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The structure of the title compound, (NH4)2[Mg(H2O)6]3(HPO3)4, consists of [Mg(H2O)6]2+ and (NH4)+ cations and (HPO3)2- anions held together by an intricate network of hydrogen bonds involving all H atoms except for one linked directly to a P atom. The Mg2+ cations are octahedrally coordinated by six water molecules. One of the Mg atoms is located on a site with 2/m symmetry, whereas the other Mg atom and the P and N atoms occupy sites with m symmetry.
Supporting information
A sample of (NH4)2HPO3·H2O (2.5 g) was prepared by neutralization of phosphorous acid (H3PO3) with ammonium hydroxide. The sample was dissolved in water (10 ml) and this solution was then added to a 150 ml stirred aqueous solution of MgCl2 (containing less than 0.1 g of Mg). The resulting solution was slowly evaporated at 313 K. After a few days, white crystals appeared as rectangular prisms [Parallelepiped below?].
The H atoms were located in difference maps. Their positions were refined without any constraints, except for H5A/B, H6A/B, H7A/B and H9A/B, for which the O—H distances were restrained to 0.85 (2) Å. Individual isotropic displacement parameters were refined for the H atoms.
Data collection: SMART (Bruker, 1998); cell refinement: SAINT (Bruker, 1998); data reduction: SAINT; program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
Bis(ammonium) tris(hexaaquamagnesium) tetrakis(hydrogen phosphite)
top
Crystal data top
(NH4)2[Mg(H2O)6]3(HPO3)4 | F(000) = 796 |
Mr = 753.21 | Dx = 1.674 Mg m−3 |
Monoclinic, C2/m | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -C 2y | Cell parameters from 1017 reflections |
a = 34.364 (9) Å | θ = 3.0–25.3° |
b = 7.045 (2) Å | µ = 0.43 mm−1 |
c = 6.1736 (17) Å | T = 289 K |
β = 91.349 (4)° | Parallelepiped, white |
V = 1494.2 (7) Å3 | 0.5 × 0.35 × 0.25 mm |
Z = 2 | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 1677 reflections with I > 2σ(I) |
ω scans | Rint = 0.034 |
Absorption correction: empirical (using intensity measurements) (SADABS: Sheldrick, 1996) | θmax = 29.3°, θmin = 3.6° |
Tmin = 0.761, Tmax = 0.899 | h = −45→47 |
6601 measured reflections | k = −9→9 |
2083 independent reflections | l = −8→8 |
Refinement top
Refinement on F2 | 7 restraints |
Least-squares matrix: full | All H-atom parameters refined |
R[F2 > 2σ(F2)] = 0.033 | w = 1/[σ2(Fo2) + (0.0478P)2 + 0.9053P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.092 | (Δ/σ)max = 0.001 |
S = 1.03 | Δρmax = 0.29 e Å−3 |
2083 reflections | Δρmin = −0.39 e Å−3 |
158 parameters | |
Crystal data top
(NH4)2[Mg(H2O)6]3(HPO3)4 | V = 1494.2 (7) Å3 |
Mr = 753.21 | Z = 2 |
Monoclinic, C2/m | Mo Kα radiation |
