Tetragonal caesium hydroxide monohydrate, CsOH·H
2O, a clathrate hydrate, is a polymorph of three known hexagonal or pseudo-hexagonal modifications. It was obtained as a by-product in a high-pressure experiment. Whether it is a high-pressure polymorph, however, remains to be verified. The Cs atoms are situated in cavities of the form of a bicapped pentagonal prism, within an infinite three-dimensional hydrogen-bonded oxygen framework that is locally identical to layers found in the hexagonal modifications. The Cs atom and one of the two H atoms are at sites with
symmetry, the O atom has
mm site symmetry and the second H atom has 2/
m symmetry.
Supporting information
The tetragonal modification of CsOH·H2O was initially obtained as a
by-product during the high-pressure synthesis of caesium-based ternary metal
hydrides. In the first step, binary caesium hydride powder was synthesized by
direct hydrogenation of metallic caesium ingot (STREM, 99.9%) at 700 K and 80 bar (1 bar = 10 5 Pa) hydrogen pressure for 15 d in an autoclave. In the
second step, caesium-based metal hydrides were synthesized by heating mixtures
of CsH and the corresponding metal to 800 K in a multi-anvil press at 30 kbar
pressure in air. The reaction products contained CsOH and tetragonal
CsOH·H2O as impurities. The same experiments were performed without the
metal powders, and the reaction product contained CsH, CsOH and tetragonal
CsOH·H2O. The product was white, pyrophoric and extremely sensitive to
air and moisture.
Data collection: Please give details; cell refinement: FULLPROF98 (Rodríguez-Carvajal, 1998); data reduction: FULLPROF98; program(s) used to solve structure: FOX (Favre-Nicolin & Černý, 2002); program(s) used to refine structure: FULLPROF98; molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: WinPLOTR (Roisnel & Rodríguez-Carvajal, 1998) and ATOMS.
Caesium hydroxide monohydrate
top
Crystal data top
CsOH·H2O | Dx = 3.785 (2) Mg m−3 |
Mr = 167.93 | Synchrotron radiation, λ = 0.48562 Å |
Tetragonal, I41/amd | µ = 24.21 mm−1 |
Hall symbol: -I 4bd 2 | T = 293 K |
a = 4.38088 (4) Å | Particle morphology: plate-like |
c = 15.46525 (17) Å | white |
V = 296.81 (1) Å3 | cylinder, 50 × 0.4 mm |
Z = 4 | Specimen preparation: Prepared at 800 K and 3000000 kPa |
F(000) = 332 | |
Data collection top
Two-axis goniometer diffractometer | Data collection mode: transmission |
Radiation source: synchrotron, Swiss-Norwegian Beam Line BM1B | Scan method: step |
Channel-cut Si 111 monochromator | 2θmin = 6.012°, 2θmax = 36.488°, 2θstep = 0.002° |
Specimen mounting: glass capillary | |
Refinement top
Refinement on Inet | 14 parameters |
Least-squares matrix: full with fixed elements per cycle | 0 constraints |
Rp = 0.125 | H-atom parameters not refined |
Rwp = 0.133 | Calculated w = 1/Yi |
Rexp = 0.059 | (Δ/σ)max = 0.01 |
χ2 = 5.198 | Background function: linear interpolation between 16 estimated points |
15238 data points | Preferred orientation correction: no |
Profile function: pseudo-Voigt | |
Crystal data top
CsOH·H2O | Z = 4 |
Mr = 167.93 | Synchrotron radiation, λ = 0.48562 Å |
Tetragonal, I41/amd | µ = 24.21 mm−1 |
a = 4.38088 (4) Å | T = 293 K |
c = 15.46525 (17) Å | cylinder, 50 × 0.4 mm |
V = 296.81 (1) Å3 | |
Data collection top
Two-axis goniometer diffractometer | Scan method: step |
Specimen mounting: glass capillary | 2θmin = 6.012°, 2θmax = 36.488°, 2θstep = 0.002° |
