The structures of monoclinic (C2/m) lithium dihydrogenphosphate, LiH_{2}PO_{2}, and tetragonal (P4_{1}2_{1}2) beryllium bis(dihydrogenphosphate), Be(H_{2}PO_{2})_{2}, have been determined by singlecrystal Xray 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 Be^{2+} cations, respectively. In LiH_{2}PO_{2}, the Li atom lies on a twofold axis and the H_{2}PO_{2}^{} anion has the PO_{2} atoms on a mirror plane. In Be(H_{2}PO_{2})_{2}, the Be atom lies on a twofold axis and the H_{2}PO_{2}^{} anion is in a general position.
Supporting information
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 platelike 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(NO_{3})_{2} (aqueous) and Na_{2}CO_{3} (aqueous). Carbon dioxide was removed under vacuum. The crystals had a prismatic habit with a maximum dimension of 0.5 mm.
In both structures, the H atoms were located from difference electrondensity maps. Their positions were refined without any constraint. The refinement of the Be(H_{2}PO_{2})_{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.
For both compounds, data collection: CD4CA0 (EnrafNonius, 1989); cell refinement: CD4CA0; data reduction: CADDAT (EnrafNonius, 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) lithium dihydrogenphosphate(I)
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Crystal data top
LiH_{2}PO_{2}  F(000) = 144 
M_{r} = 71.93  D_{x} = 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 top
EnrafNonius CAD4 diffractometer  306 reflections with I > 2σ(I) 
Radiation source: finefocus sealed tube  R_{int} = 0.041 
Graphite monochromator  θ_{max} = 25.7°, θ_{min} = 3.3° 
2θ/θ scans  h = −11→10 
Absorption correction: empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989)  k = −1→6 
T_{min} = 0.741, T_{max} = 0.946  l = 0→7 
430 measured reflections  3 standard reflections every 60 min 
329 independent reflections  intensity decay: none 
Refinement top
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  Hydrogen site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.038  All Hatom parameters refined 
wR(F^{2}) = 0.106  w = 1/[σ^{2}(F_{o}^{2}) + (0.0565P)^{2} + 0.3682P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
S = 1.15  (Δ/σ)_{max} < 0.001 
329 reflections  Δρ_{max} = 0.38 e Å^{−}^{3} 
29 parameters  Δρ_{min} = −0.24 e Å^{−}^{3} 
0 restraints  Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
Primary atom site location: structureinvariant direct methods  Extinction coefficient: 0.16 (3) 
Crystal data top
LiH_{2}PO_{2}  V = 308.73 (8) Å^{3} 
M_{r} = 71.93  Z = 4 
Monoclinic, C2/m  Mo Kα radiation 
a = 9.3557 (11) Å  µ = 0.62 mm^{−}^{1} 
b = 5.3107 (7) Å  T = 293 K 
c = 6.5432 (12) Å  0.47 × 0.43 × 0.09 mm 
β = 108.259 (11)°  
Data collection top
EnrafNonius CAD4 diffractometer  306 reflections with I > 2σ(I) 
Absorption correction: empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989)  R_{int} = 0.041 
T_{min} = 0.741, T_{max} = 0.946  3 standard reflections every 60 min 
430 measured reflections  intensity decay: none 
329 independent reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.038  0 restraints 
wR(F^{2}) = 0.106  All Hatom parameters refined 
S = 1.15  Δρ_{max} = 0.38 e Å^{−}^{3} 
329 reflections  Δρ_{min} = −0.24 e Å^{−}^{3} 
