Layered calcium hydrogenphosphite monohydrate at 173 K

The crystal structure of the title compound, Ca(H₂PO₃)₂·H₂O, exhibits two-dimensional sheets formed by linked Ca and P polyhedra. The layers are held together by O—H...O hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• R factor = 0.027
• wR factor = 0.074
• Data-to-parameter ratio = 20.8

checkCIF results

No syntax errors found



ADDSYM reports no extra symmetry


 Alert Level C:



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           32.82
         From the CIF: _reflns_number_total               2416
         TEST2: Reflns within _diffrn_reflns_theta_max
         Count of symmetry unique reflns         2648
         Completeness (_total/calc)             91.24%
          Alert C: < 95% complete


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

Metal phosphites, phosphates and phosphonates are a rich class of compounds which are of current interest in many areas from fundamental research to industrial applications and medicine. The general interest in the chemistry of these compounds is mainly due to their wide range of chemical composition and structural diversity. Those with a layered structure are more important to perform chemistry such as intercalation, ion exchange and catalysis, or to function as proton conductors, chemical sensors, etc (Clearfield, 1998; Alberti, 1996; Mallouk et al., 1996). We are interested in the chemical characteristics of phosphites and phosphonates of alkaline-earth metals, including calcium, to obtain chemically modified surfaces and thin films for the protection of different objects such as stones and metals againts atmospheric influences, corrosion and decay. The study of structure-property relationships of both calcium phosphites and phosphonates, would lead us to design new materials with required properties.

In general, divalent metal phosphites and phosphonates are rather soluble, especially at low pH values, which is to some extent an advantage, since one can obtain them at relatively mild conditions, or to grow single crystals for diffraction studies. There are several reports on the structure of alkaline-earth metal phosphates, but there are only few structures for phosphites (Corbridge, 1956; Larbot et al., 1984; Powell et al., 1994). The crystal structure of calcium hydrogenphosphite monohydrate, Ca(H₂PO₃)₂^.H₂O has been repoted by Larbot et al. (1984). Their choice of unit cell is different that that ours. According to the rules and definitions from the International Tables of Crystallography (Vol. A, 1983, pp. 734–740), we have choosen a reduced cell, which for Larbot et al. data will be a = 6.773 (1), b = 7.007 (1), c = 8.100 (1) Å, α = 68.00 (1), β = 84.92 (1), γ = 84.28 (1)°. Compared to our data, their unit-cell volume is smaller for room temperature [354.10 (9) ų]. Larbot et al. based their cell parameters on 20 reflections in θ range 1–25°, while our data are based on 4179 with I>10σ(I) reflections in θ range 1–32.82°. Therefore, we would rather compare parameters obtained from same crystal, same diffractometer and setup. Our cell parameters for room temperature are a = 6.7857 (1), b = 7.0229 (1), c = 8.1154 (1) Å, α = 68.035 (1), β = 84.997 (1), γ = 84.363 (1)° and V = 356.401 (9) ų. Our data are of a better precision of the factor of ten and show the expected temperature dependence.

Furthermore, there is no discusion about the packing features by Larbot et al. and, indeed, their discusion about interaction of (P—)H with O atoms in the form of hydrogen bonding is misleading and there are no hydrogen bonds of this type in the structure. Here we present structure redetermination at 173 K using data from a Siemens SMART CCD diffractometer. The compound Ca(H₂PO₃)₂^.H₂O, crystallizes in triclinic system with space group P1 (No. 2). As shown in Fig. 1, the calcium ion is coordinated by seven O atoms with the Ca—O bond distances ranging from 2.3531 (10) to 2.5307 (11) Å. One of the phosphite groups is chelated to the calcium ion through O11 and O13, while the other one is just linked through O21 to the central atom. Each Ca atom is then connected to the second calcium atom by a bridging O13 atom, symmetry related by (1 - x, -y, 1 - z), to form a binuclear calcium phosphite (see Fig. 2). Each building block of this type is linked to other units through bridging O atoms of phosphite groups forming two-dimensional sheets aligned parallel to the ab plane. The water molecules are coordinated at axial positions of binuclear units to the Ca atoms, sticking out the layers. Between the layers, water molecules are involved in hydrogen bonding with O atoms of the phosphite groups from next layers. Within the layers, the O12 atom is involved in hydrogen bonding with the H22 atom, stabilizing the two-dimensional inorganic framework. The layered structure is represented by Figs. 3(a) (top view) and 3(b) (side view). Based on this study, we can describe the solubility of calcium hydrogenphosphite monohydrate to be related to the presence of high water accessible area within the layers.

