Structural and Electronic Properties of Aqueous Transition−Metal−Substituted Polyoxotungstates

Polyoxometalates (POMs) are a discrete class of polyanionic metal−oxo aggregates with a large diversity of topologies, structural flexibility, and functionality at the nanoscale. Controlled base treatment of these compounds produces monolacunary polyanions that behave as multi−dentate ligands, generating a class of compounds known as transition metal substituted POMs. These compounds demonstrate excellent redox stability, making them are integral precursors for electrochemical processes. In this work, Density Functional Theory (DFT) calculations have been employed to systematically studied the accuracy of various exchange−correlation functions in describing the properties of transition−metal−substituted polyoxotungstates which are integral precursors for electrochemical processes. Molecular geometries were optimized using several generalized gradient approximations (GGA), hybrid, and long−range−corrected GGA (LC−GGA) with whom all agreed well with experimental crystallographic results. We report the standard reduction potentials, U0red vs NHE, for the pH−independent redox processes present in Keggin [M(H2O)PW11O39]5−; M = Mn(III/II), Fe(III/II), Co(III/II), and Ru(III/II)) anions calculated as a function of Hartree−Fock (HF) exchange and provide insight into the electronic properties controlling it.