Exploration of CH⋯π interactions involving the π-system of pseudohalide coligands in metal complexes of a Schiff-base ligand

Abstract

A series of four mononuclear Schiff-base complexes, namely, [Zn(L)(NCS)₂] (1), [Zn(L)(N₃)₂] (2), [Cu(L)(NCS)₂] (3) and [Ni (L)(2bpy)(NCS)](ClO₄) (4), [where L = N,N-dimethyl-N′-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine and 2bpy = 2-benzoylpyridine] were synthesized with the aim of investigating the role of different non-covalent weak interactions responsible for the crystal packing of the complexes. All of them were structurally characterised by X-ray diffraction analysis. In addition to conventional CH₃⋯π and π⋯π interactions, the importance of unconventional C–H⋯π interactions in the crystal packing of compounds 1–4 was investigated by means of Hirshfeld surface analysis and DFT calculations. In these unconventional C–H⋯π interactions, the π-system (electron donor) is provided by the pseudohalide coligands. The interactions formed by the π-system depend on the nature of the pseudohalide (N₃, NCO, NCS or NCSe) as demonstrated by molecular electrostatic potential calculations. Additionally, we have explored the photophysical properties of these complexes. Finally, we have combined a search in the Cambridge Structural Database and DFT energy calculations to analyse the rare ambidentate behaviour of SCN within the same complex.