Lithium and beryllium hypophosphites

The structures of monoclinic (C2/m) lithium di­hydrogenphosphate, LiH₂PO₂, and tetragonal (P4₁2₁2) beryllium bis(di­hydrogenphosphate), Be(H₂PO₂)₂, have been determined by single-crystal X-ray diffraction. The structures consist of layers of hypophosphite anions and metal cations in tetrahedral coordination by O atoms. Within the layers, the anions bridge four Li⁺ and two Be²⁺ cations, respectively. In LiH₂PO₂, the Li atom lies on a twofold axis and the H₂PO₂^- anion has the PO₂ atoms on a mirror plane. In Be(H₂PO₂)₂, the Be atom lies on a twofold axis and the H₂PO₂^- anion is in a general position.

S1. Comment

Previous studies of anhydrous hypophosphites include KH₂PO₂, RbH₂PO₂ and CsH₂PO₂ (Naumova Kuratieva Podberezskaya & Naumov, 2004), NH₄H₂PO₂ (Zachariasen & Mooney, 1934), Ca(H₂PO₂)₂ (Goedkoop & Loopstra, 1959), CaNa(H₂PO₂)₃ (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 compounds investigated is due to the difficulty of their preparation and crystal growth. This paper reports the results of our investigation of two further anhydrous hypophosphites, namely Li(H₂PO₂) and Be(H₂PO₂)₂. The hygroscopic nature of alkali and alkaline-earth hypophosphites makes the growth of their crystals generally difficult. Nevertheless, crystals of these Li and Be hypophosphites were obtained and their structures determined by X-ray diffraction. An initial report (Naumova Kuratieva Naumov & Podberezskaya, 2004) on the synthesis, growth conditions and crystal chemistry analysis of Li(H₂PO₂) was presented at the National Conference on Crystal Growth (NCCG-2002, Moscow).

Both title structures are layered and contain metal cations in tetrahedral coordination by O. The coordination environments of the Li⁺ and Be²⁺ cations are similar in both structures but, due to the different cation/anion ratios, the environments of the hypophosphite anions are different. The H₂PO₂⁻ anion has the shape of a slightly distorted tetrahedron, with the P atom at the centre and two O and two H atoms as vertices. It serves as a tetradentate and bidentate bridging ligand between the Li⁺ and Be²⁺ cations, respectively (Figs. 1 and 2). Separate layers are linked by van der Waals interactions (Figs. 3 and 4), with the shortest H···H distances between layers being 2.46 (5) and 2.70 (3) Å in Li(H₂PO₂) and Be(H₂PO₂)₂, respectively.

S2. Experimental

For small quantities, metal hypophosphites are usually synthesized from the corresponding sulfates and nitrates (Romanova & Demidenko, 1975), or carbonates (Naumova Kuratieva Podberezskaya & Naumov, 2004), hydroxides and oxides (Brun et al., 1972), by reaction with hypophosphorous acid, or Na and Ba hypophosphites. All these precursors have been tried in this work. Crystals of lithium hypophosphite were finally grown from an aqueous solution of lithium oxalate and calcium hypophosphite. Crystal growth was achieved by means of periodic cooling and heating cycles between 293 and 283 K Not a wide range?, every 12 h for 4 d in a speciallly constructed apparatus (Naumova Kuratieva Naumov & Podberezskaya, 2004). The precursors used for the preparation of lithium hypophosphite may play a role in the crystal growth. The crystals had a plate-like habit with a maximum dimension of 0.7 mm. Crystals of beryllium hypophosphite were grown in a small quantity at room temperature from an aqueous solution of hypophosphorous acid and beryllium carbonate. The latter was prepared from Be(NO₃)₂ (aqueous) and Na₂CO₃ (aqueous). Carbon dioxide was removed under vacuum. The crystals had a prismatic habit with a maximum dimension of 0.5 mm.

S3. Refinement

In both structures, the H atoms were located from difference electron-density maps. Their positions were refined without any constraint. The refinement of the Be(H₂PO₂)₂ structure was carried out on a twinned crystal, with refined volume fractions of 40 (4) and 60 (4)% for the two chiral twin components.

Computing details

For both 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.

Figures

	Fig. 1. The (001) layer in LiH2PO2. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The (001) layer in Be(H2PO2)2. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 3. A packing diagram for the LiH2PO2 structure, viewed along [010].
	Fig. 4. A packing diagram for the Be(H2PO2)2 structure, viewed along [100].

(I) lithium dihydrogenphosphate(I)

Crystal data

LiH2PO2	F(000) = 144
Mr = 71.93	Dx = 1.547 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 24 reflections
a = 9.3557 (11) Å	θ = 10.2–16.6°
b = 5.3107 (7) Å	µ = 0.62 mm^−1
c = 6.5432 (12) Å	T = 293 K
β = 108.259 (11)°	Plate, colourless
V = 308.73 (8) Å^3	0.47 × 0.43 × 0.09 mm
Z = 4

Data collection

Enraf-Nonius CAD-4 diffractometer	306 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.041
Graphite monochromator	θmax = 25.7°, θmin = 3.3°
2θ/θ scans	h = −11→10
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989)	k = −1→6
Tmin = 0.741, Tmax = 0.946	l = 0→7
430 measured reflections	3 standard reflections every 60 min
329 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	All H-atom parameters refined
wR(F^2) = 0.106	w = 1/[σ^2(Fo^2) + (0.0565P)^2 + 0.3682P] where P = (Fo^2 + 2Fc^2)/3
S = 1.15	(Δ/σ)max < 0.001
329 reflections	Δρmax = 0.38 e Å^−3
29 parameters	Δρmin = −0.24 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.16 (3)

