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The structures of the hypophosphites KH2PO2 (potassium hypophosphite), RbH2PO2 (rubidium hypophosphite) and CsH2PO2 (caesium hypophosphite) have been determined by single-crystal X-ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.
Supporting information
It was established during crystal growth experiments that the preparation of anhydrous hypophosphites of K, Rb and Cs from aqueous solutions depends on the precursor and on the presence of impurities in that precursor at levels of less than 3–5%. Crystals of the title K, Rb, Cs hypophosphites were grown from aqueous solutions prepared by the reaction of hypophosphorous acid with the corresponding alkali carbonates. Crystal growth was carried out at 313 K in a dry box under dry nitrogen. Crystal growth is not possible at room temperature in air because of the strong hygroscopic nature of the hypophosphites and the tendency of the crystals to dissolve as a result of the fast absorption of water vapour from the atmosphere (increasing in the order K, Rb, Cs). The crystals were protected from moisture by coating them with epoxy resin. Powder diffraction analysis shows agreement between the bulk products and the single crystals. However, in the case of the rubidium hypophosphite, the presence of additional peaks in the powder pattern shows the presence of an additional phase similar to potassium hypophosphite.
The H atoms were located from difference electron-density maps and their positions were refined without any constraint.
For all compounds, data collection: CD4CA0 (Enraf-Nonius, 1989); cell refinement: CD4CA0; data reduction: CADDAT (Enraf-Nonius, 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97.
(I) Potassium hypophosphite
top
Crystal data top
KH2PO2 | F(000) = 208 |
Mr = 104.09 | Dx = 2.011 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2yc | Cell parameters from 22 reflections |
a = 7.3131 (10) Å | θ = 9.0–14.7° |
b = 7.2952 (8) Å | µ = 1.78 mm−1 |
c = 7.1814 (10) Å | T = 296 K |
β = 116.205 (10)° | Plate, colourless |
V = 343.75 (8) Å3 | 0.59 × 0.46 × 0.06 mm |
Z = 4 | |
Data collection top
Enraf-Nonius CAD4 diffractometer | 458 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.020 |
Graphite monochromator | θmax = 29.9°, θmin = 4.2° |
2θ/θ scans | h = 0→10 |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | k = −1→10 |
Tmin = 0.421, Tmax = 0.903 | l = −10→9 |
606 measured reflections | 3 standard reflections every 60 min |
500 independent reflections | intensity decay: none |
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)] = 0.031 | All H-atom parameters refined |
wR(F2) = 0.079 | w = 1/[σ2(Fo2) + (0.0549P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.14 | (Δ/σ)max < 0.001 |
500 reflections | Δρmax = 0.50 e Å−3 |
25 parameters | Δρmin = −0.59 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.075 (8) |
