Molecular structure and linkage isomerization in copper(II) complexes containing N,N-dialkyl-N′-benzylethylenediamine and thiocyanate ligands: a combined crystallographic, spectroscopic and DFT study

A combined experimental and computational study of three thiocyanate-Cu(II) complexes with general formula [Cu(Ln)2(NCS)]ClO4, (L1 = N,N-dimethyl,N′-benzyl-ethylenediamine, L2 = N,N-diethylyl,N′-benzyl-ethylenediamine, L3 = N,N-diisopropylyl,N′-benzyl-ethylenediamine) was carried out. The compounds were synthesized and structurally characterized by physico-chemical and spectroscopic methods. X-ray crystallography of [Cu(L1)2(NCS)]ClO4 showed that the copper atom achieves a distorted square pyramidal environment through coordination of four amine N atoms and a N atom of the terminal SCN− ion. To investigate the effect of steric crowding on the coordination mode of thiocyanate at the copper(II) center, DFT calculations are carried out on the complexes. Two different cases were considered, namely when nitrogen is the donor atom and when sulfur is the donor atom. In all cases, the N-coordinated isomers were always more stable than the S-coordinated ones. The electronic spectra of the complexes were analyzed and assigned by means of DFT/TD-DFT, together with molecular orbital analysis.