Heptamagnesium bis­(phosphate) tetra­kis­(hydrogen phosphate) with strong hydrogen bonds: Mg7(PO4)2(HPO4)4

Assani, A.; Saadi, M.; Zriouil, M.; El Ammari, L.

doi:10.1107/S1600536811036361

inorganic compounds

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Volume 67| Part 10| October 2011| Page i52

https://doi.org/10.1107/S1600536811036361

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Heptamagnesium bis(phosphate) tetrakis(hydrogen phosphate) with strong hydrogen bonds: Mg₇(PO₄)₂(HPO₄)₄

Abderrazzak Assani,^a ^* Mohamed Saadi,^a Mohammed Zriouil ^a and Lahcen El Ammari ^a

^aLaboratoire de Chimie du Solide Appliquée, Faculté des Sciences, Université Mohammed V-Agdal, Avenue Ibn Battouta, BP. 1014, Rabat, Morocco
^*Correspondence e-mail: abder_assani@yahoo.fr

(Received 5 September 2011; accepted 6 September 2011; online 14 September 2011)

The title compound, Mg₇(PO₄)₂(HPO₄)₄, was synthesized by the hydrothermal method. The structure is based on a framework of edge- and corner-sharing MgO₆ and MgO₄(OH)₂ octahedra, an MgO₅ polyhedron, PO₄ and PO₃(OH) tetrahedra. All atoms are in general positions except for one Mg atom, which is located on a crystallographic inversion centre. The OH groups, bridging Mg–(OH)–P, are involved in strong hydrogen bonds. Compounds with the general formula M₇(PO₄)₂(HPO₄)₄ (M = Mg, Mn, Fe and Co) are all isostructural with their homologue arsenate Mg₇(AsO₄)₂(HAsO₄)₄.

Related literature

For background to metal phosphates, see: Viter & Nagornyi (2009 ); Clearfield (1988 ); Trad et al. (2010 ). For the hydrothermal method, see: Assani et al. (2010 , 2011a ,b ). For isostructural compounds, see: Zhou et al. (2002 ); Riou et al. (1987 ); Rojo et al. (2002 ); Lightfoot & Cheetham (1988 ); Kolitsch & Bartu (2004 ).

Experimental

Crystal data

Mg₇(PO₄)₂(HPO₄)₄
M_r = 744.02
Triclinic, $[P \overline 1]$
a = 6.4204 (5) Å
b = 7.8489 (4) Å
c = 9.4315 (5) Å
α = 104.442 (3)°
β = 108.505 (5)°
γ = 101.189 (8)°
V = 416.70 (4) Å³
Z = 1
Mo Kα radiation
μ = 1.06 mm⁻¹
T = 296 K
0.16 × 0.10 × 0.07 mm

Data collection

Bruker X8 APEX Diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2005 ) T_min = 0.881, T_max = 0.929
9421 measured reflections
1923 independent reflections
1715 reflections with I > 2σ(I)
R_int = 0.036

Refinement

R[F² > 2σ(F²)] = 0.026
wR(F²) = 0.072
S = 1.07
1923 reflections
169 parameters
H-atom parameters constrained
Δρ_max = 0.43 e Å⁻³
Δρ_min = −0.42 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O4—H4⋯O7ⁱ	0.86	1.61	2.460 (2)	172
O12—H12⋯O10ⁱⁱ	0.86	1.80	2.656 (2)	171
Symmetry codes: (i) x, y-1, z; (ii) -x-1, -y+1, -z-1.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ) and DIAMOND (Brandenburg, 2006 ); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S1600536811036361/bt5638sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536811036361/bt5638Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S1600536811036361/bt5638Isup3.cml

checkCIF report

Comment top

Widespread studies are devoted to the metal phosphate owing to their impressive structural diversity and to their prospective applications in catalysis (Viter & Nagornyi, 2009), ion-exchangers (Clearfield, 1988)) and in batteries performance (Trad et al., (2010)). Mainly, our most attention has been paid to the hydrothermal synthesis of new metal based phosphate. Accordingly, we have recently succeed to obtain new phosphates, such as Ni₂Sr(PO₄)₂ 2H₂O (Assani et al. (2010)), AgMg₃(PO₄)(HPO₄)₂ (Assani et al. (2011b)) and Ag₂Ni₃(HPO₄)(PO₄)₂ (Assani et al. (2011a)).