Crystal data top
KH2PO2 | V = 343.75 (8) Å3 |
Mr = 104.09 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 7.3131 (10) Å | µ = 1.78 mm−1 |
b = 7.2952 (8) Å | T = 296 K |
c = 7.1814 (10) Å | 0.59 × 0.46 × 0.06 mm |
β = 116.205 (10)° | |
Data collection top
Enraf-Nonius CAD4 diffractometer | 458 reflections with I > 2σ(I) |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | Rint = 0.020 |
Tmin = 0.421, Tmax = 0.903 | 3 standard reflections every 60 min |
606 measured reflections | intensity decay: none |
500 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.031 | 0 restraints |
wR(F2) = 0.079 | All H-atom parameters refined |
S = 1.14 | Δρmax = 0.50 e Å−3 |
500 reflections | Δρmin = −0.59 e Å−3 |
25 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(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 | x | y | z | Uiso*/Ueq | |
K | 0.5000 | 0.14284 (7) | 0.2500 | 0.0267 (2) | |
P | 0.0000 | 0.17744 (8) | 0.2500 | 0.0257 (2) | |
H | −0.119 (4) | 0.066 (3) | 0.112 (4) | 0.048 (7)* | |
O | 0.1173 (2) | 0.28267 (19) | 0.16055 (19) | 0.0337 (3) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
K | 0.0290 (3) | 0.0334 (3) | 0.0221 (3) | 0.000 | 0.0153 (2) | 0.000 |
P | 0.0310 (4) | 0.0282 (3) | 0.0240 (3) | 0.000 | 0.0178 (3) | 0.000 |
O | 0.0364 (7) | 0.0429 (7) | 0.0331 (6) | 0.0012 (5) | 0.0256 (6) | 0.0044 (5) |
Geometric parameters (Å, º) top
K—O | 2.7747 (14) | P—O | 1.4914 (12) |
K—Oi | 2.7368 (13) | P—Ovi | 1.4914 (12) |
K—Oii | 2.7368 (13) | P—H | 1.28 (3) |
K—Oiii | 2.7747 (14) | O—Ki | 2.7368 (13) |
K—Oiv | 2.9220 (15) | O—Kvii | 2.9220 (15) |
K—Ov | 2.9220 (15) | | |
| | | |
O—K—Oi | 82.73 (4) | O—K—Ov | 91.00 (2) |
O—K—Oii | 88.89 (3) | Oiv—K—Ov | 51.90 (5) |
O—K—Oiii | 136.86 (6) | O—P—Ovi | 118.04 (11) |
Oi—K—Oii | 157.10 (6) | O—P—H | 108.3 (10) |
Oi—K—Oiii | 88.89 (3) | Ovi—P—H | 109.8 (11) |
Oii—K—Oiii | 82.73 (4) | H—P—Hvi | 101 (2) |
Oi—K—Oiv | 85.67 (4) | P—O—Ki | 126.87 (7) |
Oii—K—Oiv | 115.63 (4) | P—O—K | 115.10 (7) |
Oiii—K—Oiv | 91.00 (2) | Ki—O—K | 97.27 (4) |
O—K—Oiv | 130.07 (5) | P—O—Kvii | 95.03 (6) |
Oi—K—Ov | 115.63 (4) | Ki—O—Kvii | 94.33 (4) |
Oii—K—Ov | 85.67 (4) | K—O—Kvii | 130.07 (5) |
Oiii—K—Ov | 130.07 (5) | | |
Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x+1/2, −y+1/2, z+1/2; (iii) −x+1, y, −z+1/2; (iv) x+1/2, y−1/2, z; (v) −x+1/2, y−1/2, −z+1/2; (vi) −x, y, −z+1/2; (vii) x−1/2, y+1/2, z. |
(II) Rubidium hypophosphite
top
Crystal data top
RbH2PO2 | F(000) = 280 |
Mr = 150.46 | Dx = 2.595 Mg m−3 |
Orthorhombic, Pnma | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2n | Cell parameters from 24 reflections |
a = 7.9835 (9) Å | θ = 9.9–14.2° |
b = 6.3678 (7) Å | µ = 13.06 mm−1 |
c = 7.5755 (11) Å | T = 298 K |
V = 385.12 (8) Å3 | Plate, colourless |
Z = 4 | 0.32 × 0.16 × 0.04 mm |
Data collection top
Enraf-Nonius CAD4 diffractometer | 289 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.032 |
