Molecular structure of nickel(II) and copper(II) N,N′-ethylene-bis(acetylacetoneiminates) MO2N2C12H18 according to gas-phase electron diffraction data and quantum-chemical calculations

Abstract

The molecular structure of nickel(II) and copper(II) N,N′-ethylene-bis(acetylacetoneiminates), NiO2N2C12H18 and CuO2N2C12H18, at 442(5) K and 425(5)K, respectively. Both molecules have C2 symmetry with a nearly planar MN2O2 coordination site and internuclear distances rh1(M-O) = 1.862(10)/1.923(17) A and rh1(M-N) = 1.879(10)/1.947(18) A for Ni(acacen) and Cu(acacen), respectively. The structure of free molecules is close to the structure of molecules in crystal. The DFT/3LYP quantum-chemical calculations (CEP-31G and 6-31G* basis sets) gave a molecular structure that agreed satisfactorily with the one found in experiment. The low-spin 1A and high-spin 3A states of the Ni(acacen) molecule were considered. It was found that a change in multiplicity caused significant changes in the geometrical and electronic structure of the MN2O2 coordination site. As shown by experiment and calculations for the NiO2N2C12H18 molecule, the low-spin 1A state is the ground state. The internal rotation of CH3(CN) and CH3(CO) methyl groups was studied by the 3LYP/CEP-31G method. It was shown that steric hindrances led to a high rotation barrier of the CH3(CN) group.