radiation typeMo KαMo KαMo KαMo Kα
µ (mm1)19.4919.7512.6612.81
Crystal size (mm)0.18 × 0.15 × 0.120.18 × 0.15 × 0.120.25 × 0.10 × 0.030.25 × 0.09 × 0.03
Data collection
DiffractometerNonius KappaCCD
diffractometer
Nonius KappaCCD
diffractometer
Oxford Diffraction Model?? CCD
diffractometer
Oxford Diffraction Mode ?? CCD
diffractometer
Absorption correctionGaussian
(Coppens, 1970)
Gaussian
(Coppens, 1970)
Analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
Analytical
CrysAlis RED (Oxford Diffraction, 2005). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by Clark & Reid (1995).
Tmin, Tmax0.073, 0.1730.067, 0.1790.168, 0.4600.161, 0.434
No. of measured, independent and
observed [I > 3σ(I)] reflections
7793, 630, 570 7775, 623, 581 6666, 974, 832 6856, 939, 849
Rint0.0790.0840.0410.038
(sin θ/λ)max1)0.6490.6490.6360.629
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.030, 1.21 0.021, 0.033, 1.39 0.022, 0.037, 1.48 0.017, 0.036, 1.52
No. of reflections630623974939
No. of parameters41414242
Δρmax, Δρmin (e Å3)0.65, 0.460.83, 0.710.58, 0.710.37, 0.41

Computer programs: COLLECT (Hooft, 1998), CrysAlis CCD (Oxford Diffraction, 2005), HKL SCALEPACK (Otwinowski & Minor, 1997), CrysAlis RED (Oxford Diffraction, 2005), HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK, CrysAlis RED, SIR97 (Altomare et al., 1999), JANA2000 (Petříček et al., 2000), ORTEP-3 for Windows (Farrugia, 1997), JANA2000.

Some stereochemical parameters regarding selected compounds of the β-K2SO4 family: C1: Length (Å) of the interaction C1; C1/CR: the ratio of C1 to the sum of crystal radii (Shannon, 1976); M11(bv): bond valence of M11 (Brese & O'Keeffe (1991); Sum: bond valence sum of the cation M11; M11(bv)/Sum ???? top
CompoundC1C1/CRM11(bv)SumM11(bv)/Sum
K2SO4a2.714 (2)0.9020.2065 (13)1.0795 (18)0.191 (2)
K2CrO4b2.681 (1)0.8910.2256 (9)0.9358 (12)0.241 (1)
K2SeO4c2.610 (6)0.8670.273 (4)0.943 (5)0.290 (6)
K2PO3Fd2.671 (6)0.9080.159 (3)0.893 (5)0.178 (4)
Rb2SO4e2.921 (2)0.9450.1676 (11)1.0759 (17)0.156 (1)
Rb2CrO4f2.876 (15)0.9310.189 (8)0.984 (10)0.192 (8)
Rb2SeO4g2.810 (6)0.9090.228 (3)0.943 (4)0.242 (4)
Rb2PO3Fh2.865 (3)0.9490.149 (1)0.913 (2)0.163 (1)
Cs2SO4e3.177 (2)0.9780.1293 (14)1.061 (3)0.122 (2)
Cs2CrO4i3.136 (2)0.9650.1445 (9)0.968 (2)0.149 (10)
Cs2SeO4j3.038 (4)0.9350.187 (2)0.916 (3)0.204 (3)
Cs2PO3Fh3.141 (4)0.9880.1118 (13)0.901 (3)0.124 (2)
Tl2SO4k2.844 (11)0.9260.163 (5)0.838 (6)0.195 (7)
Tl2CrO4l2.70 (9)0.8790.24 (6)0.90 (6)0.27 (8)
Tl2SeO4m2.660 (18)0.8660.268 (13)0.801 (15)0.334 (2)
Notes:(a) Ojima et al. (1995); (b) Toriumi & Saito (1978); (c) González-Silgo et al. (1996); (d) Payen et al. (1979); (e) Weber et al. (1989); (f) Aleksovska et al. (1998); (g) Takahashi et al. (1987); (h) this study; (i) Morris et al. (1981); (j) Zúñiga et al. (1991); (k) Wallez et al. (2004); (l) Carter & Margulis (1972); (m) Fábry & Breczewski (1993);
Some stereochemical parameters regarding selected compounds of the β-K2SO4 family: a/b, a/c, b/c: the unit-cell ratios. M11-O/F-X: the angle (°) contatined by the atoms involved in the interaction C1 top
Compounda/ba/cb/cM11-O/F-X
K2SO4a1.2959 (3)0.74247 (6)0.5730 (1)179.7 (2)
K2CrO4b1.2945 (6)0.7374 (2)0.5696 (1)178.96 (15)
K2SeO4c1.276 (3)0.732 (2)0.573 (1)176.4 (3)
K2PO3Fd1.269 (2)0.7427 (8)0.5854 (8)166.0 (5)
Rb2SO4e1.3079 (6)0.7490 (2)0.5726 (2)179.2 (2)
Rb2CrO4f1.317 (1)0.7460 (4)0.5665 (2)178.3 (8)
Rb2SeO4g1.292 (1)0.7375 (2)0.5708 (3)179.5 (4)
Rb2PO3Fh1.28542 (8)0.74664 (4)0.58085 (4)171.6 (2)
Cs2SO4e1.3170 (7)0.7533 (3)0.5720 (2)178.7 (3)
Cs2CrO4i1.338 (1)0.7524 (8)0.5625 (5)177.70 (11)
Cs2SeO4j1.3021 (5)0.7430 (2)0.5706 (3)178.7 (3)
Cs2PO3Fh1.3020 (5)0.7528 (3)0.5782 (2)175.4 (3)
Tl2SO4k1.3182 (3)0.7352 (2)0.5577 (2)179 (7)
Tl2CrO4l1.338 (2)0.7374 (8)0.5509 (7)178 (4)
Tl2SeO4m1.3025 (8)0.7250 (4)0.5566 (3)178.1 (14)
Note: The references are the same as in Table 1.
 

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