Graphite monochromator | θmax = 24.9°, θmin = 3.7° |
2θ/θ scans | h = −9→9 |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | k = 0→7 |
Tmin = 0.095, Tmax = 0.593 | l = 0→9 |
732 measured reflections | 3 standard reflections every 60 min |
366 independent reflections | intensity decay: none |
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)] = 0.023 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.057 | All H-atom parameters refined |
S = 0.96 | w = 1/[σ2(Fo2) + (0.026P)2] where P = (Fo2 + 2Fc2)/3 |
366 reflections | (Δ/σ)max < 0.001 |
27 parameters | Δρmax = 0.58 e Å−3 |
0 restraints | Δρmin = −0.58 e Å−3 |
Crystal data top
RbH2PO2 | V = 385.12 (8) Å3 |
Mr = 150.46 | Z = 4 |
Orthorhombic, Pnma | Mo Kα radiation |
a = 7.9835 (9) Å | µ = 13.06 mm−1 |
b = 6.3678 (7) Å | T = 298 K |
c = 7.5755 (11) Å | 0.32 × 0.16 × 0.04 mm |
Data collection top
Enraf-Nonius CAD4 diffractometer | 289 reflections with I > 2σ(I) |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | Rint = 0.032 |
Tmin = 0.095, Tmax = 0.593 | 3 standard reflections every 60 min |
732 measured reflections | intensity decay: none |
366 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.023 | 0 restraints |
wR(F2) = 0.057 | All H-atom parameters refined |
S = 0.96 | Δρmax = 0.58 e Å−3 |
366 reflections | Δρmin = −0.58 e Å−3 |
27 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(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 | x | y | z | Uiso*/Ueq | |
Rb | 0.63134 (9) | 0.2500 | 0.13795 (8) | 0.0322 (3) | |
P | 0.3847 (3) | 0.7500 | 0.3289 (2) | 0.0343 (4) | |
H1 | 0.491 (10) | 0.7500 | 0.437 (8) | 0.041* | |
H2 | 0.255 (9) | 0.7500 | 0.439 (9) | 0.041* | |
O | 0.3797 (5) | 0.5504 (4) | 0.2297 (4) | 0.0434 (8) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Rb | 0.0286 (4) | 0.0313 (4) | 0.0368 (4) | 0.000 | −0.0015 (4) | 0.000 |
P | 0.0356 (10) | 0.0335 (8) | 0.0336 (9) | 0.000 | 0.0024 (10) | 0.000 |
O | 0.0471 (19) | 0.0297 (15) | 0.0533 (19) | 0.000 (2) | 0.0100 (19) | −0.0003 (15) |
Geometric parameters (Å, º) top
Rb—O | 2.859 (3) | P—O | 1.478 (3) |
Rb—Oi | 2.932 (3) | P—Ovi | 1.478 (3) |
Rb—Oii | 2.859 (3) | P—H1 | 1.18 (7) |
Rb—Oiii | 2.932 (3) | P—H2 | 1.33 (7) |
Rb—Oiv | 3.063 (3) | O—Rbvii | 2.932 (3) |
Rb—Ov | 3.063 (3) | O—Rbv | 3.063 (3) |
| | | |
O—Rb—Oii | 83.96 (13) | Oiv—Rb—Ov | 49.05 (10) |
O—Rb—Oiii | 87.46 (7) | O—P—Ovi | 118.7 (3) |
O—Rb—Oi | 145.93 (3) | O—P—H1 | 111.9 (13) |
Oii—Rb—Oiii | 145.93 (3) | Ovi—P—H1 | 111.9 (13) |
Oii—Rb—Oi | 87.46 (7) | O—P—H2 | 107.4 (13) |
Oiii—Rb—Oi | 81.44 (12) | Ovi—P—H2 | 107.4 (13) |
Oii—Rb—Oiv | 85.58 (9) | H1—P—H2 | 97 (4) |
O—Rb—Oiv | 118.58 (6) | P—O—Rb | 132.9 (2) |
Oiii—Rb—Oiv | 126.97 (7) | P—O—Rbvii | 113.91 (18) |
Oi—Rb—Oiv | 93.43 (6) | Rb—O—Rbvii | 97.00 (8) |
Oii—Rb—Ov | 118.58 (6) | P—O—Rbv | 96.11 (13) |
O—Rb—Ov | 85.58 (9) | Rb—O—Rbv | 94.42 (9) |