Besides, the investigation of the MO—P₂O₅ systems (M=divalent cations) has allowed to isolate a new member of the metal phosphates, with a general formula M₇(PO₄)₂(HPO₄)₄. The present paper aims to develop the hydrothermal synthesis and the structural characterization of the Mg₇(PO₄)₂(HPO₄)₄ which is isostructural with Fe₇(PO₄)₂(HPO₄)₄ (Zhou et al. (2002)), Mn₇(PO₄)₂(HPO₄)₄ (Riou et al. (1987) and (Rojo et al. (2002)), Co₇(PO₄)₂(HPO₄)₄ (Lightfoot & Cheetham, (1988)) and with their homologue arsenate Mg₇(AsO₄)₂(HAsO₄)₄ (Kolitsch & Bartu, (2004)).

The crystal structure of Mg₇(PO₄)₂(HPO₄)₄ is built up from MgO₆, MgO₄(OH)₂ octahedra, MgO₅ polyhedron, PO₄ and PO₃(OH) tetrahedra, sharing corners and edges to form a three-dimensional framework as shown in Fig.1 and Fig.2. In the asymmetric unit, all atoms are in general positions except for atom Mg2, which is located at a crystallographic inversion centre (0, 0, 0). Each OH group is bonded to an Mg and an P atom. Atom Mg2 is located at the centre of an Mg2O₆ octahedron with significant bond-length distortion as shown in Table 1. In contrast, Mg1O₆ and Mg3O₄(OH)₂ represent less distorted octahedra, and atom Mg4 is surrounded by five O ligands, forming a distorted Mg4O₅ trigonal bipyramid. In this structure, each Mg1O₆ and Mg3O₆ octahedron shares an edge with its symmetrical to form a dimer. Both dimers, Mg1O₁₀ and Mg3O₁₀ are bound by Mg4O₅ by sharing two edges to form a zigzag chaine. The Mg2O₆ octahedron and PO₄ tetrahedra are linked to neighboring polyhedra by vertices. The three crystallographically independent P atoms show tetrahedral coordination. The PO₄ groups are relatively regular, although the two protonated groups, centred by P1 and P3, show a stronger angular and bond-length distortion in comparison with the unprotonated P2O₄ tetrahedron as shown in Table 1. Moreover the OH groups, bridging Mg–(OH)–P, are involved in strong hydrogen bonds (Table 2).

Related literature top

For rmetal phosphates, see: Viter & Nagornyi (2009); Clearfield (1988); Trad et al. (2010). For the hydrothermal method, see: Assani et al. (2010, 2011a,b). For isostructural compounds, see: Zhou et al. (2002); Riou et al. (1987); Rojo et al. (2002); Lightfoot & Cheetham (1988); Kolitsch & Bartu (2004).

Experimental top

The crystals of the title compound is isolated from the hydrothermal treatment of the reaction mixture of magnesium oxide (MgO) and 85%wt phosphoric acid (H₃PO₄) in the nominal proportion corresponding to the molar ratio Mg: P = 7:6. The hydrothermal reaction was conducted in a 23 ml Teflon-lined autoclave, filled to 50% with distilled water and under autogenously pressure at 468 K for two days. After being filtered off, washed with deionized water and air dried, the reaction product consists of a white powder and colourless parallelepipedic crystals corresponding to the title compound.

Structure description top

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia,1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).

Figures top

Fig. 1. Partial plot of Mg₇(PO₄)₂(HPO₄)₄ crystal structure. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: (i) -x - 1, -y + 1, -z - 1; (ii) -x, -y + 1, -z; (iii) x - 1, y, z; (iv) x, y - 1, z; (v) -x, -y, -z; (vi) -x - 1, -y, -z - 1; (vii) x + 1, y, z + 1; (viii) -x, -y, -z - 1; (ix) -x, -y + 1, -z - 1; (x) x + 1, y, z; (xi) x, y + 1, z; (xii) x - 1, y, z - 1.

