Crystal structure of magnesium copper(II) bis-[orthophosphate(V)] monohydrate.

Single crystals of magnesium copper(II) bis-[orthophosphate(V)] monohydrate, Mg1.65Cu1.35(PO4)2·H2O, were grown under hydro-thermal conditions. The crystal structure is formed by three types of cationic sites and by two unique (PO4)(3-) anions. One site is occupied by Cu(2+), the second site by Mg(2+)and the third site by a mixture of the two cations with an Mg(2+):Cu(2+) occupancy ratio of 0.657 (3):0.343 (3). The structure is built up from more or less distorted [MgO6] and [(Mg/Cu)O5(H2O)] octa-hedra, [CuO5] square-pyramids and regular PO4 tetra-hedra, leading to a framework structure. Within this framework, two types of layers parallel to (-101) can be distinguished. The first layer is formed by [Cu2O8] dimers linked to PO4 tetra-hedra via common edges. The second, more corrugated layer results from the linkage between [(Cu/Mg)2O8(H2O)2] dimers and [MgO6] octa-hedra by common edges. The PO4 units link the two types of layers, leaving space for channels parallel [101], into which the H atoms of the water mol-ecules protrude. The latter are involved in O-H⋯O hydrogen-bonding inter-actions (one bifurcated) with framework O atoms across the channels.

Chemical context

Transition metal phosphates are an important class of mat­erials characterized by a great structural diversity originating from the presence of different coordination polyhedra MO (with n = 4, 5 and 6) or the possibility of phosphate groups to condense. The alternation of PO4 tetra­hedra and MO polyhedra can give rise to different anionic frameworks [M IIPO4]− with pores or channels offering suitable environments to accommodate different other cations (Gao & Gao, 2005 ▸; Viter & Nagornyi, 2009 ▸). In previous studies, our focus of research was dedicated to the examination of mixed divalent orthophosphates with general formula (M,M′)3(PO4)2·nH2O. For instance, we have succeeded in the preparation and structure determination of some new phosphates such as Ni2Sr(PO4)2·2H2O (Assani et al., 2010a ▸).

In the context of our main research, we report here the hydro­thermal synthesis and structural characterization of the mixed-metal orthophosphate Mg1.65Cu1.35(PO4)2·H2O, isolated during investigation of the qu­inter­nary system Ag2O/MgO/CuO/P2O5/H2O. The title compound crystallizes in the Fe3(PO4)2·H2O structure type (Moore & Araki, 1975 ▸) and is isotypic with other phases of the type (M,M’)3(PO4)2·H2O (Liao et al., 1995 ▸), viz. Co2.59Zn0.41(PO4)2·H2O (Sørensen et al., 2005 ▸), Co2.39Cu0.61(PO4)2·H2O (Assani et al., 2010b ▸), (Cu1−Co)3(PO4)2·H2O (0 < x < 0.20 and 0.55 < x < 0.65), and (Cu1−Zn)3(PO4)2·H2O (0 < x < 0.19) (Viter & Nagornyi, 2006 ▸).

Structural commentary

The principal building units of the crystal structure of the title compound are represented in Fig. 1 ▸. The metal cations are located in three crystallographically independent sites, one octa­hedrally surrounded site entirely occupied by Mg2+, one site with a square-pyramidal coordination completely occupied by Cu2+ and one mixed-occupied (Mg2+/Cu2+) site with an octa­hedral coordination. The [Cu1O5] square pyramid is distorted, with Cu—O bond lengths ranging from 1.9073 (17) to 2.2782 (16) Å. Two [Cu1O5] polyhedra are linked together by edge-sharing to build up a [Cu2O8] dimer. By sharing corners with PO4 tetra­hedra, a layered arrangement parallel to (01) is formed (Fig. 2 ▸). The mixed-occupied [(Mg/Cu)O5(H2O)] octa­hedron is likewise distorted, with (Mg/Cu)—O distances varying between 2.0038 (18) and 2.384 (2) Å. Two [(Mg/Cu)O5(H2O)] octa­hedra share a common edge to built up another dimer [(Mg/Cu)2O8(H2O)2] that links [MgO6] octa­hedra and PO4 tetra­hedra via common vertices to build the second type of layer lying parallel to the first (Fig. 2 ▸). Adjacent layers are connected into a three-dimensional framework by common edges and vertices, and delimit channels parallel to [101], into which the hydrogen atoms of the water mol­ecules protrude. O—H⋯O hydrogen-bonding inter­actions between the water mol­ecules and framework O atoms are present (Table 1 ▸, Fig. 2 ▸).

