Exploration of unconventional π–hole and C–H⋯H–C types of supramolecular interactions in a trinuclear Cd(ii) and a heteronuclear Cd(ii)–Ni(ii) complex and experimental evidence for preferential site selection of the ligand by 3d and 4d metal ions

Abstract

In this present work we report the synthesis and structural characterisation of a trinuclear cadmium(II) (1) and a di(phenoxido)-bridged dinuclear cadmium(II)–nickel(II) (2) complex derived from a bicompartmental (N₂O₄) Schiff base ligand, H₂L. It has been observed that, in bicompartmental ligands the relatively small inner core is suitable for 3d metal ions and outer core can be occupied by different metal centers like 3d, 1s, 2s, 4d and 4f. We have experimentally established the above fact. In homotrinuclear complex 1 both inner (N₂O₂) and outer (O₄) core has been occupied by cadmium(II) ions. Complex 1 upon reaction with NiCl₂·6H₂O produces heterodinuclear complex 2. Structural studies reveal that, in complex 1 terminal Cd units acquire trigonal prismatic geometry whereas the central Cd unit is eight coordinated. In case of complex 2 both nickel(II) and cadmium(II) ions are hexa-coordinated in a distorted octahedral environment. Both the complexes are studied using different spectroscopic techniques. Complexes 1 and 2 exhibit important and relatively unexplored group of supramolecular interactions like π–hole, C–H⋯π and C–H⋯H–C along with other hydrogen bonding interactions. Theoretical DFT calculations are devoted to analyze these non covalent interactions. Several computational tools like MEP surface analysis and NCI analysis are utilized to explain and illustrate such interactions.