Fig. 2. A three-dimensional polyhedral view of the crystal structure of the Mg₇(PO₄)₂(HPO₄)₄ showing polyhedra linkage.

Heptamagnesium bis(phosphate) tetrakis(hydrogen phosphate) top

Crystal data top

Mg₇(PO₄)₂(HPO₄)₄	Z = 1
M_r = 744.02	F(000) = 370
Triclinic, P1	D_x = 2.965 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.4204 (5) Å	Cell parameters from 1923 reflections
b = 7.8489 (4) Å	θ = 2.4–27.6°
c = 9.4315 (5) Å	µ = 1.06 mm⁻¹
α = 104.442 (3)°	T = 296 K
β = 108.505 (5)°	Parallelepipedic, colourless
γ = 101.189 (8)°	0.16 × 0.10 × 0.07 mm
V = 416.70 (4) Å³

Data collection top

Bruker X8 APEX Diffractometer	1923 independent reflections
Radiation source: fine-focus sealed tube	1715 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.036
φ and ω scans	θ_max = 27.6°, θ_min = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −8→8
T_min = 0.881, T_max = 0.929	k = −10→10
9421 measured reflections	l = −11→12

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)] = 0.026	Hydrogen site location: difference Fourier map
wR(F²) = 0.072	H-atom parameters constrained
S = 1.07	w = 1/[σ²(F_o²) + (0.0325P)² + 0.6237P] where P = (F_o² + 2F_c²)/3
1923 reflections	(Δ/σ)_max < 0.001
169 parameters	Δρ_max = 0.43 e Å⁻³
0 restraints	Δρ_min = −0.42 e Å⁻³

Crystal data top

Mg₇(PO₄)₂(HPO₄)₄	γ = 101.189 (8)°
M_r = 744.02	V = 416.70 (4) Å³
Triclinic, P1	Z = 1
a = 6.4204 (5) Å	Mo Kα radiation
b = 7.8489 (4) Å	µ = 1.06 mm⁻¹
c = 9.4315 (5) Å	T = 296 K
α = 104.442 (3)°	0.16 × 0.10 × 0.07 mm
β = 108.505 (5)°

Data collection top

Bruker X8 APEX Diffractometer	1923 independent reflections
Absorption correction: multi-scan (SADABS; Bruker, 2005)	1715 reflections with I > 2σ(I)
T_min = 0.881, T_max = 0.929	R_int = 0.036
9421 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.026	0 restraints
wR(F²) = 0.072	H-atom parameters constrained
S = 1.07	Δρ_max = 0.43 e Å⁻³
1923 reflections	Δρ_min = −0.42 e Å⁻³
169 parameters

Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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	U_iso*/U_eq
Mg1	−0.38348 (12)	0.54390 (10)	−0.10950 (8)	0.00639 (17)
Mg2	0.0000	0.0000	0.0000	0.0094 (2)
Mg3	−0.05324 (13)	0.28758 (10)	−0.51536 (9)	0.00821 (17)
Mg4	−0.27778 (13)	0.19081 (11)	−0.28530 (9)	0.00902 (17)
P1	0.22691 (9)	0.14512 (8)	−0.22413 (6)	0.00561 (13)
P2	0.08899 (9)	0.58025 (7)	−0.17255 (6)	0.00465 (13)
P3	−0.59090 (9)	0.23141 (8)	−0.62865 (7)	0.00658 (14)
O1	0.0189 (3)	0.1762 (2)	−0.33779 (18)	0.0081 (3)
O2	0.2208 (3)	0.1877 (2)	−0.05694 (18)	0.0074 (3)
O3	0.4517 (3)	0.2446 (2)	−0.22968 (18)	0.0077 (3)
O4	0.2013 (3)	−0.0667 (2)	−0.27972 (18)	0.0091 (3)
H4	0.1828	−0.1148	−0.2104	0.011*
O5	0.3069 (3)	0.5385 (2)	−0.08555 (18)	0.0068 (3)
O6	0.0589 (3)	0.5452 (2)	−0.34643 (18)	0.0073 (3)
O7	0.1098 (3)	0.7857 (2)	−0.09645 (19)	0.0094 (3)
O8	−0.1240 (3)	0.4602 (2)	−0.16487 (18)	0.0070 (3)
O9	−0.3803 (3)	0.2112 (2)	−0.50853 (19)	0.0104 (3)
O10	−0.5267 (3)	0.3827 (2)	−0.69363 (19)	0.0106 (3)
O11	−0.7360 (3)	0.0488 (2)	−0.76029 (19)	0.0097 (3)
O12	−0.7344 (3)	0.2950 (2)	−0.52719 (19)	0.0111 (3)
H12	−0.6495	0.3935	−0.4485	0.013*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Mg1	0.0064 (4)	0.0077 (4)	0.0058 (4)	0.0022 (3)	0.0028 (3)	0.0028 (3)
Mg2	0.0120 (5)	0.0086 (5)	0.0095 (5)	0.0035 (4)	0.0061 (4)	0.0034 (4)
Mg3	0.0091 (4)	0.0083 (4)	0.0076 (4)	0.0021 (3)	0.0037 (3)	0.0029 (3)
Mg4	0.0093 (4)	0.0082 (4)	0.0104 (4)	0.0027 (3)	0.0047 (3)	0.0031 (3)
P1	0.0055 (3)	0.0055 (3)	0.0056 (3)	0.0011 (2)	0.0024 (2)	0.0016 (2)
P2	0.0045 (3)	0.0052 (3)	0.0047 (3)	0.0017 (2)	0.0019 (2)	0.0020 (2)
P3	0.0058 (3)	0.0073 (3)	0.0067 (3)	0.0019 (2)	0.0023 (2)	0.0025 (2)
O1	0.0056 (7)	0.0103 (8)	0.0084 (8)	0.0024 (6)	0.0019 (6)	0.0041 (6)
O2	0.0086 (7)	0.0070 (7)	0.0056 (7)	0.0010 (6)	0.0031 (6)	0.0008 (6)
O3	0.0056 (7)	0.0078 (7)	0.0088 (7)	−0.0002 (6)	0.0037 (6)	0.0019 (6)
O4	0.0133 (8)	0.0067 (7)	0.0085 (8)	0.0025 (6)	0.0057 (6)	0.0030 (6)
O5	0.0053 (7)	0.0094 (7)	0.0068 (7)	0.0034 (6)	0.0024 (6)	0.0034 (6)
O6	0.0097 (7)	0.0081 (7)	0.0053 (7)	0.0036 (6)	0.0035 (6)	0.0030 (6)
O7	0.0119 (8)	0.0060 (7)	0.0109 (8)	0.0038 (6)	0.0050 (6)	0.0021 (6)
O8	0.0049 (7)	0.0071 (7)	0.0091 (7)	0.0010 (6)	0.0037 (6)	0.0020 (6)
O9	0.0085 (8)	0.0157 (8)	0.0086 (8)	0.0059 (6)	0.0030 (6)	0.0052 (6)
O10	0.0117 (8)	0.0093 (8)	0.0087 (8)	−0.0002 (6)	0.0018 (6)	0.0048 (6)
O11	0.0098 (7)	0.0073 (7)	0.0102 (8)	0.0014 (6)	0.0025 (6)	0.0025 (6)
O12	0.0084 (8)	0.0137 (8)	0.0099 (8)	0.0037 (6)	0.0042 (6)	0.0010 (6)

