Coordinating and non-coordinating anion controlled synthesis of different nuclearity cadmium(II) complexes of 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol: Crystal structure and photophysical study

The tridentate Schiff base ligand 2-((E)-((pyridin-2-yl)methylimino)methyl)phenol (HL) was used to synthesize four new cadmium(II) complexes, namely [Cd4L6](ClO4)2 (1), [CdL(SCN)]n (2), [CdL(dca)]n (3) and [CdL(N3)]n (4), with the aim of exploring the role of the coordinating and non-coordinating anion in governing the architecture as well as the photophysical behavior of the complexes. In addition to common physicochemical techniques, complexes 1 and 2 have further been characterized by X-ray single crystal structural analysis. Complex 1 is a tetranuclear cationic Cd(II) species where each metal ion has a distorted octahedral geometry. Three Cd atoms have the N4O2 chromophoric environment, whereas the fourth and central Cd has an O6 chromophore. Complex 2 is a polynuclear species having a 2D network of (4,4) topology where dinuclear [Cd2L3] metal entities located at the nodes are bridged by SCN anions. The ligand and all four complexes are highly fluorescent. Quantum yield calculations reveal that the fluorescence efficiency of the complexes is higher than that of the ligand and the efficiency is largely influenced by the nature of the co-ligand.