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A single crystal of MoVAlO7, vanadium aluminium molybdate, has been grown. The present structure determination is more precise than a previous powder-pattern investigation [Knorr, Jacubus, Dabrowska & Kurzawa (1998). Eur. J. Solid State Inorg. Chem. 35, 519-530]. A three-dimensional [MoAlO6]3n-n network surrounds infinite strings of [VO]3+ groups [V-O = 1.586 (4) Å] lying in the mirror planes.
Supporting information
MoVAlO7 was prepared by direct interaction of a 2:1:1 stoichiometric mixture
of MoO3, V2O5 and Al2O3 (99.5% Aldrich Chemical Company). The
carefully ground mixture was introduced into an open quartz tube and heated
during for 24 h at 963 K. The density was determined using an Accupyc 1330
Micromeritics pycnometer.
The cell parameters and space group Pnma were clearly established. Since
the cell volume was close to that of the Mo1 + xV2 -
xO8 phase, a rough formula of [Mo3O8] was tried. In the Fourier
and subsequent refinements of the three main electron-density peaks, it
appeared, following the values of the displacement parameters, that one peak
was surely Mo, the second V, and that the remaining one was less populated in
electrons. This last crystallographic site we ascribed to aluminium. The
difference Fourier gave five independent O-atom positions. Refinement of the
positional and anisotropic displacement parameters gave a very good R
factor. The resulting formula was MoVAlO7 with Z = 4 units per cell.
Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXL96 (Sheldrick, 1996); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL96.
vanadium aluminium molybdate
top
Crystal data top
MoVAlO7 | Dx = 3.394 Mg m−3 Dm = 3.38 (2) Mg m−3 Dm measured by helium pycnometry |
Mr = 285.86 | Mo Kα radiation, λ = 0.71073 Å |
Orthorhombic, Pnma | Cell parameters from 3861 reflections |
a = 12.7360 (2) Å | θ = 2–32° |
b = 5.3790 (4) Å | µ = 4.04 mm−1 |
c = 8.1660 (6) Å | T = 293 K |
V = 559.43 (6) Å3 | Parallelepiped, green |
Z = 4 | 0.08 × 0.05 × 0.02 mm |
F(000) = 536 | |
Data collection top
Nonius KappaCCDr diffractometer | 1054 independent reflections |
Radiation source: fine-focus sealed tube | 878 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.067 |
ψ and ω scans | θmax = 32.0°, θmin = 4.1° |
Absorption correction: multi-scan Blessing (1995) | h = −18→18 |
Tmin = 0.842, Tmax = 0.930 | k = −7→7 |
3861 measured reflections | l = −12→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)] = 0.035 | w = 1/[σ2(Fo2) + (0.0488P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.083 | (Δ/σ)max < 0.001 |
S = 1.05 | Δρmax = 1.16 e Å−3 |
1054 reflections | Δρmin = −2.76 e Å−3 |
56 parameters | Extinction correction: SHELXL96, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
0 restraints | Extinction coefficient: 0.0061 (12) |
Crystal data top
MoVAlO7 | V = 559.43 (6) Å3 |
Mr = 285.86 | Z = 4 |
Orthorhombic, Pnma | Mo Kα radiation |
a = 12.7360 (2) Å | µ = 4.04 mm−1 |
b = 5.3790 (4) Å | T = 293 K |
