A computational investigation into the redox chemistry of Mo- and W-tris(diselenolene) complexes

Since the 1960s, dithiolene complexes have been intensely studied; however, the same cannot be said about diselenolene complexes. Thus, the chemistry associated with the reduction of several Mo- and W-tris(diselenolene) complexes was investigated. In particular, relative reduction potentials, changes in key geometrical properties, the contribution of the metal center to the redox active MO, and HOMO–LUMO energy gaps are investigated. It is noted that the results obtained for the tris(diselenolene) complexes are compared to analogous Mo- and W-tris(dithiolene) complexes to understand the effect of substituting the sulfur atoms with selenium atoms. The reduction potentials of the complexes are more dependent upon the choice of the ligand than the metal. Overall, it is found that the substitution of chalcogen atom for the tris complexes investigated herein has only a subtle effect on the calculated reduction potentials between analogous redox couples. Upon reduction of the neutral and mono-anionic complexes, it is found that changes in key bond lengths, fold angles (θ), and trigonal twist angles (ΦAvg) are very similar for the tris(diselenolene) complexes investigated. Such changes have been previously observed for several Mo- and W-tris(dithiolene) complexes. Comparing the HOMO–LUMO energy gaps of the tris(diselenolene) complexes to the tris(dithiolene) complexes, the former complexes have on average a 0.07-eV smaller energy gap and are thus expected to be slightly more reactive to reduction. Lastly, in the neutral complexes, the Mo and W atoms contribute at most 26% to the redox active MO; thus, in the case of the tris(diselenolene) complexes, it can be concluded that the redox active MO is predominantly ligand based. The contribution of the metal-based AO becomes less as the complexes are reduced. In summary, given the high interest of dithiolene complexes in the areas of alternative energy and material science, the results presented herein provide motivation to further investigate the chemistry of diselenolene complexes.