Disordered LiZnVO₄ with a phenacite structure

Single crystals of lithium zinc vanadate, LiZnVO₄, were grown by the flux method. The structural type of this vanadate is characterized by a three-dimensional arrangement of tetra­hedra sharing apices in an LiZnVO₄ network. This arrangement contains three different tetra­hedra, namely one [VO₄] and two disordered mixed-site [Li/ZnO₄] tetra­hedra. The resulting lattice gives rise to hexa­gonal channels running along the [0001] direction. Both sites in the mixed-site [Li/ZnO₄] tetra­hedra are occupied by a statistical mixture of lithium and zinc with a 1:1 ratio. Therefore, LiZnVO₄ appears to be the first vanadate known to crystallize with a disordered phenacite structure. Moreover, the resulting values of calculated bond valences (Li = 1.083, Zn = 2.062 and V = 5.185) tend to confirm the structural model.

Related literature

For related structural studies, see: Hartmann (1989); Capsoni et al. (2006); Zachariasen (1971). For compounds with the same structural type, see: Bu et al. (1996); Elammari & Elouadi (1989); Elouadi & Elammari (1990); Jensen et al. (1998). For bond-valence calculations, see: Brown & Altermatt (1985).

Experimental

Crystal data

• LiZnVO₄

• M_r = 187.25

• Trigonal,

• a = 14.107 (3) Å

• c = 9.441 (2) Å

• V = 1627.1 (6) ų

• Z = 18

• Mo Kα radiation

• μ = 9.06 mm⁻¹

• T = 298 K

• 0.14 × 0.12 × 0.10 mm

Data collection

• Bruker X8 APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Sheldrick, 2003) T_min = 0.292, T_max = 0.404

• 9709 measured reflections

• 1622 independent reflections

• 1213 reflections with I > 2σ(I)

• R_int = 0.070

Refinement

• R[F² > 2σ(F²)] = 0.024

• wR(F²) = 0.055

• S = 1.04

• 1622 reflections

• 69 parameters

• Δρ_max = 0.51 e Å⁻³

• Δρ_min = −0.53 e Å⁻³

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 PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999).

Supporting information

S1. Comment

Our particular interest here is to investigate the form nature of the crystallized phase and determine the structural type that could result from the association of small size cations likely to enter under normal conditions of pressure and temperature, tetrahedral cavities of oxides like in phenacite Be₂SiO₄ network (Hartmann, 1989; Zachariasen, 1971). The compounds currently known to crystallize with such structural type are LiZnPO₄ (Bu et al., 1996; Elammari & Elouadi, 1989; Elouadi & Elammari, 1990) and LiZnAsO₄ (Jensen et al., 1998).

The structural type of the title compound, related to the phenacite structure, could be described (Fig.1) as three dimensional arrangement of [MO₄] tetrahedra ( M= Li/Zn or V) sharing apices. The arrangement concerns three different types of tetrahedra [VO₄] and two disordered sites [Li/ZnO₄] which give rise to an overall disordered phenacite structure. When viewed along the c axis, the packing of [MO₄] tetraherdra results in two types of tunnels: large hexagonal tunnels surrounded by six lozenge like channels (rings of four tetrahedra). Similar description has recently been reported by Capsoni et al. (2006) using a powder x-ray diffraction data of LiZnVO₄. However, a careful observation of the two models can highlights the difference between our two results. Indeed, in addition to the difference of the lengths of chemical bonds, the occupancy rate of cationic Wycoff sites is different. Thus, in our model, there is only a disorder between Li and Zn with a statistical distribution of both ions on the two crystallographic sites, while the third site is only occupied by vanadium cation. Furthermore, A bond-valence analysis (Li <1.083>, Zn<2.062> and <V<5.185>) based on the empirical formula proposed by Brown & Altermatt (1985) is in favor of this model . The cationic disorder mentioned by Capsoni et al. could be seen as due to preparation methods. The powder used was slowly cooled from 853 K after 24 h sintering. Whereas, the growth of our crystal, from a flux melted at 1073 k and slowly cooled with a rate of 5 K h-1. Thus the resulting sintering of our crystal was much longer. A more ordred system is then to be expected.

When such structural type is seen as a close packing of oxygen anions, it appears as a lacunar hexagonal close packing of O^2- ions. Fig.2 shows a typical oxygen layer and the elevation of such oxygen plans as successively stacked ( ABAB···) along [0001]. The coordination sphere of all cations is of tetrahedral type. The analysis of oxygen environment shows a regular triangular cavity for O^2- anions with an average edge length of <V—Li/Zn> = 3.240 Å.

