Electronic Structure of the Highly Reduced Polyoxoanion [PMo12O40(VO)2]: A DFT Study

The chemistry of polyoxoanions has been studied extensively.1-12 A large body of experimental knowledge has been accumulated on these oxide clusters, which can in many instances be reduced, maintaining their integrity with only subtle changes in their structure.7a,12 Trends in the obtention of blue reduced species have been empirically established over time, and the nature of electronic delocalization within the cluster has been discussed. Both hopping and ground-state delocalization mechanisms have been proposed to explain their electronic structure.1 However, there is still a need for a systematic analysis of the effects of reduction on the molecular and electronic structure, stability, and reactivity of these clusters. Ab initio theoretical studies in this field are still scarce and are restricted to some fully oxidized polyanions.13-15 The aim of this note is to present the first theoretical calculations of this type on the redox properties of a Keggin anion. For that, a bicapped, highly reduced Keggin complex [PMo12O40(VO)2], 1, whose synthesis and characterization have been reported recently by Hill et al.,16 was chosen. In contrast with the isostructural [V15O42] cluster,17 in which all of the vanadium atoms are formally d0 metals, in anion 1 the metal centers contain eight electrons (see Figure 1 for a 3D representation of the anion). In their study Hill suggests, on the basis of valence bond calculations, that two of the electrons are in vanadium centers while the other six electrons are on molybdenum. The results of our density functional calculations (DFT) on the bicapped cluster [PMo12O40(VO)2] agree with this.