Figure 1

The principal building units in the crystal structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: x − , −y + , z − ; (ii) −x + 1, −y + 1, −z + 1; (iii) −x + 2, −y + 1, −z + 1; (iv) x + , −y + , z + ; (v) −x + , y + , −z + ; (vi) −x + 2, −y + 1, −z + 2; (vii) −x + , y + , −z + ; (viii) −x + 2, −y + 2, −z + 1.]

Figure 2

A polyhedral view of the title compound, showing the three-dimensional framework structure and O—H⋯O hydrogen bonding (dashed lines) in the channels.

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
O9H9AO1i	0.86	2.22	2.867(2)	132
O9H9AO6ii	0.86	2.38	2.934(2)	123
O9H9BO8iii	0.86	1.93	2.778(2)	170

Symmetry codes: (i) ; (ii) ; (iii) .

Synthesis and crystallization

The title compound, Mg1.65Cu1.35(PO4)2·H2O, was synthesized hydro­thermally form a reaction mixture of AgNO3, MgO, metallic copper, and 85wt% phospho­ric acid in the molar ratio Ag: Mg: Cu: P = 1: 4: 4.5: 6 in 12.5 ml of water. The hydro­thermal reaction was conducted in a 23 ml Teflon-lined autoclave under autogenous pressure at 493 K for three days. The resulting product was filtered off, washed with deionized water and dried in air. The obtained blue crystals correspond to the title compound.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. The M2 site features mixed occupation by Mg2+ and Cu2+ whereas the other two cationic sites do not show any significant disorder. Refinement of the occupancy of M2 resulted in a ratio of Mg2+:Cu2+ = 0.657 (3):0.343 (3). The O-bound H atoms were initially located in a difference map and refined with O—H distance restraints of 0.83 (5). In the last refinement cycle, the distances were fixed at 0.86 Å and the H atoms refined in the riding-model approximation with U iso(H) set to 1.5U eq(O). The highest remaining positive and negative electron densities observed in the final Fourier map are at 0.81 Å and 0.43 Å, respectively, from Cu1.

Table 2

Experimental details

Crystal data
Chemical formula	Mg1.65Cu1.35(PO4)2H2O
M r	333.65
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	296
a, b, c ()	8.0701(1), 9.8661(2), 8.9944(2)
()	115.242(1)
V (3)	647.76(2)
Z	4
Radiation type	Mo K
(mm1)	5.16
Crystal size (mm)	0.31 0.27 0.18
Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Bruker, 2009 ▸)
T min, T max	0.574, 0.748
No. of measured, independent and observed [I > 2(I)] reflections	9233, 1673, 1617
R int	0.025
(sin /)max (1)	0.676
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.020, 0.058, 1.24
No. of reflections	1673
No. of parameters	129
H-atom treatment	H-atom parameters constrained
max, min (e 3)	0.55, 0.34

Computer programs: APEX2 and SAINT (Bruker, 2009 ▸), SHELXS97 and SHELXL97 (Sheldrick, 2008 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989014026930/wm5097sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989014026930/wm5097Isup2.hkl

CCDC reference: 1038224

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

Mg1.65Cu1.35(PO4)2·H2O	F(000) = 651
Mr = 333.65	Dx = 3.421 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -p 2yn	Cell parameters from 1673 reflections
a = 8.0701 (1) Å	θ = 2.9–28.7°
b = 9.8661 (2) Å	µ = 5.16 mm−1
c = 8.9944 (2) Å	T = 296 K
β = 115.242 (1)°	Prism, blue
V = 647.76 (2) Å3	0.31 × 0.27 × 0.18 mm
Z = 4

Bruker X8 APEX diffractometer	1673 independent reflections
Radiation source: fine-focus sealed tube	1617 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
φ and ω scans	θmax = 28.7°, θmin = 2.9°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −10→10
Tmin = 0.574, Tmax = 0.748	k = −11→13
9233 measured reflections	l = −12→12

Refinement on F2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.020	H-atom parameters constrained
wR(F2) = 0.058	w = 1/[σ2(Fo2) + (0.0209P)2 + 1.2623P] where P = (Fo2 + 2Fc2)/3
S = 1.24	(Δ/σ)max = 0.001
1673 reflections	Δρmax = 0.55 e Å−3
129 parameters	Δρmin = −0.34 e Å−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0022 (6)

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 > 2σ(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.

