Crystal structure of disilver(I) dizinc(II) iron(III) tris-(orthovanadate) with an alluaudite-type structure.

The title compound, Ag2Zn2Fe(VO4)3, has been synthesized by solid-state reactions and belongs to the alluaudite structure family. In the crystal structure, four sites are positioned at special positions. One silver site is located on an inversion centre (Wyckoff position 4b), and an additional silver site, as well as one zinc and one vanadium site, on twofold rotation axes (4e). One site on a general position is statistically occupied by FeIII and ZnII cations that are octa-hedrally surrounded by O atoms. The three-dimensional framework structure of the title vanadate results from [(Zn,Fe)2O10] units of edge-sharing [(Zn,Fe)O6] octa-hedra that alternate with [ZnO6] octa-hedra so as to form infinite chains parallel to [10]. These chains are linked through VO4 tetra-hedra by sharing vertices, giving rise to layers extending parallel to (010). Such layers are shared by common vanadate tetra-hedra. The resulting three-dimensional framework delimits two types of channels parallel to [001] in which the silver sites are located with four- and sixfold coordination by oxygen.

Chemical context

The crystal structure of the mineral alluaudite with general formula A(1)A(2)M(1)M(2)2(XO4)3 was determined nearly fifty years ago by Moore (1971 ▸). In the structure, the two A sites can be occupied by mono- or divalent cations of medium size, and the M(1) and M(2) sites can accommodate di- or trivalent cations, which are generally transition metals and are octa­hedrally surrounded. The specific feature of the alluaudite structure is the existence of two channels parallel to [001] in which the A-site cations are located. As a result, alluaudite-type compounds can exhibit electronic and/or ionic conductivity (Hatert, 2008 ▸). In addition, alluaudite-type compounds have been reported as materials for fossil energy conversion, as sensor materials and storage energy materials (Korzenski et al., 1998 ▸), and as materials used in catalysis (Kacimi et al., 2005 ▸).

Accordingly, the synthesis and structural characterization of new alluaudite-type phosphates and vanadates within pseudo-ternary A 2O/MO/P2O5 or pseudo-quaternary A 2O/MO/Fe2O3/P2O5 systems using hydro­thermal or solid-state reactions was the focus of our current research. Obtained phases are, for example, NaMg3(HPO4)2(PO4) (Ould Saleck et al., 2015 ▸), Na2Co2Fe(PO4)3 (Bouraima et al., 2015 ▸) or Na1.67Zn1.67Fe1.33(PO4)3 (Khmiyas et al., 2015 ▸). We have also succeeded in preparing the first vanadate-based alluaudite-type phase (Na0.70)(Na0.70,Mn0.30)(FeIII,FeII)2FeII(VO4)3 (Benhsina et al., 2016 ▸). A second alluaudite-type vanadate with composition Na2(FeIII/CoII)2CoII(VO4)3 was prepared by Hadouchi et al. (2016 ▸) shortly afterwards.

In this context, the current exploration of A 2O/MO/Fe2O3/V2O5 systems, where A is a monovalent cation and M a divalent cation, led to another vandanate with alluaudite-type structure, namely Ag2Zn2Fe(VO4)3. Its synthesis and crystal structure are reported in this article.

Structural commentary

The principal building units of the crystal structure of the new member of the alluaudite-type family are represented in Fig. 1 ▸. All atoms are in general positions except for four atoms that are located on special positions. Ag1 is located on an inversion centre (Wyckoff position 4b), and Ag2 as well as Zn2 and V2 are located on twofold rotation axes (4e) of space group C2/c. The M2 site is in a general position (8f) and statistically occupied by Fe1 and Zn1 atoms that are octa­hedrally surrounded by O atoms. Such a partial cationic disorder was also reported for the cobalt homologue Na2(FeIII/CoII)2CoII(VO4)3 (Hadouchi et al., 2016 ▸).

Figure 1

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

The crystal structure of Ag2Zn2Fe(VO4)3 is made up from [(Zn,Fe)12O10] dimers, resulting from edge-sharing [(Zn,Fe)1O6] octa­hedra, that are connected by a common edge to [Zn2O6] octa­hedra. The linkage of alternating [(Zn,Fe)12O10] and [Zn2O6] units leads to infinite zigzag chains along [10] (Fig. 2 ▸). These chains are linked via the vertices of VO4 tetra­hedra into layers parallel to (010), as shown in Fig. 3 ▸. Adjacent layers are linked by V1O4 tetra­hedra into a three-dimensional framework structure that delimits two types of channels in which the AgI cations reside (Fig. 4 ▸). The Ag1 site is located in one channel and is surrounded by four oxygen atoms, whereas the Ag2 site in the second channel is surrounded by six oxygen atoms.

