Crystal structure of alluaudite-type NaMg3(HPO4)2(PO4).

The title compound, sodium trimagnesium bis-(hydrogen phosphate) phosphate, was obtained under hydro-thermal conditions. In the crystal, two types of [MgO6] octa-hedra, one with point group symmetry 2, share edges to build chains extending parallel to [10-1]. These chains are linked together by two kinds of phosphate tetra-hedra, HPO4 and PO4, the latter with point group symmetry 2. The three-dimensional framework delimits two different types of channels extending along [001]. One channel hosts the Na(+) cations (site symmetry 2) surrounded by eight O atoms, with Na-O bond lengths varying between 2.2974 (13) and 2.922 (2) Å. The OH group of the HPO4 tetra-hedron points into the other type of channel and exhibits a strong hydrogen bond to an O atom of the PO4 tetra-hedron on the opposite side.

Chemical context

By means of hydro­thermal processes (Demazeau, 2008 ▸; Yoshimura & Byrappa, 2008 ▸), we have previously succeeded in the isolation of the mixed-valence manganese phosphates MMnII 2MnIII(PO4)3 (M = Ba, Pb, Sr) adopting the α-CrPO4 structure type (Assani et al., 2013 ▸; Alhakmi et al., 2013a ▸,b ▸). In addition, within the pseudo-ternary systems Ag2O–MO–P2O5, hydro­thermal syntheses have allowed us to obtain other α-CrPO4 isotype phosphates, viz. Ag2 M 3(HPO4)(PO4)2 (M = Co, Ni) while AgMg3(HPO4)2(PO4) is found to adopt the alluaudite structure type (Assani et al., 2011a ▸,b ▸,c ▸). Other hydro­thermally grown phosphates with the alluaudite structure include AgCo3(HPO4)2(PO4) (Guesmi & Driss, 2002 ▸), AgNi3(HPO4)2(PO4) (Ben Smail & Jouini, 2002 ▸), AMn3(HPO4)2(PO4) (A = Na, Ag) (Leroux et al., 1995a ▸,b ▸) and NaCo3(HPO4)2(PO4) (Lii & Shih, 1994 ▸). Phosphates belonging to either the α-CrPO4 or alluaudite structure type or derivatives thereof are still in the focus of research owing to their promising applications as battery materials (Trad et al., 2010 ▸; Essehli et al., 2015a ▸,b ▸; Huang et al., 2015 ▸).

The crystal structures of alluaudite-type phosphates exhibit channels in which the monovalent cations are localized. Indeed, this is strongly required for conductivity properties. The crystal structure of alluaudite can be formulated by the general formula (A1)(A2)(M1)(M2)2(PO4)3, (Moore & Ito, 1979 ▸). The two A sites can be occupied by either mono- or divalent medium-sized cations while the two M cationic sites correspond to an octa­hedral environment generally occupied by transition metal cations. On the basis of literature research, it has been shown that the hydro­thermal process allows, in general, stoechiometric phases to be obtained while solid-state reactions give rather a statistical distribution of cations on either the A or M sites, leading to non-stoechiometric compounds (Bouraima et al., 2015 ▸; Khmiyas et al., 2015 ▸).

In line with our focus of inter­est, we hydro­thermally synthesized the compound NaMg3(PO4)(HPO4)2 and report here its crystal structure.

Structural commentary

The principal building units of the allaudite structure of the title compound are represented in Fig. 1 ▸. The three atoms Mg1, Na1 and P1 are located on a twofold rotation axis (Wyckoff position 4e). Selected inter­atomic distances are compiled in Table 1 ▸. The three-dimensional framework of this structure consists of kinked chains of edge-sharing MgO6 octa­hedra running parallel to [10]. The chains are held together by regular P1O4 phosphate groups, forming sheets perpendicular to [010], as shown in Fig. 2 ▸. The stacked sheets delimit two types of channels along [001]. One of the channels is occupied by Na+ cations surrounded by eight oxygen atoms (Table 1 ▸), whereas the second channel contains the hydrogen atoms of the HP2O4 tetra­hedra, as shown in Fig. 3 ▸. They form strong hydrogen bonds (Table 2 ▸, Figs. 1 ▸ and 3 ▸) with one of the oxygen atoms of PO4 tetra­hedra on opposite sides.

