Multi-reference calculations were performed in conjunction with large basis sets to investigate the electronic structure of the ground and low lying electronic excited states of MO2+ species, where M= Ti-Cu. Transition metal dicationic systems have been shown to be highly efficient in the activation of C-H bonds in saturated hydrocarbons. In addition, in biological systems, transition metal dications such as the FeO2+ oxo unit is widely studied due to its presence in intermediate forms of enzymes. This is the first systematic investigation on these systems and provides deep insight into the reactivity and stability of the MO2+ units. The first-row transition metal dications can be grouped into three groups: early, middle, and late transition metals. Early transition metals (Ti, V, Cr) are characterized by having stable and well separated oxo ground states, middle transition metals (Mn, Fe) have oxyl ground states with the presence of low-lying oxo excited states, and late transition metals (Co, Ni, Cu) with well separated oxyl states, lacking the presence of oxo states. By using multireference configuration interaction (MRCI) and the Davidson correction, along with coupled-cluster singles, doubles, and perturbative triple excitations (CCSD(T)), for single reference systems, periodic trends for bond lengths are reported, along with energetics, and wavefunction composition for these species, as well as accurate spectroscopic constants. The periodic trends found from the initial, middle, and late transition metals are of paramount importance in catalysis, i.e, new insight into dissociation channels and identification of different stable minima in the potential energy surface, which is crucial for experimentalists in future catalysis investigations.

Electronic structure of the dicationic first-row transition metal oxides

ACS Spring 2022

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