c = 8.1660 (6) Å | 0.08 × 0.05 × 0.02 mm |
Data collection top
Nonius KappaCCDr diffractometer | 1054 independent reflections |
Absorption correction: multi-scan Blessing (1995) | 878 reflections with I > 2σ(I) |
Tmin = 0.842, Tmax = 0.930 | Rint = 0.067 |
3861 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.035 | 56 parameters |
wR(F2) = 0.083 | 0 restraints |
S = 1.05 | Δρmax = 1.16 e Å−3 |
1054 reflections | Δρmin = −2.76 e Å−3 |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
Mo | 0.35545 (3) | 0.7500 | 0.45506 (5) | 0.00617 (14) | |
V | 0.48684 (6) | 0.2500 | 0.06840 (9) | 0.00710 (18) | |
Al | 0.61335 (10) | 0.7500 | 0.26596 (16) | 0.0059 (3) | |
O1 | 0.35102 (19) | 0.4923 (5) | 0.5845 (3) | 0.0151 (5) | |
O2 | 0.4738 (2) | 0.7500 | 0.3457 (4) | 0.0137 (7) | |
O3 | 0.2482 (2) | 0.7500 | 0.3198 (4) | 0.0120 (7) | |
O4 | 0.57056 (17) | 0.5208 (4) | 0.0989 (3) | 0.0092 (4) | |
O5 | 0.4065 (3) | 0.2500 | 0.2167 (4) | 0.0178 (8) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Mo | 0.00412 (18) | 0.0093 (2) | 0.0051 (2) | 0.000 | −0.00044 (12) | 0.000 |
V | 0.0087 (3) | 0.0072 (4) | 0.0054 (4) | 0.000 | −0.0007 (3) | 0.000 |
Al | 0.0050 (5) | 0.0075 (6) | 0.0052 (6) | 0.000 | 0.0005 (5) | 0.000 |
O1 | 0.0179 (12) | 0.0142 (13) | 0.0131 (12) | 0.0009 (9) | −0.0001 (9) | 0.0054 (10) |
O2 | 0.0062 (13) | 0.0188 (17) | 0.0161 (18) | 0.000 | 0.0032 (13) | 0.000 |
O3 | 0.0061 (13) | 0.0183 (17) | 0.0116 (16) | 0.000 | −0.0054 (12) | 0.000 |
O4 | 0.0111 (10) | 0.0087 (10) | 0.0079 (10) | −0.0004 (8) | −0.0038 (8) | 0.0000 (8) |
O5 | 0.0204 (17) | 0.0174 (18) | 0.0155 (19) | 0.000 | 0.0067 (14) | 0.000 |
Geometric parameters (Å, º) top
Mo—O1 | 1.744 (3) | V—Vv | 2.9315 (6) |
Mo—O1i | 1.744 (3) | V—Viv | 2.9315 (6) |
Mo—O2 | 1.752 (3) | V—Aliv | 3.0138 (15) |
Mo—O3 | 1.757 (3) | Al—O1vi | 1.843 (3) |
V—O5 | 1.586 (4) | Al—O1vii | 1.843 (3) |
V—O4ii | 1.822 (2) | Al—O3viii | 1.855 (3) |
V—O4 | 1.822 (2) | Al—O2 | 1.893 (3) |
V—O4iii | 1.980 (2) | Al—O4i | 1.918 (2) |
V—O4iv | 1.980 (2) | Al—O4 | 1.918 (2) |
| | | |
O1—Mo—O1i | 105.29 (19) | O1vi—Al—O1vii | 90.00 (18) |
O1—Mo—O2 | 109.67 (10) | O1vi—Al—O3viii | 91.27 (12) |
O1i—Mo—O2 | 109.67 (10) | O1vii—Al—O3viii | 91.27 (12) |
O1—Mo—O3 | 110.85 (10) | O1vi—Al—O2 | 90.18 (12) |
O1i—Mo—O3 | 110.85 (10) | O1vii—Al—O2 | 90.18 (12) |
O2—Mo—O3 | 110.39 (16) | O3viii—Al—O2 | 177.96 (16) |
O5—V—O4ii | 105.85 (11) | O1vi—Al—O4i | 94.98 (11) |
O5—V—O4 | 105.85 (11) | O1vii—Al—O4i | 174.91 (12) |
O4ii—V—O4 | 106.13 (14) | O3viii—Al—O4i | 89.70 (11) |
O5—V—O4iii | 106.78 (13) | O2—Al—O4i | 88.74 (12) |
O4ii—V—O4iii | 79.20 (10) | O1vi—Al—O4 | 174.90 (11) |
O4—V—O4iii | 143.91 (6) | O1vii—Al—O4 | 94.98 (11) |
O5—V—O4iv | 106.78 (13) | O3viii—Al—O4 | 89.70 (11) |
O4ii—V—O4iv | 143.91 (6) | O2—Al—O4 | 88.74 (12) |
O4—V—O4iv | 79.20 (10) | O4i—Al—O4 | 80.02 (14) |
O4iii—V—O4iv | 77.02 (13) | | |
Symmetry codes: (i) x, −y+3/2, z; (ii) x, −y+1/2, z; (iii) −x+1, y−1/2, −z; (iv) −x+1, −y+1, −z; (v) −x+1, −y, −z; (vi) −x+1, y+1/2, −z+1; (vii) −x+1, −y+1, −z+1; (viii) x+1/2, y, −z+1/2. |