Figure 2

Edge-sharing [(Zn,Fe)1O6] and [Zn2O6] octa­hedra forming a kinked chain running parallel to [10].

Figure 3

A layer perpendicular to (010), resulting from the connection of chains via the vertices of VO4 tetra­hedra and [ZnO6] octa­hedra.

Figure 4

Polyhedral representation of Ag2Zn2Fe(VO4)3 showing the channels running parallel to the [001] direction.

The calculated bond-valences sums (Brown & Altermatt, 1985 ▸) of the atoms in the structure are in the expected ranges for AgI, ZnII, FeIII and VV and are as follows (values in valence units): Ag1 (0.83), Ag2 (1.11), Zn1 (1.95), Zn2 (2.20), Fe1 (2.67), V1 (4.98) and V2 (4.93); values of oxygen atoms range between 1.90 and 2.01 valence units.

Database Survey

Over the last twenty years, many synthetic alluaudite-type phosphates, arsenates, sulfates and molybdates have been reported, such as NaMnFe2(PO4)3 used as the positive electrode in sodium and lithium batteries (Trad et al., 2010 ▸; Kim et al., 2014 ▸; Huang et al., 2015 ▸), Na2.44Mn1.79(SO4)3 used as a potential high-voltage cathode material (ca 4.4 V) for sodium batteries (Dwibedi et al., 2015 ▸), K0.13Na3.87Mg(MoO4)3 as a promising compound for developing new materials with high ionic conductivity (Ennajeh et al., 2015 ▸), or NaZn3(AsO4)(AsO3OH)2 (Đorđević et al., 2015 ▸).

Synthesis and crystallization

Ag2Zn2Fe(VO4)3 was prepared by a solid-state reaction. A stoichiometric amount of silver nitrate (AgNO3), zinc acetate (Zn(CH3COO)2·2H2O), iron nitrate (Fe(NO3)3)·9H2O) and vanadium oxide (V2O5) was employed in the molar ratio Ag: Zn:Fe:V = 2:2:1:3 and put into a platinum cruicible. After different heat treatments at lower temperatures to remove water and other voliatile gaseous products, the reaction mixture was melted at 1033 K for 30 minutes, followed by slow cooling with a 5 K h−1 rate to room temperature. The resulting product contained parallelepipedic orange crystals corres­ponding to the studied title vanadate. In addition, small block-like crystals with poor quality and unidentified by X-ray powder diffraction were present.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1 ▸. The remaining maximum and minimum electron density peaks in the final Fourier map are 0.40 Å away from Fe1 and 0.62 Å from Ag1, respectively. Due to charge neutrality, sites Zn1 and Fe2 were modelled as statistically occupied, assuming a trivalent oxidation state for the iron site.

Table 1

Experimental details

Crystal data
Chemical formula	Ag2Zn2Fe(VO4)3
M r	747.15
Crystal system, space group	Monoclinic, C2/c
Temperature (K)	296
a, b, c (Å)	11.8025 (2), 12.9133 (2), 6.8000 (1)
β (°)	110.759 (1)
V (Å3)	969.10 (3)
Z	4
Radiation type	Mo Kα
μ (mm−1)	13.09
Crystal size (mm)	0.31 × 0.26 × 0.20
Data collection
Diffractometer	Bruker X8 APEX
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 ▸)
T min, T max	0.596, 0.748
No. of measured, independent and observed [I > 2σ(I)] reflections	30791, 2662, 2437
R int	0.042
(sin θ/λ)max (Å−1)	0.869
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.021, 0.048, 1.13
No. of reflections	2662
No. of parameters	95
Δρmax, Δρmin (e Å−3)	1.36, −2.41

Computer programs: APEX2 and SAINT (Bruker, 2014 ▸), SHELXT2014 (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸), DIAMOND (Brandenburg, 2006 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S205698901801071X/wm5454sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901801071X/wm5454Isup2.hkl

CCDC reference: 1857879

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

Ag2Zn2Fe(VO4)3	F(000) = 1380
Mr = 747.15	Dx = 5.121 Mg m−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.8025 (2) Å	Cell parameters from 2662 reflections
b = 12.9133 (2) Å	θ = 2.4–38.1°
c = 6.8000 (1) Å	µ = 13.09 mm−1
β = 110.759 (1)°	T = 296 K
V = 969.10 (3) Å3	Parallelepiped, orange
Z = 4	0.31 × 0.26 × 0.20 mm