In the case of the present form of LiZnVO₄, the disordered phenacite structure was attributed to the existence of a mixed tetrahedral site [Li/ZnO4] occupied by both Li and Zn. The resulting space group is R-3. LiZnVO₄ is probably the first vanadate known to crystallize with a disordered phenacite structure.

Related literature

For related structural studies, see: Hartmann (1989); Capsoni et al. (2006); Zachariasen (1971). For compounds with the same structural type, see: Bu et al.(1996); Elammari & Elouadi (1989); Elouadi & Elammari (1990); Jensen et al. (1998). For bond-valence calculations, see: Brown & Altermatt (1985).

S2. Experimental

Prior to the crystal growth, pulverulent samples of the compound LiZnVO₄ and the flux LiVO₃ are synthesized by the regular solid state reaction according to the following reactions:

Li₂CO₃ + 2ZnO + V₂O₅ —> 2LiZnVO₄ + CO₂ Li₂CO₃ + V₂O₅ —> 2LiVO₃ + CO₂

Single crystal of the monovanadate LiZnVO₄ were grown from a bath of equimolar mixture of freohly prepared powders of LiZnVO₄ and LiVO₃. The starting mixture was thoroughly ground before to be melted at 1073 K in a platinum crucible and slowly cooled with a rate of 5 K h-1 to 773 K. The furnace was then switched off and the whole system naturally cooled down to room temperature. Single crystal s were collected from the crucible after dissolwing the flux in warmed water.

Computing details

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (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 PLATON (Spek, 2009); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. : A three-dimensional view of LiZnVO4 crystal structure, showing tunnels runnig along the c axis.
	Fig. 2. : Partial projection of the crystal structure on (0 0 1), showing lacunar hexagonal close packing of O^2- ions.

lithium zinc vanadate

Crystal data

LiZnVO4	Dx = 3.440 Mg m^−3
Mr = 187.25	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3	Cell parameters from 9709 reflections
Hall symbol: -R 3	θ = 10–30°
a = 14.107 (3) Å	µ = 9.06 mm^−1
c = 9.441 (2) Å	T = 298 K
V = 1627.1 (6) Å^3	Prism, pale yellow
Z = 18	0.14 × 0.12 × 0.10 mm
F(000) = 1584

Data collection

Bruker X8 APEXII CCD area-detector diffractometer	1622 independent reflections
Radiation source: fine-focus sealed tube	1213 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.070
φ and ω scans	θmax = 35.2°, θmin = 4.0°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −22→22
Tmin = 0.292, Tmax = 0.404	k = −22→22
9709 measured reflections	l = −15→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.024	w = 1/[σ^2(Fo^2) + (0.0124P)^2 + 2.5069P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.055	(Δ/σ)max = 0.001
S = 1.04	Δρmax = 0.51 e Å^−3
1622 reflections	Δρmin = −0.53 e Å^−3
69 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0088 (2)

Special details

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.

Refinement. Refinement on F² for ALL reflections except for 0 with very negative F² or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The observed criterion of F² > σ(F²) is used only for calculating -R-factor-obs 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 (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
V1	0.454581 (17)	0.138171 (16)	0.08352 (2)	0.00790 (7)
Zn1	0.45273 (2)	0.14015 (2)	−0.24915 (3)	0.01132 (7)	0.50
Li1	0.45273 (2)	0.14015 (2)	−0.24915 (3)	0.01132 (7)	0.50
Zn2	0.64622 (2)	0.12175 (3)	0.24882 (3)	0.01150 (7)	0.50
Li2	0.64622 (2)	0.12175 (3)	0.24882 (3)	0.01150 (7)	0.50
O1	0.34102 (7)	0.01142 (7)	0.08427 (11)	0.01335 (17)
O2	0.56475 (8)	0.11882 (9)	0.08215 (10)	0.01353 (17)
O3	0.45578 (8)	0.20780 (8)	−0.06565 (10)	0.01419 (18)
O4	0.45936 (8)	0.20728 (8)	0.23409 (10)	0.01377 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
V1	0.00918 (10)	0.00812 (10)	0.00692 (9)	0.00472 (8)	−0.00012 (6)	−0.00004 (6)
Zn1	0.01190 (12)	0.01217 (13)	0.01038 (12)	0.00637 (10)	0.00052 (9)	0.00069 (9)
Li1	0.01190 (12)	0.01217 (13)	0.01038 (12)	0.00637 (10)	0.00052 (9)	0.00069 (9)
Zn2	0.01159 (13)	0.01368 (13)	0.01016 (12)	0.00701 (10)	0.00005 (9)	0.00037 (9)
Li2	0.01159 (13)	0.01368 (13)	0.01016 (12)	0.00701 (10)	0.00005 (9)	0.00037 (9)
O1	0.0109 (4)	0.0102 (4)	0.0180 (4)	0.0046 (3)	−0.0010 (3)	0.0000 (3)
O2	0.0121 (4)	0.0198 (4)	0.0115 (3)	0.0101 (3)	−0.0005 (3)	−0.0005 (3)
O3	0.0219 (5)	0.0120 (4)	0.0103 (3)	0.0096 (3)	−0.0007 (3)	0.0009 (3)
O4	0.0209 (4)	0.0125 (4)	0.0104 (4)	0.0102 (4)	0.0003 (3)	−0.0004 (3)

