Abstract
The synthesis of a niobium-(V) substituted polyoxovanadate-alkoxide (NbPOV-alkoxide; [NbV(5)O(7)(OCH(3))(12)]) is reported. Addition of 5,10-dihydrophenazine to [NbV(5)O(7)(OCH(3))(12)] results in formation of the 2 H(+)/e(-) reduced assembly, [NbV(5)O(6)(OH(2))-(OCH(3))(12)], via proton-coupled electron transfer. [NbV(5)O(6)(OH(2))-(OCH(3))(12)] has a bond dissociation free energy (BDFE-(O-H)(avg)) of 62.3 kcal mol(-1), resembling that of its homometallic congener, [V(6)O(6)(OH(2))-(OCH(3))(12)] (BDFE-(O-H)(avg) = 62.3 kcal mol(-1)). Single-crystal X-ray diffraction reveals that [NbV(5)O(6)(OH(2))-(OCH(3))(12)] exists as a mixture of two structural isomers, with the vanadium-aquo moiety formed in either the trans- or cis- positions relative to the Nb-(V) dopant. The formation of two regioisomers is a departure from prior observations of H-atom uptake at the surface of heterometal-doped polyoxovanadate-alkoxides, and is credited to distortions in intercluster metal oxygen bond lengths. Improved selectivity for the trans- isomer is achieved by decreasing the dielectric constant of the reaction solvent. Computational analysis predicts the preferential formation of trans-[NbV(5)O(6)(OH(2))-(OCH(3))(12)] in solvents with low dielectric constants as a result of changes to the dispersed charge across the assembly.