Data collection mode: transmission | |
Refinement top
Rp = 0.125 | 15238 data points |
Rwp = 0.133 | 14 parameters |
Rexp = 0.059 | H-atom parameters not refined |
χ2 = 5.198 | |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Cs | 0 | 0.75 | 0.125 | 0.0328 (5)* | |
O | 0 | 0.25 | 0.4560 (5) | 0.004 (2)* | |
H1 | 0 | 0.25 | 0.375 | 0.012* | |
H2 | 0 | 0 | 0.5 | 0.012* | |
Geometric parameters (Å, º) top
Cs—O | 3.341 (3) | Cs—Oii | 3.410 (6) |
Cs—O | 3.341 (3) | Cs—O | 3.410 (6) |
Cs—O | 3.341 (3) | Cs—O | 3.410 (6) |
Cs—O | 3.341 (3) | Cs—O | 3.410 (6) |
Cs—O | 3.341 (3) | O—Oii | 2.505 (11) |
Cs—Oi | 3.341 (3) | O—O | 2.579 (6) |
Cs—O | 3.341 (3) | O—O | 2.579 (6) |
Cs—O | 3.341 (3) | | |
| | | |
O—Cs—O | 81.92 (6) | O—Cs—O | 135.96 (17) |
O—Cs—O | 81.92 (6) | O—Cs—Oii | 135.10 (10) |
O—Cs—O | 135.96 (18) | O—Cs—O | 82.31 (13) |
O—Cs—O | 98.08 (6) | O—Cs—O | 44.90 (10) |
O—Cs—Oi | 98.08 (6) | O—Cs—O | 97.69 (13) |
O—Cs—O | 44.04 (17) | O—Cs—Oii | 82.31 (13) |
O—Cs—O | 180.0000 | O—Cs—O | 135.10 (10) |
O—Cs—Oii | 97.69 (13) | O—Cs—O | 97.69 (13) |
O—Cs—O | 44.90 (10) | O—Cs—O | 44.90 (10) |
O—Cs—O | 82.31 (13) | Oii—Cs—O | 79.93 (12) |
O—Cs—O | 135.10 (10) | Oii—Cs—O | 125.97 (7) |
O—Cs—O | 135.96 (18) | Oii—Cs—O | 125.97 (7) |
O—Cs—O | 81.92 (6) | O—Cs—O | 125.97 (7) |
O—Cs—O | 180.0000 | O—Cs—O | 125.97 (7) |
O—Cs—Oi | 44.04 (17) | O—Cs—O | 79.93 (12) |
O—Cs—O | 98.08 (6) | Oii—O—O | 121.9 (2) |
O—Cs—O | 98.08 (6) | Oii—O—O | 121.9 (2) |
O—Cs—Oii | 44.90 (10) | Oii—O—Cs | 67.98 (12) |
O—Cs—O | 97.69 (13) | Oii—O—Cs | 67.98 (12) |
O—Cs—O | 82.31 (13) | Oii—O—Csi | 67.98 (12) |
O—Cs—O | 135.10 (10) | Oii—O—Cs | 67.98 (12) |
O—Cs—O | 81.92 (6) | Oii—O—Cs | 140.03 (8) |
O—Cs—O | 44.04 (17) | Oii—O—Cs | 140.03 (8) |
O—Cs—Oi | 180.0000 | O—O—O | 116.3 (4) |
O—Cs—O | 98.08 (6) | O—O—Cs | 139.00 (6) |
O—Cs—O | 98.08 (6) | O—O—Cs | 68.96 (10) |
O—Cs—Oii | 97.69 (13) | O—O—Csi | 139.00 (6) |
O—Cs—O | 44.90 (10) | O—O—Cs | 68.96 (10) |
O—Cs—O | 135.10 (10) | O—O—Cs | 66.14 (17) |
O—Cs—O | 82.31 (13) | O—O—Cs | 66.14 (17) |
O—Cs—O | 98.08 (6) | O—O—Cs | 68.96 (10) |
O—Cs—Oi | 98.08 (6) | O—O—Cs | 139.00 (6) |
O—Cs—O | 180.0000 | O—O—Csi | 68.96 (10) |
O—Cs—O | 44.04 (17) | O—O—Cs | 139.00 (6) |
O—Cs—Oii | 44.90 (10) | O—O—Cs | 66.14 (17) |
O—Cs—O | 97.69 (13) | O—O—Cs | 66.14 (17) |
O—Cs—O | 135.10 (10) | Cs—O—Cs | 136.0 (2) |
O—Cs—O | 82.31 (13) | Cs—O—Csi | 81.92 (9) |
O—Cs—Oi | 135.96 (17) | Cs—O—Cs | 81.92 (9) |
O—Cs—O | 81.92 (6) | Cs—O—Cs | 82.31 (5) |
O—Cs—O | 81.92 (6) | Cs—O—Cs | 135.10 (12) |
O—Cs—Oii | 135.10 (10) | Cs—O—Csi | 81.92 (9) |
O—Cs—O | 82.31 (13) | Cs—O—Cs | 81.92 (9) |
O—Cs—O | 97.69 (13) | Cs—O—Cs | 135.10 (12) |
O—Cs—O | 44.90 (10) | Cs—O—Cs | 82.31 (5) |
Oi—Cs—O | 81.92 (6) | Csi—O—Cs | 136.0 (2) |
Oi—Cs—O | 81.92 (6) | Csi—O—Cs | 135.10 (12) |
Oi—Cs—Oii | 82.31 (13) | Csi—O—Cs | 82.31 (5) |
Oi—Cs—O | 135.10 (10) | Cs—O—Cs | 82.31 (5) |
Oi—Cs—O | 44.90 (10) | Cs—O—Cs | 135.10 (13) |
Oi—Cs—O | 97.69 (13) | Cs—O—Cs | 79.93 (17) |
Symmetry codes: (i) −x+1/2, y, −z+1/2; (ii) −y+1/4, −x+1/4, −z+3/4. |
Experimental details
Crystal data |
Chemical formula | CsOH·H2O |
Mr | 167.93 |
Crystal system, space group | Tetragonal, I41/amd |
Temperature (K) | 293 |
a, c (Å) | 4.38088 (4), 15.46525 (17) |
V (Å3) | 296.81 (1) |
Z | 4 |
Radiation type | Synchrotron, λ = 0.48562 Å |