a = 34.364 (9) Å | µ = 0.43 mm−1 |
b = 7.045 (2) Å | T = 289 K |
c = 6.1736 (17) Å | 0.5 × 0.35 × 0.25 mm |
β = 91.349 (4)° | |
Data collection top
Bruker SMART CCD area-detector diffractometer | 2083 independent reflections |
Absorption correction: empirical (using intensity measurements) (SADABS: Sheldrick, 1996) | 1677 reflections with I > 2σ(I) |
Tmin = 0.761, Tmax = 0.899 | Rint = 0.034 |
6601 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.033 | 7 restraints |
wR(F2) = 0.092 | All H-atom parameters refined |
S = 1.03 | Δρmax = 0.29 e Å−3 |
2083 reflections | Δρmin = −0.39 e Å−3 |
158 parameters | |
Special details top
Experimental. The crystal was positioned at a distance of 45 mm from the CCD area-detector entry. 3600 frames were recorded as an ω scan of 0.3 degrees. The integration (Lorentz and polarization correction, data reduction and processing) was carried out using the SAINT program of the SMART CCD software package (Bruker, 1998). The structure was solved by direct methods (SIR92; Altomare et al., 1993) and refined by a full-matrix least-squares procedure (SHELXL97; Sheldrick, 1997). |
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. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
N1 | 0.38276 (8) | −0.5000 | 0.9858 (5) | 0.0375 (5) | |
H11 | 0.3776 (8) | −0.601 (4) | 1.069 (4) | 0.064 (8)* | |
H12 | 0.3683 (9) | −0.5000 | 0.870 (5) | 0.028 (8)* | |
H13 | 0.4074 (13) | −0.5000 | 0.946 (6) | 0.066 (12)* | |
P1 | 0.452443 (16) | 0.0000 | 0.65602 (9) | 0.01871 (15) | |
O1 | 0.43576 (5) | 0.0000 | 0.8833 (3) | 0.0269 (4) | |
O2 | 0.44201 (3) | −0.17973 (16) | 0.52994 (18) | 0.0254 (3) | |
H1 | 0.4900 (7) | 0.0000 | 0.690 (4) | 0.021 (6)* | |
Mg2 | 0.5000 | −0.5000 | 1.0000 | 0.0215 (2) | |
O9 | 0.46426 (4) | −0.2927 (2) | 1.1279 (2) | 0.0316 (3) | |
H9A | 0.4569 (7) | −0.200 (4) | 1.053 (4) | 0.043 (6)* | |
H9B | 0.4596 (7) | −0.261 (3) | 1.257 (3) | 0.045 (7)* | |
O10 | 0.46310 (6) | −0.5000 | 0.7337 (3) | 0.0363 (5) | |
H10 | 0.4581 (7) | −0.593 (3) | 0.660 (4) | 0.046 (7)* | |
P2 | 0.295175 (16) | −0.5000 | 0.62182 (9) | 0.02015 (15) | |
H2 | 0.2799 (9) | −0.5000 | 0.428 (5) | 0.036 (8)* | |
O3 | 0.33953 (5) | −0.5000 | 0.5950 (3) | 0.0283 (4) | |
O4 | 0.28127 (3) | −0.31957 (17) | 0.73269 (19) | 0.0273 (3) | |
Mg1 | 0.33310 (2) | 0.0000 | 0.24863 (12) | 0.02177 (19) | |
O5 | 0.37051 (3) | −0.21943 (19) | 0.3490 (2) | 0.0279 (3) | |
O6 | 0.35909 (6) | 0.0000 | −0.0526 (3) | 0.0435 (5) | |
O7 | 0.29501 (4) | −0.2102 (2) | 0.1503 (2) | 0.0300 (3) | |
O8 | 0.30871 (5) | 0.0000 | 0.5567 (3) | 0.0276 (4) | |
H8 | 0.2971 (6) | 0.095 (3) | 0.609 (3) | 0.040 (6)* | |
H5A | 0.3601 (6) | −0.298 (3) | 0.429 (3) | 0.037 (6)* | |
