Synthesis and single crystal structures of V(OH)ndc·H2O, V(OH)ndc, and VOndc

Abstract

The vanadium analog of MIL-69, V(OH)ndc·H2O (ndc = 2,6-naphthalenedicarboxylate) was prepared solvothermally and the structure determined by single crystal X-ray diffraction (Space Group P21/c (#14), a = 6.7936(2) Å, b = 14.6816(4) Å, c = 23.9156(6) Å, β = 91.734(2)°, V = 2394.3(1) Å3). Anhydrous V(OH)ndc was obtained from V(OH)ndc·H2O by heating under nitrogen flow at 378 K in situ the crystal used to determine the structure of the as synthesized hydrated compound. The water molecules are removed on heating in a crystal to crystal transformation. Minor changes in the structure occur with no change in the V3+ oxidation state though the space group symmetry changes from P21/c to C2/c. (Space Group C2/c (#15), a = 24.684(4) Å, b = 7.079(2) Å, c = 6.853(1) Å, β = 104.35(1)°, V = 1160.2(4) Å3). The structure of VOndc (Space Group C2/c (#15), a = 24.628 (2) Å, b = 7.1434(5)Å, c = 6.7428(4) Å, β = 104.637(3)°, V = 1147.8 Å3) obtained by heating V(OH)ndc·H2O in air at 573 K, in contrast shows a change in oxidation state from V3+ to V4+ evidenced by bond valence sum calculations and by the appearance of a characteristic distorted VO6 octahedron and an O⋯V(IV) = O chain.