Quantum chemical study of the unusual structure of 3d metal complexes in the gas phase

Based on the previous experimental and theoretical studies of the unusual dome-shaped structures of Pd II and NiII 3,5-di(tert-butyl)-2-oxyazobenzene complexes, gas-phase quantum chemical calculations were performed for related model CuII, CoII, FeII, MnII, CrII, and ZnII complexes. The calculations were carried out with full geometry optimization at the TPSSh/def2tzvp(Cu,Co,Fe,Mn,Cr,Zn)/6-311G*(C,N,O,H) level of theory. All compounds were calculated in the low-spin and high-spin states — singlet and triplet for FeII, CrII, ZnII and doublet and quartet for CuII, MnII, CoII. Metal complexes with a closed shell (Zn), a half-filled shell (Cr), and a half-filled d-subshell (Mn) have a tetrahedral structure in the gas-phase ground energy state, whereas CuII-, CoII-, and FeII-based complexes have an unusual dome-shaped structure. © 2021, Springer Science+Business Media LLC.