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 Ni II 3,5-di( tert -butyl)-2-oxyazobenzene complexes, gas-phase quantum chemical calculations were performed for related model Cu II , Co II , Fe II , Mn II , Cr II , and Zn II 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 Fe II , Cr II , Zn II and doublet and quartet for Cu II , Mn II , Co II . 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 Cu II -, Co II -, and Fe II -based complexes have an unusual dome-shaped structure.