29 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 F^{2} against ALL reflections. The weighted Rfactor wR and goodness of fit S are based on F^{2}, conventional Rfactors R are based on F, with F set to zero for negative F^{2}. The threshold expression of F^{2} > σ(F^{2}) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. Rfactors based on F^{2} 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 (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
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 (Å^{2}) top  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) top
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)]
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Crystal data top
Be(H_{2}PO_{2})_{2}  D_{x} = 1.833 Mg m^{−}^{3} 
M_{r} = 138.98  Mo Kα radiation, λ = 0.71073 Å 
Tetragonal, P4_{1}2_{1}2  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 top
EnrafNonius CAD4 diffractometer  599 reflections with I > 2σ(I) 
Radiation source: finefocus sealed tube  R_{int} = 0.032 
Graphite monochromator  θ_{max} = 29.9°, θ_{min} = 4.1° 
2θ/θ scans  h = −6→6 
Absorption correction: empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989)  k = −4→7 
T_{min} = 0.761, T_{max} = 0.796  l = −27→28 
1372 measured reflections  3 standard reflections every 60 min 
699 independent reflections  intensity decay: none 
Refinement top
Refinement on F^{2}  Hydrogen site location: difference Fourier map 
Leastsquares matrix: full  All Hatom parameters refined 
R[F^{2} > 2σ(F^{2})] = 0.033  w = 1/[σ^{2}(F_{o}^{2}) + (0.0592P)^{2}] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
wR(F^{2}) = 0.098  (Δ/σ)_{max} < 0.001 
S = 1.08  Δρ_{max} = 0.28 e Å^{−}^{3} 
699 reflections  Δρ_{min} = −0.34 e Å^{−}^{3} 
43 parameters  Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
0 restraints  Extinction coefficient: 0.018 (6) 
Primary atom site location: structureinvariant direct methods  Absolute structure: Flack (1983), with xx Friedel pairs 
Secondary atom site location: difference Fourier map  Absolute structure parameter: 0.0 (4) 
Crystal data top
Be(H_{2}PO_{2})_{2}  Z = 4 
M_{r} = 138.98  Mo Kα radiation 
Tetragonal, P4_{1}2_{1}2  µ = 0.76 mm^{−}^{1} 
a = 5.0117 (5) Å  T = 293 K 
c = 20.051 (3) Å  0.4 × 0.3 × 0.3 mm 
V = 503.62 (10) Å^{3}  
Data collection top
EnrafNonius CAD4 diffractometer  599 reflections with I > 2σ(I) 
Absorption correction: empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989)  R_{int} = 0.032 
T_{min} = 0.761, T_{max} = 0.796  3 standard reflections every 60 min 
1372 measured reflections  intensity decay: none 
699 independent reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.033  All Hatom parameters refined 
wR(F^{2}) = 0.098  Δρ_{max} = 0.28 e Å^{−}^{3} 
S = 1.08  Δρ_{min} = −0.34 e Å^{−}^{3} 
699 reflections  Absolute structure: Flack (1983), with xx Friedel pairs 
43 parameters  Absolute structure parameter: 0.0 (4) 
0 restraints  
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 F^{2} against ALL reflections. The weighted Rfactor wR and goodness of fit S are based on F^{2}, conventional Rfactors R are based on F, with F set to zero for negative F^{2}. The threshold expression of F^{2} > σ(F^{2}) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. Rfactors based on F^{2} 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 (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
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 (Å^{2}) top  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) top
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. 