Figure 1

The principal building units in the structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are indicated by dashed lines [Symmetry codes: (i) x + , y + , z; (ii) −x + , y + , −z + ; (iii) −x + , −y + , −z + 1; (iv) −x + , −y + , −z; (v) −x + 1, −y + 1, −z; (vi) −x + 1, y, −z + ; (vii) x, −y + 1, z + ; (viii) x − , −y + , z − ; (ix) −x + 2, y, −z + ; (x) −x + 2, −y + 1, −z + 1; (xi) x + , −y + , z + ; (xii) −x + , −y + , −z + 1; (xiii) x, −y + 1, z − .]

Table 1

Selected bond lengths ()

Mg1O3i	2.1224(13)	Na1O3	2.8840(19)
Mg1O1ii	2.1312(12)	Na1O1vii	2.922(2)
Mg1O4	2.1669(14)	P1O1viii	1.5372(12)
Mg2O6	2.0234(13)	P1O1	1.5372(12)
Mg2O3ii	2.0686(13)	P1O2viii	1.5476(13)
Mg2O2	2.0696(14)	P1O2	1.5476(13)
Mg2O5iii	2.0729(13)	P2O5	1.5234(12)
Mg2O5iv	2.0955(13)	P2O6	1.5263(12)
Mg2O1v	2.1153(14)	P2O3	1.5349(13)
Na1O6	2.2974(13)	P2O4	1.5806(13)
Na1O6vi	2.4386(13)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) ; (vii) ; (viii) .

Figure 2

A sheet resulting from the linkage of kinked chains via vertices of PO4 tetra­hedra.

Figure 3

Polyhedral representation of the NaMg3(HPO4)2(PO4) structure showing channels along [001]. The O—H⋯O hydrogen bonds are indicated by dashed lines.

Table 2

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
O4H4O2	0.93	1.57	2.4932(17)	174

Synthesis and crystallization

Colourless parallelepiped-shaped crystals of the title compound were grown under hydro­thermal conditions, starting from a mixture of Na4P2O7·10H2O, MgO and H3PO4 (85 wt%) in the molar ratio Na4P2O7·10H2O:MgO:H3PO4 = 1:3:3. The hydro­thermal reaction was conducted in a 23 ml Teflon-lined autoclave, filled to 50% with distilled water and under autogenous pressure at 483 K for four days.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. The minimum and maximum electron densities are located 0.71 and 0.17 Å from O5 and H4, respectively. The O–bound H atom was initially located in a difference map and refined with an O—H distance restraint of 0.93 Å, and with U iso(H) = 1.5U eq(O).

Table 3

Experimental details

Crystal data
Chemical formula	NaMg3(HPO4)2(PO4)
M r	382.85
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c ()	11.8064(6), 12.0625(7), 6.4969(4)
()	113.805(2)
V (3)	846.54(8)
Z	4
Radiation type	Mo K
(mm1)	1.06
Crystal size (mm)	0.36 0.24 0.18
Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Bruker, 2009 ▸)
T min, T max	0.504, 0.748
No. of measured, independent and observed [I > 2(I)] reflections	9797, 1291, 1138
R int	0.038
(sin /)max (1)	0.714
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.025, 0.072, 1.09
No. of reflections	1291
No. of parameters	88
H-atom treatment	H-atom parameters constrained
max, min (e 3)	0.57, 0.54

Computer programs: APEX2 and SAINT (Bruker, 2009 ▸), SHELXS (Sheldrick, 2008 ▸), SHELXL2013 (Sheldrick, 2015 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸). DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S205698901501155X/wm5174sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901501155X/wm5174Isup2.hkl

CCDC reference: 1406819

Additional supporting information: crystallographic information; 3D view; checkCIF report

NaMg3(HPO4)2(PO4)	F(000) = 760
Mr = 382.85	Dx = 3.004 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.8064 (6) Å	Cell parameters from 1291 reflections
b = 12.0625 (7) Å	θ = 2.5–30.5°
c = 6.4969 (4) Å	µ = 1.06 mm−1
β = 113.805 (2)°	T = 296 K
V = 846.54 (8) Å3	Block, colourless
Z = 4	0.36 × 0.24 × 0.18 mm