Geometric parameters (Å, º)

V1—O1	1.7027 (10)	Zn2—O2	1.9368 (10)
V1—O4	1.7059 (10)	Zn2—O4^x	1.9495 (10)
V1—O2	1.7071 (10)	Zn2—O4^xi	1.9676 (11)
V1—O3	1.7123 (10)	Zn2—Li1^iv	3.1441 (8)
V1—Li2^i	3.1568 (7)	Zn2—Zn1^iv	3.1441 (8)
V1—Li1^ii	3.1719 (8)	Zn2—Li1^viii	3.2314 (8)
V1—Li2^iii	3.2409 (8)	Zn2—Li2^i	3.2675 (7)
V1—Li1^iv	3.2523 (6)	Zn2—Li2^x	3.2676 (7)
V1—Li2^v	3.2978 (7)	O1—Li2^iii	1.9294 (11)
V1—Li1^vi	3.3232 (7)	O1—Zn2^iii	1.9294 (11)
Zn1—O2^vi	1.9410 (10)	O1—Zn1^ii	1.9442 (11)
Zn1—O1^vii	1.9441 (11)	O1—Li1^ii	1.9442 (11)
Zn1—O3^iv	1.9588 (11)	O2—Li1^iv	1.9411 (10)
Zn1—O3	1.9679 (11)	O2—Zn1^iv	1.9411 (10)
Zn1—Zn2^vi	3.1441 (8)	O3—Li1^vi	1.9587 (11)
Zn1—Li2^vi	3.1441 (8)	O3—Zn1^vi	1.9587 (11)
Zn1—Li2^viii	3.2314 (8)	O4—Li2^i	1.9496 (10)
Zn1—Li1^vi	3.2765 (7)	O4—Zn2^i	1.9496 (10)
Zn1—Li1^iv	3.2766 (7)	O4—Li2^v	1.9676 (11)
Zn2—O1^ix	1.9294 (11)	O4—Zn2^v	1.9676 (11)
O1—V1—O4	110.14 (5)	O2^vi—Zn1—O3	115.71 (4)
O1—V1—O2	106.61 (5)	O1^vii—Zn1—O3	106.57 (4)
O4—V1—O2	108.58 (5)	O3^iv—Zn1—O3	110.08 (5)
O1—V1—O3	109.88 (5)	O1^ix—Zn2—O2	111.98 (5)
O4—V1—O3	111.80 (5)	O1^ix—Zn2—O4^x	108.76 (4)
O2—V1—O3	109.69 (5)	O2—Zn2—O4^x	117.26 (4)
O2^vi—Zn1—O1^vii	109.39 (5)	O1^ix—Zn2—O4^xi	102.55 (4)
O2^vi—Zn1—O3^iv	106.12 (4)	O2—Zn2—O4^xi	107.30 (4)
O1^vii—Zn1—O3^iv	108.84 (4)	O4^x—Zn2—O4^xi	107.87 (5)

Symmetry codes: (i) y+1/3, −x+y+2/3, −z+2/3; (ii) −x+y+2/3, −x+1/3, z+1/3; (iii) x−y−1/3, x−2/3, −z+1/3; (iv) x−y+1/3, x−1/3, −z−1/3; (v) −x+y+1, −x+1, z; (vi) y+1/3, −x+y+2/3, −z−1/3; (vii) −y+1/3, x−y−1/3, z−1/3; (viii) −x+1, −y, −z; (ix) y+2/3, −x+y+1/3, −z+1/3; (x) x−y+1/3, x−1/3, −z+2/3; (xi) −y+1, x−y, z.