H5B | 0.3923 (5) | −0.198 (3) | 0.401 (3) | 0.039 (6)* | |
H6A | 0.3828 (6) | 0.0000 | −0.080 (5) | 0.039 (8)* | |
H6B | 0.3476 (10) | 0.0000 | −0.169 (4) | 0.055 (11)* | |
H7A | 0.2939 (7) | −0.251 (3) | 0.025 (3) | 0.046 (7)* | |
H7B | 0.2726 (5) | −0.208 (4) | 0.193 (4) | 0.060 (8)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0341 (13) | 0.0435 (15) | 0.0348 (13) | 0.000 | −0.0044 (11) | 0.000 |
P1 | 0.0182 (3) | 0.0206 (3) | 0.0173 (3) | 0.000 | 0.0001 (2) | 0.000 |
O1 | 0.0279 (8) | 0.0341 (9) | 0.0187 (8) | 0.000 | 0.0028 (6) | 0.000 |
O2 | 0.0307 (6) | 0.0224 (6) | 0.0229 (6) | 0.0005 (5) | −0.0019 (5) | −0.0024 (4) |
Mg2 | 0.0239 (5) | 0.0221 (5) | 0.0185 (5) | 0.000 | −0.0008 (4) | 0.000 |
O9 | 0.0439 (8) | 0.0288 (6) | 0.0224 (6) | 0.0109 (6) | 0.0052 (5) | 0.0002 (5) |
O10 | 0.0575 (13) | 0.0210 (9) | 0.0296 (10) | 0.000 | −0.0190 (9) | 0.000 |
P2 | 0.0199 (3) | 0.0206 (3) | 0.0200 (3) | 0.000 | 0.0020 (2) | 0.000 |
O3 | 0.0202 (8) | 0.0330 (9) | 0.0317 (9) | 0.000 | 0.0034 (7) | 0.000 |
O4 | 0.0290 (6) | 0.0241 (6) | 0.0289 (6) | 0.0000 (5) | 0.0050 (5) | −0.0034 (5) |
Mg1 | 0.0183 (4) | 0.0256 (4) | 0.0214 (4) | 0.000 | 0.0004 (3) | 0.000 |
O5 | 0.0203 (6) | 0.0290 (7) | 0.0344 (7) | −0.0004 (5) | −0.0015 (5) | 0.0037 (5) |
O6 | 0.0231 (9) | 0.0866 (17) | 0.0207 (9) | 0.000 | 0.0014 (7) | 0.000 |
O7 | 0.0228 (6) | 0.0391 (7) | 0.0283 (7) | −0.0046 (5) | 0.0012 (5) | −0.0075 (6) |
O8 | 0.0325 (9) | 0.0234 (9) | 0.0272 (9) | 0.000 | 0.0079 (7) | 0.000 |
Geometric parameters (Å, º) top
P1—O2 | 1.5246 (12) | P2—O4iii | 1.5258 (12) |
P1—O2i | 1.5246 (12) | P2—O4 | 1.5258 (12) |
P1—O1 | 1.5280 (17) | P2—O3 | 1.5371 (17) |
P1—H1 | 1.30 (2) | P2—H2 | 1.30 (3) |
Mg2—O10 | 2.0526 (19) | Mg1—O7 | 2.0585 (14) |
Mg2—O10ii | 2.0526 (19) | Mg1—O7i | 2.0585 (14) |
Mg2—O9iii | 2.0764 (13) | Mg1—O6 | 2.082 (2) |
Mg2—O9 | 2.0764 (13) | Mg1—O5i | 2.0948 (14) |
Mg2—O9iv | 2.0764 (13) | Mg1—O5 | 2.0948 (14) |
Mg2—O9ii | 2.0764 (13) | Mg1—O8 | 2.0965 (19) |
| | | |
O2—P1—O2i | 112.30 (9) | O4iii—P2—O4 | 112.84 (10) |
O2—P1—O1 | 112.33 (6) | O4iii—P2—O3 | 111.73 (6) |
O2i—P1—O1 | 112.33 (6) | O4—P2—O3 | 111.73 (6) |
O1—P1—H1 | 104.1 (11) | O3—P2—H2 | 106.4 (14) |
O2—P1—H1 | 107.6 (5) | O4—P2—H2 | 106.9 (7) |
O2i—P1—H1 | 107.6 (5) | O4iii—P2—H2 | 106.9 (7) |
O10—Mg2—O10ii | 180.00 (10) | O7—Mg1—O7i | 92.00 (8) |
O10—Mg2—O9iii | 86.84 (6) | O7—Mg1—O6 | 91.13 (6) |
O10ii—Mg2—O9iii | 93.16 (6) | O7i—Mg1—O6 | 91.13 (6) |
O10—Mg2—O9 | 86.84 (6) | O7—Mg1—O5i | 178.34 (6) |
O10ii—Mg2—O9 | 93.16 (6) | O7i—Mg1—O5i | 86.44 (6) |
O9iii—Mg2—O9 | 89.41 (8) | O6—Mg1—O5i | 89.48 (6) |
O10—Mg2—O9iv | 93.16 (6) | O7—Mg1—O5 | 86.44 (6) |
O10ii—Mg2—O9iv | 86.84 (6) | O7i—Mg1—O5 | 178.34 (6) |
