Density functional theory study on the structure of bis(1,1-diethyl-3-benzoyl-thioureato) copper(II). Planar or distorted tetrahedral CuS2O2 conformation?

Density functional theory calculations at the B3LYP level of theory combined with several basis sets were carried out on the structure of bis(1,1-diethyl-3-benzoyl-thioureato) copper(II). The results obtained clearly show two minima with local cis-CuS2O2 geometry, one resembling the X-ray experimental structure, in which the coordination polyhedron is a distorted tetrahedron, and the other with the CuS2O2 moiety nearly planar, resembling the corresponding ureato and a similar mercapto-β-diketone. A third minimum was found for a trans-CuS2O2 conformation. The calculated energy gap between the three structures is lower than 5 kJ/mol.