Experimental details
Crystal data |
Chemical formula | MoVAlO7 |
Mr | 285.86 |
Crystal system, space group | Orthorhombic, Pnma |
Temperature (K) | 293 |
a, b, c (Å) | 12.7360 (2), 5.3790 (4), 8.1660 (6) |
V (Å3) | 559.43 (6) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 4.04 |
Crystal size (mm) | 0.08 × 0.05 × 0.02 |
|
Data collection |
Diffractometer | Nonius KappaCCDr diffractometer |
Absorption correction | Multi-scan Blessing (1995) |
Tmin, Tmax | 0.842, 0.930 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3861, 1054, 878 |
Rint | 0.067 |
(sin θ/λ)max (Å−1) | 0.746 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.035, 0.083, 1.05 |
No. of reflections | 1054 |
No. of parameters | 56 |
Δρmax, Δρmin (e Å−3) | 1.16, −2.76 |
Selected geometric parameters (Å, º) topMo—O1 | 1.744 (3) | V—Vii | 2.9315 (6) |
Mo—O2 | 1.752 (3) | V—Alii | 3.0138 (15) |
Mo—O3 | 1.757 (3) | Al—O1iii | 1.843 (3) |
V—O5 | 1.586 (4) | Al—O3iv | 1.855 (3) |
V—O4 | 1.822 (2) | Al—O2 | 1.893 (3) |
V—O4i | 1.980 (2) | Al—O4 | 1.918 (2) |
| | | |
O1—Mo—O1v | 105.29 (19) | O1iii—Al—O1vii | 90.00 (18) |
O1—Mo—O2 | 109.67 (10) | O1iii—Al—O3iv | 91.27 (12) |
O1—Mo—O3 | 110.85 (10) | O1iii—Al—O2 | 90.18 (12) |
O2—Mo—O3 | 110.39 (16) | O3iv—Al—O2 | 177.96 (16) |
O5—V—O4 | 105.85 (11) | O1iii—Al—O4v | 94.98 (11) |
O4vi—V—O4 | 106.13 (14) | O1vii—Al—O4v | 174.91 (12) |
O5—V—O4i | 106.78 (13) | O3iv—Al—O4v | 89.70 (11) |
O5—V—O4ii | 106.78 (13) | O2—Al—O4v | 88.74 (12) |
O4—V—O4ii | 79.20 (10) | O1iii—Al—O4 | 174.90 (11) |
O4i—V—O4ii | 77.02 (13) | O4v—Al—O4 | 80.02 (14) |
Symmetry codes: (i) −x+1, y−1/2, −z; (ii) −x+1, −y+1, −z; (iii) −x+1, y+1/2, −z+1; (iv) x+1/2, y, −z+1/2; (v) x, −y+3/2, z; (vi) x, −y+1/2, z; (vii) −x+1, −y+1, −z+1. |
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A detailed study of the Mo1 + xV2 - xO8 and V2 - xMoxO5 phases of the MoO3–V2O5–V2O4 system has been undertaken in order to fix their homogeneity range domains, the existence of super- or modulated structures and also their magnetic and electric behaviours (Galy et al., 2001). For the former phase, synthesized at 903 K, the x limit values have been established: 0.12 < x < 0.18; in the meantime, magnetic properties have proved the presence of V4+ cations, leading to the formulation Mo6+1 + xV5+2–2xV4+xO8, this latter phase being a semiconductor (Ea = 0.22 eV). During the attempt to test the electrical response, a pellet was placed in an alumina crucible and heated up to 973 K; surprisingly, an extremely strong reaction occurred between the Mo1 + xV2 - xO8 pellet and the crucible. In the complex mixture obtained, one small crystal, nicely prismatic and with a green colour, was detected. This crystal was quite different from the crystals of the phases of our system. It was readily studied by X-ray single-crystal techniques in order to determine its structure and therefore its chemical composition (see details of the structure determination below).