O9iii—Mg2—O9iv | 180.00 (6) | O6—Mg1—O5 | 89.48 (6) |
O9—Mg2—O9iv | 90.59 (8) | O5i—Mg1—O5 | 95.12 (8) |
O10—Mg2—O9ii | 93.16 (6) | O7—Mg1—O8 | 90.15 (6) |
O10ii—Mg2—O9ii | 86.84 (6) | O7i—Mg1—O8 | 90.15 (6) |
O9iii—Mg2—O9ii | 90.59 (8) | O6—Mg1—O8 | 178.16 (8) |
O9—Mg2—O9ii | 180.00 (6) | O5i—Mg1—O8 | 89.27 (6) |
O9iv—Mg2—O9ii | 89.41 (8) | O5—Mg1—O8 | 89.27 (6) |
Symmetry codes: (i) x, −y, z; (ii) −x+1, −y−1, −z+2; (iii) x, −y−1, z; (iv) −x+1, y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O5v | 0.89 (3) | 2.16 (3) | 3.026 (3) | 162 (2) |
N1—H12···O3 | 0.86 (3) | 1.94 (3) | 2.803 (3) | 175 (3) |
N1—H13···O10 | 0.89 (4) | 2.34 (4) | 3.201 (4) | 162 (3) |
O5—H5A···O3 | 0.83 (2) | 1.90 (2) | 2.7244 (18) | 174 (2) |
O5—H5B···O2 | 0.82 (2) | 1.87 (2) | 2.6898 (18) | 173 (2) |
O6—H6A···O1vi | 0.84 (2) | 1.84 (2) | 2.673 (3) | 175 (3) |
O6—H6B···O8vi | 0.81 (2) | 2.13 (2) | 2.936 (3) | 170 (4) |
O7—H7A···O4vi | 0.83 (2) | 1.91 (2) | 2.7212 (18) | 168 (2) |
O7—H7B···O4vii | 0.82 (2) | 1.93 (2) | 2.7435 (18) | 173 (3) |
O8—H8···O4i | 0.85 (2) | 1.85 (2) | 2.6807 (16) | 169 (2) |
O9—H9A···O1 | 0.83 (3) | 1.89 (3) | 2.7242 (18) | 175 (2) |
O9—H9B···O2viii | 0.84 (2) | 1.90 (2) | 2.7325 (18) | 172 (2) |
O10—H10···O2iii | 0.81 (2) | 1.87 (2) | 2.6749 (16) | 170 (2) |
Symmetry codes: (i) x, −y, z; (iii) x, −y−1, z; (v) x, −y−1, z+1; (vi) x, y, z−1; (vii) −x+1/2, −y−1/2, −z+1; (viii) x, y, z+1. |
Experimental details
Crystal data |
Chemical formula | (NH4)2[Mg(H2O)6]3(HPO3)4 |
Mr | 753.21 |
Crystal system, space group | Monoclinic, C2/m |
Temperature (K) | 289 |
a, b, c (Å) | 34.364 (9), 7.045 (2), 6.1736 (17) |
β (°) | 91.349 (4) |
V (Å3) | 1494.2 (7) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.43 |
Crystal size (mm) | 0.5 × 0.35 × 0.25 |
|
Data collection |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Empirical (using intensity measurements) (SADABS: Sheldrick, 1996) |
Tmin, Tmax | 0.761, 0.899 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6601, 2083, 1677 |
Rint | 0.034 |
(sin θ/λ)max (Å−1) | 0.688 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.033, 0.092, 1.03 |
No. of reflections | 2083 |
No. of parameters | 158 |
No. of restraints | 7 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 0.29, −0.39 |
Selected geometric parameters (Å, º) topP1—O2 | 1.5246 (12) | P2—O3 | 1.5371 (17) |
P1—O1 | 1.5280 (17) | Mg1—O7 | 2.0585 (14) |
Mg2—O10 | 2.0526 (19) | Mg1—O6 | 2.082 (2) |
Mg2—O9 | 2.0764 (13) | Mg1—O5 | 2.0948 (14) |
P2—O4 | 1.5258 (12) | Mg1—O8 | 2.0965 (19) |
| | | |
O2—P1—O2i | 112.30 (9) | O7—Mg1—O6 | 91.13 (6) |
O2—P1—O1 | 112.33 (6) | O6—Mg1—O5i | 89.48 (6) |
O10—Mg2—O9 | 86.84 (6) | O7—Mg1—O5 | 86.44 (6) |