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
Li	0.0000	0.2503 (10)	0.0000	0.0417 (12)
P	0.30832 (9)	0.5000	0.26808 (14)	0.0539 (5)
H	0.346 (4)	0.317 (7)	0.419 (5)	0.077 (10)*
O1	0.4156 (3)	0.5000	0.1435 (4)	0.0451 (7)
O2	0.1438 (2)	0.5000	0.1556 (4)	0.0446 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Li	0.028 (2)	0.036 (3)	0.066 (3)	0.000	0.021 (2)	0.000
P	0.0225 (6)	0.0985 (10)	0.0443 (7)	0.000	0.0156 (4)	0.000
O1	0.0332 (12)	0.0454 (14)	0.0678 (16)	0.000	0.0319 (11)	0.000
O2	0.0210 (11)	0.0464 (13)	0.0672 (15)	0.000	0.0148 (10)	0.000

Geometric parameters (Å, º)

Li—O1^i	1.933 (4)	P—O1	1.478 (2)
Li—O1^ii	1.933 (4)	P—O2	1.484 (2)
Li—O2	1.936 (4)	P—H	1.35 (4)
Li—O2^iii	1.936 (4)	O1—Li^i	1.933 (4)
Li—Li^iii	2.652 (11)	O1—Li^v	1.933 (4)
Li—Li^iv	2.658 (11)	O2—Li^iii	1.936 (4)
O1^i—Li—O1^ii	93.1 (2)	O1—P—H	109.7 (14)
O1^i—Li—O2	113.84 (9)	O2—P—H	110.7 (15)
O1^ii—Li—O2	122.55 (10)	P—O1—Li^i	135.99 (12)
O1^i—Li—O2^iii	122.55 (10)	P—O1—Li^v	135.99 (12)
O1^ii—Li—O2^iii	113.84 (9)	Li^i—O1—Li^v	86.9 (2)
O2—Li—O2^iii	93.5 (2)	P—O2—Li	134.67 (12)
O1—P—O2	120.30 (15)	P—O2—Li^iii	134.67 (12)
H^vi—P—H	92 (3)	Li—O2—Li^iii	86.5 (2)

Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x−1/2, y−1/2, z; (iii) −x, −y+1, −z; (iv) −x, −y, −z; (v) x+1/2, y+1/2, z; (vi) x, −y+1, z.

(II) beryllium bis[dihydrogenphosphate(I)]

Crystal data

Be(H2PO2)2	Dx = 1.833 Mg m^−3
Mr = 138.98	Mo Kα radiation, λ = 0.71073 Å
Tetragonal, P41212	Cell parameters from 22 reflections
Hall symbol: P 4abw 2nw	θ = 10.0–12.9°
a = 5.0117 (5) Å	µ = 0.76 mm^−1
c = 20.051 (3) Å	T = 293 K
V = 503.62 (10) Å^3	Prism, colourless
Z = 4	0.4 × 0.3 × 0.3 mm
F(000) = 280

Data collection

Enraf-Nonius CAD-4 diffractometer	599 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.032
Graphite monochromator	θmax = 29.9°, θmin = 4.1°
2θ/θ scans	h = −6→6
Absorption correction: empirical (using intensity measurements) (CADDAT; Enraf-Nonius, 1989)	k = −4→7
Tmin = 0.761, Tmax = 0.796	l = −27→28
1372 measured reflections	3 standard reflections every 60 min
699 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.033	w = 1/[σ^2(Fo^2) + (0.0592P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.098	(Δ/σ)max < 0.001
S = 1.08	Δρmax = 0.28 e Å^−3
699 reflections	Δρmin = −0.34 e Å^−3
43 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.018 (6)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983), with xx Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: 0.0 (4)

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
Be	0.0017 (6)	0.0017 (6)	0.0000	0.0326 (7)
P	0.49154 (11)	−0.07089 (14)	0.07203 (3)	0.0378 (2)
O1	0.2219 (3)	0.0397 (3)	0.05763 (8)	0.0426 (5)
O2	0.7104 (4)	0.0440 (4)	0.03120 (12)	0.0725 (8)
H1	0.554 (4)	−0.028 (4)	0.1381 (10)	0.029 (6)*
H2	0.495 (3)	−0.315 (5)	0.0620 (10)	0.040 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Be	0.0268 (10)	0.0268 (10)	0.0443 (19)	−0.0030 (15)	−0.0033 (11)	0.0033 (11)
P	0.0221 (3)	0.0480 (4)	0.0432 (4)	−0.0023 (2)	−0.0026 (2)	0.0100 (2)
O1	0.0241 (8)	0.0595 (12)	0.0442 (8)	0.0057 (7)	−0.0036 (6)	−0.0137 (8)
O2	0.0236 (8)	0.0925 (19)	0.1014 (17)	0.0017 (10)	0.0111 (10)	0.0487 (13)

Geometric parameters (Å, º)

Be—O1	1.609 (3)	P—O2	1.4848 (19)
Be—O1^i	1.609 (3)	P—H1	1.38 (2)
Be—O2^ii	1.603 (3)	P—H2	1.24 (3)
Be—O2^iii	1.603 (3)	O2—Be^iv	1.603 (3)
P—O1	1.4888 (16)
O1—Be—O1^i	110.7 (3)	H1—P—H2	108.0 (14)
O2^ii—Be—O1	107.29 (9)	O1—P—H2	110.3 (8)
O2^iii—Be—O1	109.20 (10)	O2—P—H2	106.5 (8)
O2^ii—Be—O1^i	109.20 (10)	O2—P—H1	107.6 (8)
O2^iii—Be—O1^i	107.29 (9)	O1—P—H1	109.5 (8)
O2^ii—Be—O2^iii	113.2 (3)	P—O2—Be^iv	146.79 (18)
O1—P—O2	114.78 (12)	P—O1—Be	135.86 (11)

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