Electronic Consequences of Ligand Substitution at Heterometal Centers in Polyoxovanadium Clusters: Controlling the Redox Properties via Heterometal Coordination Number.

The rational control of the electrochemical properties of polyoxovandate-alkoxide clusters is dependent on understanding the influence of various synthetic modifications on the overall redox processes of these systems. In this work, we examine the electronic consequences of ligand substitution at the heteroion in a heterometal-functionalized cluster. The redox properties of [V 5 O 6 (OCH 3 ) 12 FeCl] ( 1-[V 5 FeCl] ) and [V 5 O 6 (OCH 3 ) 12 Fe]X ( 2-[V 5 Fe]X ; X = ClO 4 , OTf), were compared in order to assess the effects of changing the coordination environment around the iron center on the electrochemical properties of the cluster. Coordination of a chloride anion to iron leads to an anodic shift in redox events. Theoretical modelling of the electronic structure of these heterometal-functionalized clusters reveals, that differences in the redox profiles of 1-[V 5 FeCl] and 2-[V 5 Fe]X arise from changes in the number of ligands surrounding the iron center (e.g. 6-coordinate vs . 5-coordinate). Binding of the chloride to the sixth coordination site changes the orbital interaction between the iron and the delocalized electronic structure of the mixed-valent polyoxovanadate core. Tuning of the heterometal coordination environment can therefore be used to modulate the redox properties of the whole cluster.