Bruker X8 APEX diffractometer	2662 independent reflections
Radiation source: fine-focus sealed tube	2437 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.042
φ and ω scans	θmax = 38.1°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	h = −18→20
Tmin = 0.596, Tmax = 0.748	k = −22→22
30791 measured reflections	l = −11→9

Refinement on F2	0 restraints
Least-squares matrix: full	w = 1/[σ2(Fo2) + (0.0126P)2 + 4.2342P] where P = (Fo2 + 2Fc2)/3
R[F2 > 2σ(F2)] = 0.021	(Δ/σ)max = 0.001
wR(F2) = 0.048	Δρmax = 1.36 e Å−3
S = 1.13	Δρmin = −2.41 e Å−3
2662 reflections	Extinction correction: SHELXL2016 (Sheldrick, 2015b), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
95 parameters	Extinction coefficient: 0.00163 (6)

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ag1	0.500000	0.49090 (3)	0.750000	0.02736 (7)
Ag2	0.500000	0.000000	0.500000	0.02115 (6)
Zn2	0.500000	0.23529 (2)	0.250000	0.00945 (6)
Zn1	0.29222 (2)	0.34062 (2)	0.38041 (3)	0.00652 (5)	0.5
Fe1	0.29222 (2)	0.34062 (2)	0.38041 (3)	0.00652 (5)	0.5
V1	0.27045 (3)	0.38683 (2)	0.88206 (4)	0.00612 (5)
V2	0.500000	0.20643 (3)	0.750000	0.00602 (6)
O1	0.12116 (12)	0.39616 (11)	0.8338 (2)	0.0128 (2)
O2	0.28524 (13)	0.31700 (11)	0.6746 (2)	0.0124 (2)
O3	0.33803 (14)	0.50767 (11)	0.8997 (2)	0.0139 (2)
O4	0.33926 (12)	0.32576 (11)	1.1233 (2)	0.0112 (2)
O5	0.46319 (12)	0.27705 (11)	0.5152 (2)	0.0099 (2)
O6	0.38484 (12)	0.12416 (10)	0.7343 (2)	0.0115 (2)

	U11	U22	U33	U12	U13	U23
Ag1	0.01209 (9)	0.05204 (18)	0.01674 (11)	0.000	0.00362 (8)	0.000
Ag2	0.03519 (13)	0.01557 (9)	0.01224 (9)	−0.01110 (8)	0.00786 (9)	−0.00296 (7)
Zn2	0.00905 (11)	0.01104 (12)	0.00942 (12)	0.000	0.00472 (9)	0.000
Zn1	0.00607 (8)	0.00863 (9)	0.00535 (9)	0.00074 (6)	0.00264 (6)	0.00062 (6)
Fe1	0.00607 (8)	0.00863 (9)	0.00535 (9)	0.00074 (6)	0.00264 (6)	0.00062 (6)
V1	0.00655 (10)	0.00709 (10)	0.00474 (10)	0.00040 (8)	0.00202 (8)	0.00021 (8)
V2	0.00649 (14)	0.00644 (14)	0.00448 (14)	0.000	0.00112 (11)	0.000
O1	0.0095 (5)	0.0130 (5)	0.0160 (6)	0.0017 (4)	0.0045 (5)	0.0008 (5)
O2	0.0140 (6)	0.0155 (6)	0.0082 (5)	0.0017 (5)	0.0046 (4)	−0.0004 (4)
O3	0.0149 (6)	0.0116 (5)	0.0158 (6)	−0.0010 (4)	0.0061 (5)	0.0017 (5)
O4	0.0123 (5)	0.0133 (5)	0.0078 (5)	0.0037 (4)	0.0034 (4)	0.0019 (4)
O5	0.0090 (5)	0.0135 (5)	0.0075 (5)	0.0019 (4)	0.0035 (4)	0.0027 (4)
O6	0.0087 (5)	0.0103 (5)	0.0136 (6)	−0.0007 (4)	0.0019 (4)	0.0016 (4)

