Electronic structure of substituted catecholate complexes of hexacoordinated silicon: a quantum chemical study

Anionic complexes LSi(Cat R ) 2 (L is a chelate N -methyl- N -(acetamido)methyl-C,O group or (2-oxo-1-hexahydroazepinyl)methyl-C,O group; Cat R is a substituted catecholate ligand) were studied by quantum chemistry at the PBE0/6-311G(d,p) and RI-MP2/def2-TZVPP levels with inclusion of nonspecific solvation using the PCM model. It was shown that the nature of substituents in the catecholate phenyl ring and the L group weakly influences the geometry of the coordination environment of the silicon atom. The higher the electron-withdrawing effect and the number of substituents in the catecholate ligands, the higher the vertical or adiabatic ionization potentials. It was established that the formation of oxidized forms of the complexes LSi(Cat R ) 2 is characterized by weakening of the Si-O bonds between the silicon atom and the Cat R (Cat R -2) ligand opposite to the Si-O bond with the group L and by shortening of the Si-O bonds between the silicon atom and the other catecholate ligand (Cat R -1). An analysis of the average local ionization energies and a topological analysis of the electron localization function showed the Cat R -2 ligand is less sensitive to the interaction with free radicals than Cat R -1 due to redistribution of electron density from the region of its oxygen atoms and phenyl ring.