Oiii—Rb—Ov | 93.43 (6) | Rbvii—O—Rbv | 124.22 (12) |
Oi—Rb—Ov | 126.97 (7) | | |
Symmetry codes: (i) x+1/2, −y+1/2, −z+1/2; (ii) x, −y+1/2, z; (iii) x+1/2, y, −z+1/2; (iv) −x+1, y−1/2, −z; (v) −x+1, −y+1, −z; (vi) x, −y+3/2, z; (vii) x−1/2, y, −z+1/2. |
(III) Caesium hypophosphite
top
Crystal data top
CsH2PO2 | F(000) = 352 |
Mr = 197.90 | Dx = 2.991 Mg m−3 |
Orthorhombic, Pnma | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ac 2n | Cell parameters from 24 reflections |
a = 8.3776 (9) Å | θ = 9.5–13.7° |
b = 6.6271 (6) Å | µ = 8.61 mm−1 |
c = 7.9165 (10) Å | T = 298 K |
V = 439.52 (8) Å3 | Plate, colourless |
Z = 4 | 0.45 × 0.30 × 0.11 mm |
Data collection top
Enraf-Nonius CAD4 diffractometer | 554 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.058 |
Graphite monochromator | θmax = 29.9°, θmin = 3.5° |
2θ/θ scans | h = −1→11 |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | k = 0→9 |
Tmin = 0.056, Tmax = 0.388 | l = 0→11 |
769 measured reflections | 3 standard reflections every 60 min |
687 independent reflections | intensity decay: none |
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)] = 0.037 | All H-atom parameters refined |
wR(F2) = 0.114 | w = 1/[σ2(Fo2) + (0.07P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.04 | (Δ/σ)max < 0.001 |
687 reflections | Δρmax = 1.41 e Å−3 |
27 parameters | Δρmin = −1.06 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.050 (4) |
Crystal data top
CsH2PO2 | V = 439.52 (8) Å3 |
Mr = 197.90 | Z = 4 |
Orthorhombic, Pnma | Mo Kα radiation |
a = 8.3776 (9) Å | µ = 8.61 mm−1 |
b = 6.6271 (6) Å | T = 298 K |
c = 7.9165 (10) Å | 0.45 × 0.30 × 0.11 mm |
Data collection top
Enraf-Nonius CAD4 diffractometer | 554 reflections with I > 2σ(I) |
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | Rint = 0.058 |
Tmin = 0.056, Tmax = 0.388 | 3 standard reflections every 60 min |
769 measured reflections | intensity decay: none |
687 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.037 | 0 restraints |
wR(F2) = 0.114 | All H-atom parameters refined |
S = 1.04 | Δρmax = 1.41 e Å−3 |
687 reflections | Δρmin = −1.06 e Å−3 |
27 parameters | |
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(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 | x | y | z | Uiso*/Ueq | |
Cs | 0.63434 (6) | 0.2500 | 0.13628 (8) | 0.0404 (3) | |
P | 0.3901 (3) | 0.7500 | 0.3333 (4) | 0.0461 (6) | |
H1 | 0.528 (13) | 0.7500 | 0.425 (15) | 0.055* | |
H2 | 0.255 (13) | 0.7500 | 0.453 (16) | 0.055* | |
O | 0.3849 (5) | 0.5577 (9) | 0.2368 (9) | 0.0584 (15) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cs | 0.0410 (4) | 0.0360 (4) | 0.0443 (4) | 0.000 | −0.0005 (2) | 0.000 |
P | 0.0511 (14) | 0.0427 (14) | 0.0445 (14) | 0.000 | 0.0017 (11) | 0.000 |
O | 0.065 (3) | 0.036 (3) | 0.074 (4) | 0.003 (2) | 0.012 (3) | 0.000 (3) |
Geometric parameters (Å, º) top
Cs—Oi | 3.026 (5) | P—O | 1.487 (6) |
