Spectroscopic and DFT studies of zinc(II) complexes of diamines and thiocyanate; crystal structure of (cis-1,2-diaminocyclohexane)bis(thiocyanato-κN)zinc(II)

Zinc(II) complexes of diamines, cis-1,2-diaminocyclohexane (Dach) and N,N,N,N-tetramethylethylenediamine (Tmen), [Zn(Dach)(NCS)₂] (1) and [Zn(Tmen)(NCS)₂] (2) have been prepared and characterized by elemental analysis, IR, ¹H & ¹³C NMR spectroscopy. The crystal structure of [Zn(Dach)(NCS)₂] (1) was determined by X-ray crystallography. In 1, the Zn(II) atom is bound to one 1,2-diaminocyclohexane molecule and to two terminal thiocyanate ions via the nitrogen atoms adopting a slightly distorted tetrahedral geometry. In the crystal structure, molecules are linked through intermolecular N[sbnd]H⋯S hydrogen bonds, forming chains running along the a axis. The structures of 1 and 2 as well as of [Zn(En)(NCS)₂] (3) (En = 1,2-diaminoethane) were predicted using theoretical (DFT) method. The interaction energies (ΔE) for NCS anions obtained by B3LYP-D3 method are about −140 kcal mol⁻¹, while the calculated ΔE values for neutral organic ligands are about twice smaller. The atomic charges and second-order interaction energies between orbitals were calculated with natural bond orbital (NBO) analysis.