Geometric parameters (Å, º) top

Mg1—O10ⁱ	2.0235 (17)	P1—O2	1.5431 (16)
Mg1—O5ⁱⁱ	2.0462 (17)	P1—O4	1.5718 (16)
Mg1—O5ⁱⁱⁱ	2.0643 (17)	P2—O5	1.5237 (16)
Mg1—O8	2.0698 (17)	P2—O6	1.5350 (16)
Mg1—O2ⁱⁱ	2.1093 (17)	P2—O8	1.5362 (16)
Mg1—O3ⁱⁱⁱ	2.2065 (17)	P2—O7	1.5533 (16)
Mg2—O7^iv	2.0630 (16)	P3—O10	1.5131 (16)
Mg2—O7ⁱⁱ	2.0630 (16)	P3—O11	1.5245 (17)
Mg2—O2	2.1296 (15)	P3—O9	1.5287 (16)
Mg2—O2^v	2.1296 (15)	P3—O12	1.5853 (17)
Mg2—O11^vi	2.2395 (16)	O2—Mg1ⁱⁱ	2.1093 (17)
Mg2—O11^vii	2.2395 (16)	O3—Mg4^x	2.0549 (17)
Mg3—O4^viii	2.0415 (17)	O3—Mg1^x	2.2065 (17)
Mg3—O1	2.0443 (17)	O4—Mg3^viii	2.0415 (17)
Mg3—O6	2.0606 (17)	O4—H4	0.8601
Mg3—O6^ix	2.0649 (17)	O5—Mg1ⁱⁱ	2.0462 (17)
Mg3—O12^x	2.0759 (17)	O5—Mg1^x	2.0643 (17)
Mg3—O9	2.0954 (17)	O6—Mg3^ix	2.0649 (17)
Mg4—O8	2.0041 (17)	O7—Mg2^xi	2.0630 (16)
Mg4—O11^vi	2.0426 (18)	O10—Mg1ⁱ	2.0235 (17)
Mg4—O9	2.0544 (17)	O11—Mg4^vi	2.0426 (18)
Mg4—O3ⁱⁱⁱ	2.0549 (17)	O11—Mg2^xii	2.2395 (16)
Mg4—O1	2.1312 (17)	O12—Mg3ⁱⁱⁱ	2.0759 (17)
P1—O3	1.5252 (16)	O12—H12	0.8600
P1—O1	1.5297 (16)

O10ⁱ—Mg1—O5ⁱⁱ	177.45 (7)	O1—Mg3—O12^x	90.91 (7)
O10ⁱ—Mg1—O5ⁱⁱⁱ	93.60 (7)	O6—Mg3—O12^x	95.01 (7)
O5ⁱⁱ—Mg1—O5ⁱⁱⁱ	84.54 (7)	O6^ix—Mg3—O12^x	82.93 (7)
O10ⁱ—Mg1—O8	89.62 (7)	O4^viii—Mg3—O9	82.41 (7)
O5ⁱⁱ—Mg1—O8	91.62 (7)	O1—Mg3—O9	80.21 (7)
O5ⁱⁱⁱ—Mg1—O8	161.77 (7)	O6—Mg3—O9	96.14 (7)
O10ⁱ—Mg1—O2ⁱⁱ	97.16 (7)	O6^ix—Mg3—O9	108.15 (7)
O5ⁱⁱ—Mg1—O2ⁱⁱ	84.67 (7)	O12^x—Mg3—O9	165.63 (8)
O5ⁱⁱⁱ—Mg1—O2ⁱⁱ	92.32 (7)	O8—Mg4—O11^vi	135.86 (7)
O8—Mg1—O2ⁱⁱ	105.09 (7)	O8—Mg4—O9	97.00 (7)
O10ⁱ—Mg1—O3ⁱⁱⁱ	96.93 (7)	O11^vi—Mg4—O9	124.27 (7)
O5ⁱⁱ—Mg1—O3ⁱⁱⁱ	81.15 (6)	O8—Mg4—O3ⁱⁱⁱ	83.43 (7)
O5ⁱⁱⁱ—Mg1—O3ⁱⁱⁱ	83.53 (6)	O11^vi—Mg4—O3ⁱⁱⁱ	102.94 (7)
O8—Mg1—O3ⁱⁱⁱ	78.27 (6)	O9—Mg4—O3ⁱⁱⁱ	98.66 (7)
O2ⁱⁱ—Mg1—O3ⁱⁱⁱ	165.53 (7)	O8—Mg4—O1	88.96 (7)
O7^iv—Mg2—O7ⁱⁱ	180.00 (7)	O11^vi—Mg4—O1	84.69 (7)
O7^iv—Mg2—O2	91.18 (6)	O9—Mg4—O1	79.14 (7)
O7ⁱⁱ—Mg2—O2	88.82 (6)	O3ⁱⁱⁱ—Mg4—O1	171.78 (7)
O7^iv—Mg2—O2^v	88.82 (6)	O3—P1—O1	111.79 (9)
O7ⁱⁱ—Mg2—O2^v	91.18 (6)	O3—P1—O2	114.92 (9)
O2—Mg2—O2^v	180.00 (7)	O1—P1—O2	110.31 (9)
O7^iv—Mg2—O11^vi	90.17 (6)	O3—P1—O4	106.96 (9)
O7ⁱⁱ—Mg2—O11^vi	89.83 (6)	O1—P1—O4	107.87 (9)
O2—Mg2—O11^vi	85.85 (6)	O2—P1—O4	104.43 (9)
O2^v—Mg2—O11^vi	94.15 (6)	O5—P2—O6	109.03 (9)
O7^iv—Mg2—O11^vii	89.83 (6)	O5—P2—O8	111.40 (9)
O7ⁱⁱ—Mg2—O11^vii	90.17 (6)	O6—P2—O8	109.62 (9)
O2—Mg2—O11^vii	94.15 (6)	O5—P2—O7	109.95 (9)
O2^v—Mg2—O11^vii	85.85 (6)	O6—P2—O7	108.49 (9)
O11^vi—Mg2—O11^vii	180.00 (8)	O8—P2—O7	108.30 (9)
O4^viii—Mg3—O1	104.92 (7)	O10—P3—O11	112.06 (9)
O4^viii—Mg3—O6	165.27 (8)	O10—P3—O9	112.08 (9)
O1—Mg3—O6	89.19 (7)	O11—P3—O9	111.85 (9)
O4^viii—Mg3—O6^ix	87.80 (7)	O10—P3—O12	107.28 (9)
O1—Mg3—O6^ix	165.83 (8)	O11—P3—O12	109.21 (9)
O6—Mg3—O6^ix	78.70 (7)	O9—P3—O12	103.90 (9)
O4^viii—Mg3—O12^x	89.06 (7)