Experimental details
 (I)  (II) 
Crystal data 
Chemical formula  LiH_{2}PO_{2}  Be(H_{2}PO_{2})_{2} 
M_{r}  71.93  138.98 
Crystal system, space group  Monoclinic, C2/m  Tetragonal, P4_{1}2_{1}2 
Temperature (K)  293  293 
a, b, c (Å)  9.3557 (11), 5.3107 (7), 6.5432 (12)  5.0117 (5), 5.0117 (5), 20.051 (3) 
α, β, γ (°)  90, 108.259 (11), 90  90, 90, 90 
V (Å^{3})  308.73 (8)  503.62 (10) 
Z  4  4 
Radiation type  Mo Kα  Mo Kα 
µ (mm^{−}^{1})  0.62  0.76 
Crystal size (mm)  0.47 × 0.43 × 0.09  0.4 × 0.3 × 0.3 

Data collection 
Diffractometer  EnrafNonius CAD4 diffractometer  EnrafNonius CAD4 diffractometer 
Absorption correction  Empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989)  Empirical (using intensity measurements) (CADDAT; EnrafNonius, 1989) 
T_{min}, T_{max}  0.741, 0.946  0.761, 0.796 
No. of measured, independent and observed [I > 2σ(I)] reflections  430, 329, 306  1372, 699, 599 
R_{int}  0.041  0.032 
(sin θ/λ)_{max} (Å^{−}^{1})  0.609  0.702 

Refinement 
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S  0.038, 0.106, 1.15  0.033, 0.098, 1.08 
No. of reflections  329  699 
No. of parameters  29  43 
Hatom treatment  All Hatom parameters refined  All Hatom parameters refined 
Δρ_{max}, Δρ_{min} (e Å^{−}^{3})  0.38, −0.24  0.28, −0.34 
Absolute structure  ?  Flack (1983), with xx Friedel pairs 
Absolute structure parameter  ?  0.0 (4) 
Selected geometric parameters (Å, º) for (I) topLi—O1^{i}  1.933 (4)  P—O2  1.484 (2) 
Li—O2  1.936 (4)  P—H  1.35 (4) 
P—O1  1.478 (2)   
   
O1—P—O2  120.30 (15)  O1—P—H  109.7 (14) 
H^{ii}—P—H  92 (3)  O2—P—H  110.7 (15) 
Symmetry codes: (i) −x+1/2, −y+1/2, −z; (ii) x, −y+1, z. 
Selected geometric parameters (Å, º) for (II) topBe—O1  1.609 (3)  P—O2  1.4848 (19) 
Be—O2^{i}  1.603 (3)  P—H1  1.38 (2) 
P—O1  1.4888 (16)  P—H2  1.24 (3) 
   
O1—P—O2  114.78 (12)  O1—P—H2  110.3 (8) 
H1—P—H2  108.0 (14)  O2—P—H2  106.5 (8) 
Symmetry code: (i) y, x−1, −z. 
Previous studies of anhydrous hypophosphites include KH_{2}PO_{2}, RbH_{2}PO_{2} and CsH_{2}PO_{2} (Naumova Kuratieva Podberezskaya & Naumov, 2004), NH_{4}H_{2}PO_{2} (Zachariasen & Mooney, 1934), Ca(H_{2}PO_{2})_{2} (Goedkoop & Loopstra, 1959), CaNa(H_{2}PO_{2})_{3} (Matsuzaki & Iitaka, 1969), Cu(H_{2}PO_{2})_{2} (Naumov et al., 2002), Zn(H_{2}PO_{2})_{2} (Weakley, 1979; Tanner et al., 1997), GeCl(H_{2}PO_{2}) and SnCl(H_{2}PO_{2}) (Weakley & Watt, 1979), La(H_{2}PO_{2})_{3} (Tanner et al., 1999), Er(H_{2}PO_{2})_{3} (Aslanov et al., 1975), and U(H_{2}PO_{2})_{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(H_{2}PO_{2}) and Be(H_{2}PO_{2})_{2}. The hygroscopic nature of alkali and alkalineearth hypophosphites makes the growth of their crystals generally difficult. Nevertheless, crystals of these Li and Be hypophosphites were obtained and their structures determined by Xray diffraction. An initial report (Naumova Kuratieva Naumov & Podberezskaya, 2004) on the synthesis, growth conditions and crystal chemistry analysis of Li(H_{2}PO_{2}) was presented at the National Conference on Crystal Growth (NCCG2002, Moscow).
Both title structures are layered and contain metal cations in tetrahedral coordination by O. The coordination environments of the Li^{+} and Be^{2+} cations are similar in both structures but, due to the different cation/anion ratios, the environments of the hypophosphite anions are different. The H_{2}PO_{2}^{−} 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 Be^{2+} 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(H_{2}PO_{2}) and Be(H_{2}PO_{2})_{2}, respectively.