O10ii—Mg2—O9 | 93.16 (6) | O6—Mg1—O5 | 89.48 (6) |
O9iii—Mg2—O9 | 89.41 (8) | O5i—Mg1—O5 | 95.12 (8) |
O9—Mg2—O9iv | 90.59 (8) | O7—Mg1—O8 | 90.15 (6) |
O4iii—P2—O4 | 112.84 (10) | O6—Mg1—O8 | 178.16 (8) |
O4—P2—O3 | 111.73 (6) | O5—Mg1—O8 | 89.27 (6) |
O7—Mg1—O7i | 92.00 (8) | | |
Symmetry codes: (i) x, −y, z; (ii) −x+1, −y−1, −z+2; (iii) x, −y−1, z; (iv) −x+1, y, −z+2. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H11···O5v | 0.89 (3) | 2.16 (3) | 3.026 (3) | 162 (2) |
N1—H12···O3 | 0.86 (3) | 1.94 (3) | 2.803 (3) | 175 (3) |
N1—H13···O10 | 0.89 (4) | 2.34 (4) | 3.201 (4) | 162 (3) |
O5—H5A···O3 | 0.830 (16) | 1.898 (16) | 2.7244 (18) | 174 (2) |
O5—H5B···O2 | 0.821 (16) | 1.873 (16) | 2.6898 (18) | 173 (2) |
O6—H6A···O1vi | 0.835 (18) | 1.841 (18) | 2.673 (3) | 175 (3) |
O6—H6B···O8vi | 0.814 (18) | 2.13 (2) | 2.936 (3) | 170 (4) |
O7—H7A···O4vi | 0.828 (16) | 1.906 (17) | 2.7212 (18) | 168 (2) |
O7—H7B···O4vii | 0.820 (17) | 1.928 (18) | 2.7435 (18) | 173 (3) |
O8—H8···O4i | 0.85 (2) | 1.85 (2) | 2.6807 (16) | 169 (2) |
O9—H9A···O1 | 0.83 (3) | 1.89 (3) | 2.7242 (18) | 175 (2) |
O9—H9B···O2viii | 0.843 (17) | 1.895 (17) | 2.7325 (18) | 172 (2) |
O10—H10···O2iii | 0.81 (2) | 1.87 (2) | 2.6749 (16) | 170 (2) |
Symmetry codes: (i) x, −y, z; (iii) x, −y−1, z; (v) x, −y−1, z+1; (vi) x, y, z−1; (vii) −x+1/2, −y−1/2, −z+1; (viii) x, y, z+1. |
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Phosphites of inorganic cations have been described in several papers, notably those containing the hydrogenophosphite HPO32− anion: Mg(HPO3)·6H2O (Corbridge, 1956), Cu(HPO3)·2H2O (Handlovič, 1969), Na2(HPO3)·5H2O (Colton & Henn, 1971), Sn(HPO3) (McDonald & Eriks, 1980), Sb2(HPO3)3 (Loub & Paulus, 1981), Ga2(HPO3)3·4H2O (Morris et al., 1992), [Mg(H2O)6]2+(HPO3)2− (Powell et al., 1994), Al2(HPO3)3 and Ga2(HPO3)3 (Morris et al., 1994), and Fe11(HPO3)8(OH)6 and Mn11(HPO3)8(OH)6 (Attfield et al., 1994). However, mixed phosphites have received less attention and only a few compounds containing the dihydrogenophosphite anion H2PO3− are known: CoNa(H2PO3)3·H2O (Kratochvíl et al., 1982), MnNa(H2PO3)3·H2O (Chmelíková et al., 1986), NaZn(H2PO3)3·H2O (Oursal et al., 2002) and NaMg(H2PO3)3·H2O (Oursal et al., 2003). To date, three mixed hydrogenophosphites have been reported, namely LiTl(HPO3) (Rafiq et al., 1981), and Zn3K2(HPO3)4 and Zn3Ba(HPO3)4·6H2O (Ortiz-Avila et al.,1989). In this paper, we report the crystal structure of a new mixed hydrogenphosphite, (NH4)[Mg(H2O)6]1.5(HPO3)2. This compound was isolated during an investigation of the interactions between diammonium hydrogenophosphite monohydrate, magnesium chloride hexahydrate and phosphorous acid.