S2. Experimental

Crystals suitable for X-ray diffraction analysis were obtained by very slow evaporation of the saturated solution of calcium hydrogenphosphite monohydrate in water after few days.

S3. Refinement

Data were collected using a Siemens SMART CCD diffractometer equipped with a Siemens LT-2 A low-temperature device at 173 K. A full sphere of reciprocal space was scanned by 0.3° steps in ω with a crystal-to-detector distance of 3.97 cm. Preliminary orientation matrix was obtained from the first 100 frames using SMART (Siemens, 1995). The collected frames were integrated using the preliminary orientation matrix which was updated every 100 frames·Final cell parameters were obtained by refinement on the position of 4179 reflections with I > 10σ(I) after integration of all the frames data using SAINT (Siemens, 1995). The data were empirically corrected for absorption and other effects using SADABS (Sheldrick, 1996) based on the method of Blessing (1995). The structure was solved by Patterson method and refined by full-matrix least squares on all F² data using SHELXTL (Bruker, 1997). The non-H atoms were refined anisotropically. The H atoms were located from difference Fourier maps and refined isotropically.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT and SADABS (Sheldrick, 1996); program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The geometry around calcium ion in the crystal structure of Ca(H2PO3)2^.H2O with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level. Symmetry codes are given in Table 1.
	Fig. 2. The geometry of a binuclear unit as a building block of the layered structure with atom-numbering scheme for the asymmetric unit. Displacement ellipsoids are shown at the 50% probability level. Symmetry codes are given in Table 1.
	Fig. 3. Two-dimensional layer of calcium hydrogenphosphite monohydrate parallel to ab plane. (a) Top view showing the binuclear units linking togther by the P polyhera. (b) Side view showing the water molecules sticking out the layer.

(CAHPM)

Crystal data

Ca(H2PO3)2·H2O	Z = 2
Mr = 220.07	F(000) = 224
Triclinic, P1	Dx = 2.059 Mg m^−3
a = 6.7777 (2) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.0282 (1) Å	Cell parameters from 4179 reflections
c = 8.0970 (2) Å	θ = 1–32°
α = 67.906 (1)°	µ = 1.32 mm^−1
β = 84.812 (1)°	T = 173 K
γ = 84.236 (1)°	Parallelipide, colorless
V = 354.99 (2) Å^3	0.65 × 0.55 × 0.35 mm

Data collection

Siemens SMART CCD diffractometer	2416 independent reflections
Radiation source: fine-focus sealed tube	2254 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
w scans	θmax = 32.8°, θmin = 2.7°
Absorption correction: multi-scan (Blessing, 1995)	h = −10→9
Tmin = 0.481, Tmax = 0.655	k = −10→10
5023 measured reflections	l = −12→12

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.027	All H-atom parameters refined
wR(F^2) = 0.074	w = 1/[σ^2(Fo^2) + (0.0396P)^2 + 0.290P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.001
2416 reflections	Δρmax = 0.47 e Å^−3
116 parameters	Δρmin = −0.59 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: patterson	Extinction coefficient: 0.123 (7)