Cs—O | 3.026 (5) | P—Ovi | 1.487 (6) |
Cs—Oii | 3.094 (5) | P—H1 | 1.37 (11) |
Cs—Oiii | 3.094 (5) | P—H2 | 1.48 (12) |
Cs—Oiv | 3.221 (7) | O—Csvii | 3.094 (5) |
Cs—Ov | 3.221 (7) | O—Csv | 3.221 (7) |
| | | |
O—Cs—Oi | 84.7 (2) | Oiv—Cs—Ov | 46.6 (2) |
O—Cs—Oii | 86.51 (14) | O—P—Ovi | 118.1 (5) |
O—Cs—Oiii | 145.80 (5) | O—P—H1 | 107 (2) |
Oi—Cs—Oii | 145.80 (5) | Ovi—P—H1 | 107 (2) |
Oi—Cs—Oiii | 86.51 (14) | O—P—H2 | 108 (2) |
Oii—Cs—Oiii | 82.45 (19) | Ovi—P—H2 | 108 (2) |
Oi—Cs—Oiv | 86.57 (17) | H1—P—H2 | 108 (7) |
O—Cs—Oiv | 118.25 (11) | P—O—Cs | 133.8 (3) |
Oii—Cs—Oiv | 126.33 (16) | P—O—Csvii | 114.7 (3) |
Oiii—Cs—Oiv | 94.06 (9) | Cs—O—Csvii | 96.31 (16) |
Oi—Cs—Ov | 118.25 (11) | P—O—Csv | 97.7 (3) |
O—Cs—Ov | 86.57 (17) | Cs—O—Csv | 93.43 (17) |
Oii—Cs—Ov | 94.06 (9) | Csvii—O—Csv | 121.64 (18) |
Oiii—Cs—Ov | 126.33 (16) | | |
Symmetry codes: (i) x, −y+1/2, z; (ii) x+1/2, y, −z+1/2; (iii) x+1/2, −y+1/2, −z+1/2; (iv) −x+1, y−1/2, −z; (v) −x+1, −y+1, −z; (vi) x, −y+3/2, z; (vii) x−1/2, y, −z+1/2. |
Experimental details
| (I) | (II) | (III) |
Crystal data |
Chemical formula | KH2PO2 | RbH2PO2 | CsH2PO2 |
Mr | 104.09 | 150.46 | 197.90 |
Crystal system, space group | Monoclinic, C2/c | Orthorhombic, Pnma | Orthorhombic, Pnma |
Temperature (K) | 296 | 298 | 298 |
a, b, c (Å) | 7.3131 (10), 7.2952 (8), 7.1814 (10) | 7.9835 (9), 6.3678 (7), 7.5755 (11) | 8.3776 (9), 6.6271 (6), 7.9165 (10) |
α, β, γ (°) | 90, 116.205 (10), 90 | 90, 90, 90 | 90, 90, 90 |
V (Å3) | 343.75 (8) | 385.12 (8) | 439.52 (8) |
Z | 4 | 4 | 4 |
Radiation type | Mo Kα | Mo Kα | Mo Kα |
µ (mm−1) | 1.78 | 13.06 | 8.61 |
Crystal size (mm) | 0.59 × 0.46 × 0.06 | 0.32 × 0.16 × 0.04 | 0.45 × 0.30 × 0.11 |
|
Data collection |
Diffractometer | Enraf-Nonius CAD4 diffractometer | Enraf-Nonius CAD4 diffractometer | Enraf-Nonius CAD4 diffractometer |
Absorption correction | Empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | Empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) | Empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989) |
Tmin, Tmax | 0.421, 0.903 | 0.095, 0.593 | 0.056, 0.388 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 606, 500, 458 | 732, 366, 289 | 769, 687, 554 |
Rint | 0.020 | 0.032 | 0.058 |
(sin θ/λ)max (Å−1) | 0.702 | 0.592 | 0.702 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.031, 0.079, 1.14 | 0.023, 0.057, 0.96 | 0.037, 0.114, 1.04 |
No. of reflections | 500 | 366 | 687 |
No. of parameters | 25 | 27 | 27 |
H-atom treatment | All H-atom parameters refined | All H-atom parameters refined | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.50, −0.59 | 0.58, −0.58 | 1.41, −1.06 |
Selected geometric parameters (Å, º) for (I) topK—O | 2.7747 (14) | P—O | 1.4914 (12) |
K—Oi | 2.7368 (13) | P—H | 1.28 (3) |
K—Oii | 2.9220 (15) | | |
| | | |
O—P—Oiii | 118.04 (11) | Oiii—P—H | 109.8 (11) |
O—P—H | 108.3 (10) | H—P—Hiii | 101 (2) |
Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x+1/2, y−1/2, z; (iii) −x, y, −z+1/2. |
Selected geometric parameters (Å, º) for (II) topRb—O | 2.859 (3) | P—O | 1.478 (3) |
Rb—Oi | 2.932 (3) | P—H1 | 1.18 (7) |
Rb—Oii | 3.063 (3) | P—H2 | 1.33 (7) |
| | | |
O—P—Oiii | 118.7 (3) | O—P—H2 | 107.4 (13) |
O—P—H1 | 111.9 (13) | H1—P—H2 | 97 (4) |
Symmetry codes: (i) x+1/2, −y+1/2, −z+1/2; (ii) −x+1, y−1/2, −z; (iii) x, −y+3/2, z. |
Selected geometric parameters (Å, º) for (III) topCs—O | 3.026 (5) | P—O | 1.487 (6) |
Cs—Oi | 3.094 (5) | P—H1 | 1.37 (11) |
Cs—Oii | 3.221 (7) | P—H2 | 1.48 (12) |
| | | |
O—P—Oiii | 118.1 (5) | O—P—H2 | 108 (2) |
O—P—H1 | 107 (2) | H1—P—H2 | 108 (7) |
Symmetry codes: (i) x+1/2, −y+1/2, −z+1/2; (ii) −x+1, y−1/2, −z; (iii) x, −y+3/2, z. |
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The hypophosphite H2PO22− anion is a distorted tetrahedron, with the P atom at the centre and two O and two H atoms at the vertices. This anion may coordinate a metal cation via the O atoms in different ways, viz. as a mono- or bidentate ligand, or as a bridging ligand between two cations. The goal of the present work was to investigate further the functional role of the hypophosphite anion in the crystals of the title compounds.
Previous crystal-structure investigations of anhydrous hypophosphites include Ca(H2PO2)2 (Goedkoop & Loopstra, 1959), CaNa(H2PO2)2 (Matsuzaki & Iitaka, 1969), Cu(H2PO2)2 (Naumov et al., 2002), Zn(H2PO2)2 (Weakley, 1979; Tanner et al., 1997), GeCl(H2PO2) and SnCl(H2PO2) (Weakley & Watt, 1979), La(H2PO2)3 (Tanner et al., 1999), Er(H2PO2)3 (Aslanov et al., 1975), and U(H2PO2)4 (Tanner et al., 1992). The limited number of studies is probably due to the difficulty of preparation of these compounds, resulting from their highly hygroscopic nature and their low stability. The title compounds are rather easy to synthesize but crystals are difficult to grow.
The present crystal-structure determinations show that the unit-cell of KH2PO2 differs in size and symmetry from those of the isostructural Rb and Cs analogues. The monoclinic unit cell of KH2PO2 is related to the orthorhombic unit cell of the Rb and Cs hypophosphites by the matrix (1/2 − 1 0 / 1/2 1 0 / 0 0 1).
All three compounds adopt layer structures, in which the metal cations are coordinated by hypophosphite anions (Figs. 1 and 2). The packing of the cations and P atoms is identical in all three compounds, and the cations and P positions are nearly coplanar, forming a layer similar to a (100) NaCl layer.
The full coordination environments of the K+ and Rb+ cations are shown in Figs. 3 and 4, respectively. The Rb and Cs environments are identical to those found in KF2PO2, RbF2PO2 and CsF2PO2 (Harrison et al., 1966; Granier et al., 1975; Trotter & Withlow, 1967). The H-atom positions in the present hypophosphites correspond to the F positions in the difluorophosphates.