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cu1	0.64417 (4)	0.37312 (3)	0.56030 (3)	0.00781 (10)
Mg1	0.98357 (10)	0.62883 (7)	0.72316 (9)	0.00506 (16)
Cu2	0.88601 (7)	0.86606 (5)	0.46685 (6)	0.00771 (19)	0.343 (3)
Mg2	0.88601 (7)	0.86606 (5)	0.46685 (6)	0.00771 (19)	0.657 (3)
P1	0.70807 (7)	0.57775 (6)	0.32947 (7)	0.00456 (13)
P2	0.88138 (7)	0.33721 (6)	0.86197 (7)	0.00517 (13)
O1	0.5825 (2)	0.51553 (17)	0.4023 (2)	0.0088 (3)
O4	0.8713 (2)	0.64903 (17)	0.4655 (2)	0.0092 (3)
O3	0.5882 (2)	0.68080 (16)	0.19945 (19)	0.0068 (3)
O2	0.7722 (2)	0.46440 (16)	0.2486 (2)	0.0071 (3)
O5	0.8579 (2)	0.36647 (17)	1.0187 (2)	0.0088 (3)
O6	0.7227 (2)	0.24356 (17)	0.7487 (2)	0.0081 (3)
O7	0.8521 (2)	0.46259 (17)	0.75021 (19)	0.0078 (3)
O8	1.0684 (2)	0.27408 (17)	0.9037 (2)	0.0094 (3)
O9	1.1046 (2)	0.9118 (2)	0.4255 (2)	0.0139 (4)
H9A	1.0944	0.9060	0.3265	0.021*
H9B	1.2106	0.8782	0.4857	0.021*

	U11	U22	U33	U12	U13	U23
Cu1	0.01066 (15)	0.00588 (15)	0.00473 (15)	−0.00143 (9)	0.00122 (11)	0.00069 (9)
Mg1	0.0054 (3)	0.0042 (3)	0.0049 (3)	−0.0001 (2)	0.0016 (3)	0.0003 (3)
Cu2	0.0060 (3)	0.0097 (3)	0.0068 (3)	0.00074 (16)	0.00216 (19)	0.00187 (17)
Mg2	0.0060 (3)	0.0097 (3)	0.0068 (3)	0.00074 (16)	0.00216 (19)	0.00187 (17)
P1	0.0056 (2)	0.0043 (3)	0.0034 (2)	0.00024 (18)	0.00156 (19)	−0.00019 (18)
P2	0.0064 (2)	0.0046 (2)	0.0041 (2)	−0.00022 (19)	0.00177 (19)	0.00026 (19)
O1	0.0092 (7)	0.0097 (8)	0.0091 (7)	0.0016 (6)	0.0054 (6)	0.0036 (6)
O4	0.0084 (7)	0.0097 (8)	0.0062 (7)	−0.0017 (6)	−0.0001 (6)	−0.0025 (6)
O3	0.0088 (7)	0.0052 (7)	0.0050 (7)	0.0016 (6)	0.0017 (6)	0.0011 (6)
O2	0.0084 (7)	0.0061 (7)	0.0064 (7)	0.0022 (6)	0.0027 (6)	−0.0014 (6)
O5	0.0111 (8)	0.0102 (8)	0.0053 (7)	−0.0004 (6)	0.0036 (6)	−0.0014 (6)
O6	0.0091 (7)	0.0078 (7)	0.0060 (7)	−0.0027 (6)	0.0019 (6)	0.0005 (6)
O7	0.0083 (7)	0.0056 (7)	0.0071 (7)	−0.0014 (6)	0.0011 (6)	0.0021 (6)
O8	0.0086 (7)	0.0099 (8)	0.0094 (8)	0.0025 (6)	0.0035 (6)	0.0030 (6)
O9	0.0085 (7)	0.0256 (10)	0.0073 (8)	0.0035 (7)	0.0032 (6)	0.0045 (7)

