Consequences of ligand derivatization on the electronic properties of polyoxovanadate-alkoxide clusters

Abstract

Polyoxovanadate-alkoxide (POV-alkoxide) clusters are promising charge-carrier candidates for non-aqueous redox flow batteries (NRFBs), due in part to their easily-modified bridging alkoxide ligands. Herein, we report a series of new POV-alkoxide clusters featuring polar functional groups bound to the tertiary carbon of a tripodal, tris(hydroxymethyl)methane ligand (TRISR; R = C2H5, NO2, NMe3+, NC5H4 (Py), PyMe+). These clusters were synthesized to better understand the role that peripheral ligands with varying electronic properties play in tuning the electrochemical profile of the hexavanadate core. The results herein demonstrate that functional groups removed from the cluster core do not disrupt the characteristic electrochemical behavior of the mixed-valent POV-alkoxides, establishing the synthetic modularity of this structural platform. However, in contrast to molecular species previously reported, these polar and charged functional groups do not improve solubility or stability of the charge carriers in acetonitrile. This work furthers our knowledge of coordination chemistry of POV-ethoxide clusters, presenting design criteria critical for accessing polynuclear entities ideal for NRFB charge carriers.