Bruker X8 APEX diffractometer	1291 independent reflections
Radiation source: fine-focus sealed tube	1138 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.038
φ and ω scans	θmax = 30.5°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −16→16
Tmin = 0.504, Tmax = 0.748	k = −17→17
9797 measured reflections	l = −9→8

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.025	H-atom parameters constrained
wR(F2) = 0.072	w = 1/[σ2(Fo2) + (0.0362P)2 + 1.4203P] where P = (Fo2 + 2Fc2)/3
S = 1.09	(Δ/σ)max < 0.001
1291 reflections	Δρmax = 0.57 e Å−3
88 parameters	Δρmin = −0.54 e Å−3

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.

	x	y	z	Uiso*/Ueq
Mg1	0.0000	0.27947 (7)	0.2500	0.00857 (18)
Mg2	0.29000 (6)	0.66219 (5)	0.37489 (10)	0.00643 (14)
Na1	0.5000	0.52321 (14)	0.7500	0.0308 (4)
P1	0.0000	0.68659 (5)	0.2500	0.00564 (14)
P2	0.28093 (4)	0.38887 (3)	0.38603 (7)	0.00494 (11)
O1	0.03662 (11)	0.75858 (10)	0.4624 (2)	0.0078 (2)
O2	0.10795 (12)	0.61003 (10)	0.2634 (2)	0.0084 (2)
O3	0.34567 (12)	0.32859 (10)	0.6116 (2)	0.0073 (2)
O4	0.14051 (11)	0.40754 (10)	0.3420 (2)	0.0085 (2)
H4	0.1241	0.4816	0.3033	0.013*
O5	0.28443 (11)	0.32046 (10)	0.1916 (2)	0.0068 (2)
O6	0.34273 (12)	0.50140 (10)	0.4000 (2)	0.0076 (2)

	U11	U22	U33	U12	U13	U23
Mg1	0.0081 (4)	0.0088 (4)	0.0094 (4)	0.000	0.0041 (3)	0.000
Mg2	0.0073 (3)	0.0057 (3)	0.0067 (3)	0.0004 (2)	0.0031 (2)	0.0001 (2)
Na1	0.0118 (6)	0.0691 (11)	0.0091 (6)	0.000	0.0016 (5)	0.000
P1	0.0051 (3)	0.0063 (3)	0.0044 (3)	0.000	0.0007 (2)	0.000
P2	0.0060 (2)	0.00431 (19)	0.0043 (2)	−0.00006 (14)	0.00177 (16)	−0.00011 (14)
O1	0.0063 (6)	0.0110 (5)	0.0054 (5)	−0.0010 (4)	0.0014 (5)	−0.0022 (4)
O2	0.0060 (6)	0.0073 (5)	0.0114 (6)	0.0010 (4)	0.0031 (5)	−0.0007 (4)
O3	0.0086 (6)	0.0080 (5)	0.0049 (5)	0.0020 (4)	0.0024 (5)	0.0016 (4)
O4	0.0073 (6)	0.0058 (5)	0.0131 (6)	0.0009 (4)	0.0048 (5)	0.0004 (5)
O5	0.0077 (6)	0.0077 (5)	0.0052 (5)	0.0003 (4)	0.0028 (5)	−0.0009 (4)
O6	0.0083 (6)	0.0051 (5)	0.0093 (6)	−0.0014 (4)	0.0035 (5)	−0.0002 (4)