The asymmetric unit contains two crystallographically distinct Mg sites (m and 2/m), two P sites (m), one N site (m), ten O sites (1 and m) and 15 H sites (1 and m). Symmetry operations generate the complete [Mg(H2O)6]2+ cations, (HPO3)2− anions and (NH4)+ cation, as depicted in Fig. 1. The hydrogenphosphite anions show their usual pseudo-pyramidal geometry [mean P—O = 1.529 (2) Å, mean O—P—O = 112.3 (1)°] (Harrison, 2003). The P—O bond length of 1.529 (2) Å is in good agreement with the distance of 1.519 Å obtained from theoretical calculations (Farrar & Trudeau, 1990) for an isolated phosphite anion. The P—H distances (1.296 and 1.294 Å) compare favourably with the value calculated by statistical evaluation of the geometry of inorganic phosphites (1.30 Å; Loub, 1991). They are also comparable with the P—H distances in Fe11(HPO3)8(OH)6 (1.298 Å) and Mn11(HPO3)8(OH)6 (1.29 Å; Attfield et al., 1994), and in NaMg(H2PO3)3·H2O (1.29 Å; Oursal et al., 2003), but are shorter than those found in other phosphites, such as LiTl(HPO3) (1.37 Å; Rafiq et al., 1981) and [Mg(H2O)6]2+(HPO3)2− (1.399 Å; Powell et al., 1994).
The coordination around the two independent Mg1 and Mg2 atoms is quite similar. Each Mg atom is strongly coordinated by six water molecules, forming a slightly distorted octahedron. The Mg2 environment has an unusual octahedral geometry, with two apical Mg—O distances [2.053 (2) Å] shorter than the four equatorial Mg—O distances [2.076 (1) Å].
Both water H atoms bonded to atoms O5, O7, O8, O9 and O10, and one H atom bonded to atom O6, are involved in hydrogen bonding to the O atoms of the phosphites. The other H atom on atom O6 is directed toward atom O8 of an adjacent magnesium hydrate group, with an O···O distance of 2.939 (3) Å indicating a moderately strong interaction. The tetrahedral coordination of each phosphite O atom (except atom O3 linked to P2) is fulfilled through hydrogen bonds from three different [Mg(H2O)6]2+ cations. Atom O3 is involved in two hydrogen bonds with two different water H atoms of [Mg(H2O)6]2+ cations and one hydrogen bond with the H atom of the NH4+ cation. Atom H1 (H2) directly bonded to P1 (P2) is over 2.7 (2.8) Å away from the closest O atom, indicating the absence of a hydrogen bond. The NH4+ cation is an almost regular tetrahedron, with four comparable N—H distances ranging from 0.86 to 0.89 Å and comparable angles varying from 106 to 111°. The H atoms are involved in two hydrogen bonds of equal length [2.17 (3) Å] with atoms O5(water) and O5i(water), and in two different hydrogen bonds with atoms O10(water) [2.36 (4) Å] and O3 [1.94 (3) Å].
The Mg—O bond lengths and O—Mg—O angles are generally as expected, with mean distances and angles of 2.080 Å and 89.78°, respectively, for Mg1, and 2.068 Å and 90°, respectively, for Mg2. These mean values agree well with those already found for [Mg(H2O)6]2+, notably in the phosphites NaMg(H2PO3)3·H2O (2.086 Å and 90.90°; Oursal et al., 2003) and [Mg(H2O)6]2+(HPO3)2− (2.079 Å and 89.63°; Powell et al., 1994), and in the phosphates MgHPO4·3H2O (2.083 Å and 89.82°; Sutor, 1967), MgNH4PO4·6H2O (2.087 Å and 90.03°; Abbona et al., 1984) and MgNH4PO4·6H2O (2.071 Å and 90.85°; Whitaker & Jeffery, 1970).