Synthesis, structures and stability of three V-substituted polyoxoniobate clusters based on [TeNb9O33]17− units

Abstract

Three structurally intriguing polyoxoniobates (PONbs) based on the trivacant B-type α-Keggin ion {TeNb₉O₃₃}, H₄K(CN₃H₆)₂{[Cu₄(2,2′-bipy)₄(H₂O)₂][TeNb₉V₂O₃₇]}·29H₂O (1, 2,2′-bipy = 2,2′-bipyridine), H_0.5K₅Na_2.5{[Cu(en)H₂O]₃[TeNb₉V₃O₃₉]}·10H₂O (2, en = ethylenediamine), and K₃Na₅{[Cu(1,3-dap)H₂O]₃[TeNb₉V₃O₃₉]}·11H₂O (3, 1,3-dap = 1,3-diaminopropane), are assembled by the conventional aqueous solution methods using a series of N-containing organic ligands. In 1, each of the two {VO₄} units is attached to two coplanar NbO₆ octahedra on the {Nb₃O₁₃} cluster of the {TeNb₉O₃₃} unit. Differently, three {VO₄} units in 2 and 3 are linked to two edge-sharing NbO₆ octahedra, respectively. Compounds 1–3 represent the first oxo NbTeV clusters and also the first vanadoniobates based on the trivacant Keggin PONb units. All three compounds were characterised by single-crystal X-ray structural analysis, TGA and IR, ESI-MS and ⁵¹V NMR spectroscopy. Furthermore, the magnetic properties of compounds 1 and 2 were also studied.