Symmetry codes: (i) −x−1, −y+1, −z−1; (ii) −x, −y+1, −z; (iii) x−1, y, z; (iv) x, y−1, z; (v) −x, −y, −z; (vi) −x−1, −y, −z−1; (vii) x+1, y, z+1; (viii) −x, −y, −z−1; (ix) −x, −y+1, −z−1; (x) x+1, y, z; (xi) x, y+1, z; (xii) x−1, y, z−1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O7^iv	0.86	1.61	2.460 (2)	172
O12—H12···O10ⁱ	0.86	1.80	2.656 (2)	171

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

Experimental details

Crystal data
Chemical formula	Mg₇(PO₄)₂(HPO₄)₄
M_r	744.02
Crystal system, space group	Triclinic, P1
Temperature (K)	296
a, b, c (Å)	6.4204 (5), 7.8489 (4), 9.4315 (5)
α, β, γ (°)	104.442 (3), 108.505 (5), 101.189 (8)
V (Å³)	416.70 (4)
Z	1
Radiation type	Mo Kα
µ (mm⁻¹)	1.06
Crystal size (mm)	0.16 × 0.10 × 0.07

Data collection
Diffractometer	Bruker X8 APEX Diffractometer
Absorption correction	Multi-scan (SADABS; Bruker, 2005)
T_min, T_max	0.881, 0.929
No. of measured, independent and observed [I > 2σ(I)] reflections	9421, 1923, 1715
R_int	0.036
(sin θ/λ)_max (Å⁻¹)	0.651

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.072, 1.07
No. of reflections	1923
No. of parameters	169
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.43, −0.42

Computer programs: APEX2 (Bruker, 2005), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia,1997) and DIAMOND (Brandenburg, 2006), WinGX publication routines (Farrugia, 1999).

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O7ⁱ	0.86	1.61	2.460 (2)	171.8
O12—H12···O10ⁱⁱ	0.86	1.80	2.656 (2)	171.1

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

Acknowledgements

The authors thank the Unit of Support for Technical and Scientific Research (UATRS, CNRST) for the X-ray measurements.

References

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