Replacing [VO(O i Pr)3] with [VO(O n Pr)3] in the same reaction that affords tetrameric complex 10 results in the formation of the hexameric complex 12. The same central (bent) V-O-Nb/Ta-O-Nb/Ta-O-V chain prevails, but with two additional V ions asymmetrically capping both sides of the Nb-Nb vector, linked by one µ3-O 2- ion and two µ-O 2-ions, respectively. The fully deprotonated TBC [8] ligand coordinates in the same way as in 10 and 11. The three O n Pr ligands are of two types, two are µ-bridging between neighbouring Nb-V-Nb ions, with the third terminally bonded to the same V ion. The Nb ions are six coordinate and in octahedral {NbO6} geometries. The V ions are of three types, two are four coordinate and in tetrahedral {VO4} geometries, one is five coordinate and in square pyramidal {VO5} geometry, while one is six coordinate and in an octahedral {VO4N2} geometry with its coordination sphere completed by two MeCN molecules. It is this metal ion that is V IV .