µ (mm−1) | 24.21 |
Specimen shape, size (mm) | Cylinder, 50 × 0.4 |
|
Data collection |
Diffractometer | Two-axis goniometer diffractometer |
Specimen mounting | Glass capillary |
Data collection mode | Transmission |
Scan method | Step |
2θ values (°) | 2θmin = 6.012 2θmax = 36.488 2θstep = 0.002 |
|
Refinement |
R factors and goodness of fit | Rp = 0.125, Rwp = 0.133, Rexp = 0.059, χ2 = 5.198 |
No. of data points | 15238 |
No. of parameters | 14 |
No. of restraints | ? |
H-atom treatment | H-atom parameters not refined |
Selected bond lengths (Å) topCs—Oi | 3.341 (3) | O—Oii | 2.505 (11) |
Cs—Oii | 3.410 (6) | O—O | 2.579 (6) |
Symmetry codes: (i) −x+1/2, y, −z+1/2; (ii) −y+1/4, −x+1/4, −z+3/4. |
Caesium hydroxide monohydrate, CsOH·H2O (or CsH3O2), is known to crystallize in three different hexagonal or pseudo-hexagonal modifications (Jacobs et al., 1982). Below 233 K the symmetry is monoclinic, between 233 and 340 K it is trigonal, and above 340 K the structure becomes truly hexagonal, at least so far as the positions of the Cs and O atoms are concerned (space group P6/mmm, a = 4.574 and c = 4.440 Å, Cs at 1a, O at 2 d). The O atoms form (001) layers with hexagonal symmetry, each O atom being connected to three neighbouring O atoms via hydrogen bonds. It has been shown by incoherent neutron scattering (Stahn et al., 1983) that at 402 K the H atoms are dynamically disordered in a double-well potential between adjacent O atoms, indicating that at this temperature it is impossible to distinguish between OH- ions and H2O molecules, and the structure can thus be rationalized in terms of (001) two-dimensional H3O2- ions separated by (001) layers of Cs+ ions.
The Rietveld refinement of the synchrotron data (Fig. 1.) measured on the present tetragonal polymorph shows that the same triangular coordination of O atoms as in the hexagonal polymorph can be found locally in the tetragonal phase, as bands running along the a axis at z ~1/4 and 3/4, and along the b axis at z ~0 and 1/2 (Fig. 2.). These bands form an infinite three-dimensional oxygen framework that is locally identical to the layers found in the hexagonal modification.
No H atoms were identified during the refinement, so the concept of bond valences (Brown & Wu, 1976) was used to locate the hydrogen bonds. The data of Brese & O'Keeffe (1991) were used to calculate the bond valences for all non-H atoms. The bond valences sum to 0.94 for Cs and to 0.47 for O, indicating that each O atom participates in three hydrogen bonds. Neutron diffraction on a deuterated sample would be necessary to localize the H atoms precisely and to determine whether, at room temperature, they are fully ordered (which would lead to a decrease of the symmetry), or disordered as in the hexagonal polymorph.
The Cs atoms are situated in the cavities of the oxygen framework, taking the form of a bicapped pentagonal prism. This form can be derived from a hexagonal prism (the Cs coordination observed in the hexagonal modification) by a 90° rotation of a half of the hexagonal prism.
The tetragonal polymorph of CsOH·H2O is a clathrate hydrate. The calculated density of the tetragonal modification of CsOH·H2O at ambient pressure and 293 K is 3.79 Mg m-3, which is higher than the density of the hexagonal polymorph, which was found to be 3.51 Mg m-3 at the same temperature and pressure.