The crystal structure shows three different types of coordination for the Mo, V and Al atoms. A perspective view oriented along [010] is shown in Fig. 1. The Mo atom is surrounded by four O atoms, making a regular MoO4 tetrahedron (see Table 1); the V atoms are inside an oxygenated VO5 square-pyramid, while the Al atom is at the center of a regular octahedron. The VO5 square pyramids share opposite basal edges, alternately pointing up and down, making an infinite string elongated along the helicoidal twofold axis parallel to [010]. These strings are surrounded by a kind of ring alternately built up of four MoO4 tetrahedra and four AlO6 octahedra through shared corners, ···Al–O2–Mo–O3–Al··· (Fig. 2). Along [010], the two other O atoms of the MoO4 tetrahedron (O1 repeated by the mirror plane perpendicular to y axis), connect two successive AlO6 octahedra that share edges with the VO5 square pyramids via O4 atoms. MoVAlO7 exhibits a three-dimensional network. We note the short V—O5 distance typical of the classical multiple bond between V5+ and oxygen in the apical position of the VO5 square pyramid, pulling V above the basal square plane of O atoms (Table 1). The unexpected composition of such a crystal drove us to confirm immediately by solid-state synthesis the formation of this phase (see Experimental). A green powder was obtained and all the reflections of the X-ray powder pattern were indexed with the single-crystal data. The measured density of MoVAlO7 is in good agreement with the calculated density. The MoVAlO7 formula was then definitively established. Following this work and knowing the compound formula a search was undertaken in the literature. A structure determination by X-ray powder diffraction of the same compound was published by Knorr et al. (1998), but the previous authors were unable to grow single crystals because the phase melts incongruently at 963 K. Comparison of both structural determinations shows a reasonable agreement of the general atomic architecture. The cell parameters are similar: a = 12.7312 (6), b = 5.3763 (3), c = 8.1644 (3) Å and V = 558.8 Å3 (Knorr et al., 1998), but, of course, the single-crystal study allows us to obtain very accurate data on bond lengths and angles. It is then readily seen that all metal–oxygen distances are in excellent agreement with the known distances in well established structures. Especially, the short V—O distance of 1.586 (4) Å compares well with the corresponding distance in V2O5, i.e. 1.577 (3) Å (Enjalbert & Galy, 1986); the V—O distance of 1.48 Å found by Knorr et al. (1998) is really too short. On this basis, calculation of bond valence sums according to Brown & Altermatt (1985) gives a good agreement for the oxidation states of Mo, V and Al. These calculations strengthen also the fact that Knorr et al. (1998) had underestimated the uncertainties of their measurements by some 4σ. In both MoO4 and AlO6 polyhedra, the rather regular O···O distances fluctuate between O3···O2 = 2.882 (3) Å when MoO4 connects the apices of two AlO6 octahedra to O4···O4i = 2.464 (3) Å for the edge shared between the VO5 square pyramid and AlO6. This last value is associated with the smallest bond angles O4—Al—O4i = 80.0° and O4—Viv—O4i = 77.0°, such angles being reasonably attributed to a strong repulsion between the V5+ and Al3+ cations. The same phenomenon appears also for the edge sharing VO5 square pyramids, the O4···O4iv distance diminishing to 2.425 (3) Å with O4—V—O4iv = 79.2°. The VO5 square pyramids are really extremely distorted; note that the O4···O4ii interatomic distance is 2.915 (3) Å, and that the V—O bonds towards the basal `square' plane are rather different with V—O4 = 1.822 (2) Å and V—O4iii = 1.980 (2) Å. Such distortions explain why some authors, substituting bigger cations like Fe3+ and Cr3+ for Al3+, have found a triclinic distortion of the network (Le Bail et al. 1995).