Ag1—O3i	2.4699 (15)	Zn2—O1v	2.1619 (15)
Ag1—O3ii	2.4699 (16)	Zn1—O6viii	2.0068 (14)
Ag1—O3iii	2.4734 (16)	Zn1—O4x	2.0222 (14)
Ag1—O3	2.4734 (16)	Zn1—O3i	2.0241 (15)
Ag2—O6iv	2.4374 (14)	Zn1—O2	2.0540 (14)
Ag2—O6iii	2.4374 (14)	Zn1—O5	2.0675 (13)
Ag2—O1v	2.5032 (15)	Zn1—O2viii	2.2082 (15)
Ag2—O1vi	2.5032 (15)	V1—O1	1.6784 (14)
Ag2—O1vii	2.5873 (14)	V1—O2	1.7343 (14)
Ag2—O1viii	2.5873 (14)	V1—O3	1.7372 (15)
Zn2—O5ix	2.0704 (14)	V1—O4	1.7402 (13)
Zn2—O5	2.0705 (14)	V2—O6	1.6984 (14)
Zn2—O4iii	2.1325 (13)	V2—O6iii	1.6984 (14)
Zn2—O4x	2.1325 (13)	V2—O5iii	1.7544 (13)
Zn2—O1viii	2.1619 (15)	V2—O5	1.7544 (13)
O3i—Ag1—O3ii	179.15 (7)	O5—Zn2—O1v	107.36 (5)
O3i—Ag1—O3iii	92.83 (5)	O4iii—Zn2—O1v	85.01 (5)
O3ii—Ag1—O3iii	87.10 (5)	O4x—Zn2—O1v	161.31 (5)
O3i—Ag1—O3	87.10 (5)	O1viii—Zn2—O1v	76.52 (7)
O3ii—Ag1—O3	92.83 (5)	O6viii—Zn1—O4x	104.63 (6)
O3iii—Ag1—O3	169.95 (7)	O6viii—Zn1—O3i	91.33 (6)
O6iv—Ag2—O6iii	180.00 (6)	O4x—Zn1—O3i	89.94 (6)
O6iv—Ag2—O1v	105.99 (5)	O6viii—Zn1—O2	90.95 (6)
O6iii—Ag2—O1v	74.01 (5)	O4x—Zn1—O2	161.09 (6)
O6iv—Ag2—O1vi	74.01 (5)	O3i—Zn1—O2	100.52 (6)
O6iii—Ag2—O1vi	105.99 (5)	O6viii—Zn1—O5	168.70 (6)
O1v—Ag2—O1vi	180.00 (6)	O4x—Zn1—O5	79.73 (5)
O6iv—Ag2—O1vii	107.39 (5)	O3i—Zn1—O5	99.16 (6)
O6iii—Ag2—O1vii	72.61 (5)	O2—Zn1—O5	83.05 (5)
O1v—Ag2—O1vii	116.56 (6)	O6viii—Zn1—O2viii	80.30 (5)
O1vi—Ag2—O1vii	63.44 (6)	O4x—Zn1—O2viii	89.43 (5)
O6iv—Ag2—O1viii	72.61 (5)	O3i—Zn1—O2viii	171.16 (6)
O6iii—Ag2—O1viii	107.39 (5)	O2—Zn1—O2viii	82.59 (6)
O1v—Ag2—O1viii	63.44 (6)	O5—Zn1—O2viii	89.40 (5)
O1vi—Ag2—O1viii	116.56 (6)	O1—V1—O2	106.24 (7)
O1vii—Ag2—O1viii	180.0	O1—V1—O3	111.93 (7)
O5ix—Zn2—O5	149.81 (8)	O2—V1—O3	110.32 (7)
O5ix—Zn2—O4iii	77.17 (5)	O1—V1—O4	108.88 (7)
O5—Zn2—O4iii	86.37 (5)	O2—V1—O4	112.54 (7)
O5ix—Zn2—O4x	86.37 (5)	O3—V1—O4	107.01 (7)
O5—Zn2—O4x	77.17 (5)	O6—V2—O6iii	102.56 (10)
O4iii—Zn2—O4x	113.56 (8)	O6—V2—O5iii	108.46 (7)
O5ix—Zn2—O1viii	107.36 (5)	O6iii—V2—O5iii	109.48 (6)
O5—Zn2—O1viii	96.35 (6)	O6—V2—O5	109.48 (6)
O4iii—Zn2—O1viii	161.31 (5)	O6iii—V2—O5	108.47 (7)
O4x—Zn2—O1viii	85.01 (5)	O5iii—V2—O5	117.36 (9)
O5ix—Zn2—O1v	96.35 (6)