Mg1—O3i	2.1224 (13)	Na1—O6x	2.4386 (13)
Mg1—O3ii	2.1224 (13)	Na1—O3	2.8840 (19)
Mg1—O1iii	2.1312 (12)	Na1—O3ix	2.8840 (19)
Mg1—O1iv	2.1312 (12)	Na1—O1xi	2.922 (2)
Mg1—O4v	2.1669 (14)	Na1—O1viii	2.922 (2)
Mg1—O4	2.1669 (14)	P1—O1v	1.5372 (12)
Mg2—O6	2.0234 (13)	P1—O1	1.5372 (12)
Mg2—O3iii	2.0686 (13)	P1—O2v	1.5476 (13)
Mg2—O2	2.0696 (14)	P1—O2	1.5476 (13)
Mg2—O5vi	2.0729 (13)	P2—O5	1.5234 (12)
Mg2—O5vii	2.0955 (13)	P2—O6	1.5263 (12)
Mg2—O1viii	2.1153 (14)	P2—O3	1.5349 (13)
Na1—O6	2.2974 (13)	P2—O4	1.5806 (13)
Na1—O6ix	2.2974 (13)	O4—H4	0.9269
Na1—O6vii	2.4386 (13)
O3i—Mg1—O3ii	104.23 (8)	O6vii—Na1—O6x	166.01 (10)
O3i—Mg1—O1iii	86.53 (5)	O6—Na1—O3	56.06 (5)
O3ii—Mg1—O1iii	78.23 (5)	O6ix—Na1—O3	111.84 (7)
O3i—Mg1—O1iv	78.23 (5)	O6vii—Na1—O3	62.51 (5)
O3ii—Mg1—O1iv	86.53 (5)	O6x—Na1—O3	105.27 (6)
O1iii—Mg1—O1iv	155.13 (8)	O6—Na1—O3ix	111.84 (7)
O3i—Mg1—O4v	83.70 (5)	O6ix—Na1—O3ix	56.06 (5)
O3ii—Mg1—O4v	170.20 (5)	O6vii—Na1—O3ix	105.27 (6)
O1iii—Mg1—O4v	108.38 (5)	O6x—Na1—O3ix	62.51 (5)
O1iv—Mg1—O4v	89.53 (5)	O3—Na1—O3ix	71.02 (6)
O3i—Mg1—O4	170.20 (5)	O6—Na1—O1xi	118.48 (6)
O3ii—Mg1—O4	83.70 (5)	O6ix—Na1—O1xi	74.30 (5)
O1iii—Mg1—O4	89.53 (5)	O6vii—Na1—O1xi	84.97 (5)
O1iv—Mg1—O4	108.38 (5)	O6x—Na1—O1xi	107.88 (6)
O4v—Mg1—O4	89.05 (7)	O3—Na1—O1xi	146.62 (4)
O6—Mg2—O3iii	85.88 (5)	O3ix—Na1—O1xi	129.17 (3)
O6—Mg2—O2	88.80 (5)	O6—Na1—O1viii	74.30 (5)
O3iii—Mg2—O2	111.03 (6)	O6ix—Na1—O1viii	118.48 (7)
O6—Mg2—O5vi	172.05 (6)	O6vii—Na1—O1viii	107.88 (6)
O3iii—Mg2—O5vi	91.58 (5)	O6x—Na1—O1viii	84.97 (5)
O2—Mg2—O5vi	85.07 (5)	O3—Na1—O1viii	129.17 (3)
O6—Mg2—O5vii	98.45 (5)	O3ix—Na1—O1viii	146.62 (4)
O3iii—Mg2—O5vii	162.38 (6)	O1xi—Na1—O1viii	51.46 (6)
O2—Mg2—O5vii	86.23 (5)	O1v—P1—O1	111.21 (10)
O5vi—Mg2—O5vii	86.22 (5)	O1v—P1—O2v	111.07 (7)
O6—Mg2—O1viii	100.87 (6)	O1—P1—O2v	108.34 (7)
O3iii—Mg2—O1viii	79.79 (5)	O1v—P1—O2	108.34 (7)
O2—Mg2—O1viii	166.18 (6)	O1—P1—O2	111.07 (7)
O5vi—Mg2—O1viii	86.06 (5)	O2v—P1—O2	106.73 (10)
O5vii—Mg2—O1viii	82.62 (5)	O5—P2—O6	111.03 (7)
O6—Na1—O6ix	166.85 (10)	O5—P2—O3	111.42 (7)
O6—Na1—O6vii	86.56 (4)	O6—P2—O3	108.82 (7)
O6ix—Na1—O6vii	91.84 (4)	O5—P2—O4	107.74 (7)
O6—Na1—O6x	91.84 (4)	O6—P2—O4	108.99 (7)
O6ix—Na1—O6x	86.56 (4)	O3—P2—O4	108.78 (7)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O2	0.93	1.57	2.4932 (17)	174