Cu1—O1	1.9073 (17)	Cu2—O3iv	2.0837 (16)
Cu1—O8i	1.9322 (17)	Cu2—O4	2.1442 (18)
Cu1—O6	1.9980 (16)	Cu2—O9viii	2.384 (2)
Cu1—O7	2.0169 (16)	P1—O4	1.5340 (17)
Cu1—O1ii	2.2782 (16)	P1—O2	1.5392 (16)
Mg1—O7	2.0236 (18)	P1—O3	1.5401 (16)
Mg1—O2iii	2.0898 (17)	P1—O1	1.5491 (17)
Mg1—O4	2.1070 (18)	P2—O8	1.5241 (17)
Mg1—O3iv	2.1071 (17)	P2—O5	1.5279 (17)
Mg1—O6v	2.1156 (17)	P2—O7	1.5473 (17)
Mg1—O5vi	2.1205 (18)	P2—O6	1.5550 (17)
Cu2—O9	2.0038 (18)	O9—H9A	0.8600
Cu2—O5v	2.0268 (17)	O9—H9B	0.8600
Cu2—O2vii	2.0535 (17)
O1—Cu1—O8i	96.29 (7)	O5v—Cu2—O2vii	80.18 (7)
O1—Cu1—O6	172.25 (7)	O9—Cu2—O3iv	82.06 (7)
O8i—Cu1—O6	91.43 (7)	O5v—Cu2—O3iv	107.59 (7)
O1—Cu1—O7	99.62 (7)	O2vii—Cu2—O3iv	163.32 (7)
O8i—Cu1—O7	146.81 (7)	O9—Cu2—O4	105.96 (8)
O6—Cu1—O7	73.33 (7)	O5v—Cu2—O4	87.11 (7)
O1—Cu1—O1ii	77.52 (7)	O2vii—Cu2—O4	117.13 (7)
O8i—Cu1—O1ii	116.46 (6)	O3iv—Cu2—O4	78.56 (6)
O6—Cu1—O1ii	99.65 (6)	O9—Cu2—O9viii	89.45 (7)
O7—Cu1—O1ii	95.41 (6)	O5v—Cu2—O9viii	80.53 (6)
O7—Mg1—O2iii	98.29 (7)	O2vii—Cu2—O9viii	81.28 (6)
O7—Mg1—O4	101.96 (7)	O3iv—Cu2—O9viii	85.44 (6)
O2iii—Mg1—O4	96.67 (7)	O4—Cu2—O9viii	155.82 (7)
O7—Mg1—O3iv	171.09 (8)	O4—P1—O2	111.26 (9)
O2iii—Mg1—O3iv	90.39 (7)	O4—P1—O3	110.54 (9)
O4—Mg1—O3iv	78.89 (7)	O2—P1—O3	110.47 (9)
O7—Mg1—O6v	86.54 (7)	O4—P1—O1	109.79 (9)
O2iii—Mg1—O6v	166.01 (7)	O2—P1—O1	108.93 (9)
O4—Mg1—O6v	95.14 (7)	O3—P1—O1	105.69 (9)
O3iv—Mg1—O6v	84.55 (7)	O8—P2—O5	110.47 (9)
O7—Mg1—O5vi	89.35 (7)	O8—P2—O7	110.33 (9)
O2iii—Mg1—O5vi	77.24 (7)	O5—P2—O7	113.81 (9)
O4—Mg1—O5vi	167.90 (8)	O8—P2—O6	111.75 (10)
O3iv—Mg1—O5vi	90.60 (7)	O5—P2—O6	108.96 (9)
O6v—Mg1—O5vi	89.76 (7)	O7—P2—O6	101.22 (9)
O9—Cu2—O5v	165.32 (8)	H9A—O9—H9B	104.9
O9—Cu2—O2vii	87.74 (7)

D—H···A	D—H	H···A	D···A	D—H···A
O9—H9A···O1vii	0.86	2.22	2.867 (2)	132
O9—H9A···O6iii	0.86	2.38	2.934 (2)	123
O9—H9B···O8ix	0.86	1.93	2.778 (2)	170