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Ca	0.64084 (4)	0.13039 (4)	0.26545 (3)	0.00791 (8)
P1	0.18703 (5)	0.03862 (5)	0.28239 (5)	0.00830 (9)
P2	0.74489 (5)	0.59192 (5)	0.31997 (5)	0.00905 (9)
O7	0.69560 (18)	0.3184 (2)	−0.04596 (15)	0.0169 (2)
O11	0.33483 (16)	0.11869 (18)	0.11305 (14)	0.0138 (2)
O12	−0.01027 (15)	0.16313 (17)	0.25713 (15)	0.0130 (2)
O13	0.31007 (15)	0.03994 (17)	0.42806 (14)	0.0129 (2)
O21	0.60355 (15)	0.45708 (16)	0.28996 (15)	0.0129 (2)
O22	0.96621 (16)	0.52289 (18)	0.27500 (18)	0.0176 (2)
O23	0.71334 (16)	0.82143 (16)	0.21515 (14)	0.01235 (19)
H1	0.155 (4)	−0.142 (4)	0.308 (3)	0.017 (5)*
H2	0.738 (3)	0.565 (3)	0.483 (3)	0.016 (5)*
H11	0.308 (5)	0.127 (5)	0.009 (4)	0.043 (8)*
H22	0.972 (5)	0.393 (6)	0.264 (5)	0.053 (9)*
H71	0.602 (5)	0.384 (5)	−0.114 (5)	0.044 (8)*
H72	0.805 (5)	0.349 (5)	−0.100 (4)	0.035 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ca	0.00700 (12)	0.00853 (13)	0.00879 (13)	−0.00062 (8)	−0.00029 (8)	−0.00390 (9)
P1	0.00641 (15)	0.00931 (16)	0.00941 (16)	−0.00048 (11)	−0.00051 (11)	−0.00376 (12)
P2	0.00941 (16)	0.00831 (15)	0.00984 (16)	−0.00042 (11)	−0.00099 (11)	−0.00378 (12)
O7	0.0115 (5)	0.0229 (5)	0.0122 (5)	−0.0039 (4)	−0.0002 (4)	−0.0014 (4)
O11	0.0101 (4)	0.0228 (5)	0.0091 (4)	−0.0023 (4)	0.0002 (3)	−0.0066 (4)
O12	0.0074 (4)	0.0134 (5)	0.0187 (5)	0.0005 (3)	−0.0019 (3)	−0.0064 (4)
O13	0.0100 (4)	0.0196 (5)	0.0092 (4)	−0.0028 (4)	−0.0011 (3)	−0.0048 (4)
O21	0.0107 (4)	0.0108 (4)	0.0188 (5)	−0.0004 (3)	−0.0011 (4)	−0.0075 (4)
O22	0.0090 (4)	0.0137 (5)	0.0312 (6)	−0.0012 (4)	0.0015 (4)	−0.0103 (4)
O23	0.0171 (5)	0.0076 (4)	0.0130 (4)	0.0003 (3)	−0.0019 (4)	−0.0047 (3)

Geometric parameters (Å, º)

Ca—O23^i	2.3531 (10)	P1—H1	1.24 (2)
Ca—O13^ii	2.3531 (11)	P2—O21	1.5075 (11)
Ca—O21	2.3648 (11)	P2—O23	1.5172 (11)
Ca—O7	2.3800 (12)	P2—O22	1.5831 (12)
Ca—O12^iii	2.3912 (11)	P2—H2	1.26 (2)
Ca—O13	2.5073 (11)	O7—H71	0.86 (4)
Ca—O11	2.5307 (11)	O7—H72	0.83 (3)
Ca—P1	3.1861 (4)	O11—H11	0.86 (3)
Ca—Ca^ii	3.9479 (5)	O12—Ca^iv	2.3912 (11)
P1—O13	1.5081 (11)	O13—Ca^ii	2.3530 (11)
P1—O12	1.5085 (11)	O22—H22	0.95 (3)
P1—O11	1.5763 (11)	O23—Ca^v	2.3531 (10)
O23^i—Ca—O13^ii	91.29 (4)	O13—Ca—Ca^ii	34.40 (2)
O23^i—Ca—O21	172.57 (4)	O11—Ca—Ca^ii	89.69 (3)
O13^ii—Ca—O21	92.37 (4)	P1—Ca—Ca^ii	60.630 (9)
O23^i—Ca—O7	89.43 (4)	O13—P1—O12	117.39 (6)
O13^ii—Ca—O7	162.46 (4)	O13—P1—O11	101.66 (6)
O21—Ca—O7	85.14 (4)	O12—P1—O11	112.28 (6)
O23^i—Ca—O12^iii	88.83 (4)	O13—P1—Ca	50.30 (4)
O13^ii—Ca—O12^iii	81.40 (4)	O12—P1—Ca	136.25 (4)
O21—Ca—O12^iii	85.34 (4)	O11—P1—Ca	51.66 (4)
O7—Ca—O12^iii	81.10 (4)	O13—P1—H1	109.2 (11)
O23^i—Ca—O13	96.20 (4)	O12—P1—H1	107.7 (11)
O13^ii—Ca—O13	71.41 (4)	O11—P1—H1	108.2 (11)
O21—Ca—O13	91.09 (4)	Ca—P1—H1	116.0 (11)
O7—Ca—O13	125.92 (4)	O21—P2—O23	116.46 (6)
O12^iii—Ca—O13	152.41 (4)	O21—P2—O22	109.89 (6)
O23^i—Ca—O11	78.84 (4)	O23—P2—O22	107.32 (6)
O13^ii—Ca—O11	125.18 (4)	O21—P2—H2	109.8 (10)
O21—Ca—O11	104.18 (4)	O23—P2—H2	107.8 (10)
O7—Ca—O11	72.10 (4)	O22—P2—H2	104.9 (10)
O12^iii—Ca—O11	150.44 (4)	Ca—O7—H71	123 (2)
O13—Ca—O11	56.68 (3)	Ca—O7—H72	126 (2)
O23^i—Ca—P1	85.57 (3)	H71—O7—H72	110 (3)
O13^ii—Ca—P1	96.99 (3)	P1—O11—Ca	99.10 (5)
O21—Ca—P1	100.38 (3)	P1—O11—H11	123 (2)
O7—Ca—P1	100.53 (3)	Ca—O11—H11	137 (2)
O12^iii—Ca—P1	174.15 (3)	P1—O12—Ca^iv	142.08 (6)
O13—Ca—P1	27.57 (2)	P1—O13—Ca^ii	141.93 (6)
O11—Ca—P1	29.24 (3)	P1—O13—Ca	102.14 (5)
O23^i—Ca—Ca^ii	94.70 (3)	Ca^ii—O13—Ca	108.59 (4)
O13^ii—Ca—Ca^ii	37.01 (3)	P2—O21—Ca	133.88 (6)
O21—Ca—Ca^ii	92.11 (3)	P2—O22—H22	110 (2)
O7—Ca—Ca^ii	160.20 (3)	P2—O23—Ca^v	139.62 (6)
O12^iii—Ca—Ca^ii	118.28 (3)

Symmetry codes: (i) x, y−1, z; (ii) −x+1, −y, −z+1; (iii) x+1, y, z; (iv) x−1, y, z; (v) x, y+1, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O7—H72···O22^vi	0.83 (3)	2.03 (3)	2.8506 (16)	167 (3)
O11—H11···O23^vii	0.86 (3)	1.73 (3)	2.5756 (15)	169 (3)
O7—H71···O21^vii	0.86 (4)	2.02 (4)	2.8707 (16)	176 (3)
O22—H22···O12^iii	0.95 (3)	1.63 (4)	2.5748 (16)	176 (4)

Symmetry codes: (iii) x+1, y, z; (vi) −x+2, −y+1, −z; (vii) −x+1, −y+1, −z.