Copper(II) and Zinc(II) Complexes with a Photoactive Bridging Ligand Based on Carbazole: Synthesis, Structures, Electronic and Magnetic Properties

Abstract

AbstractThe synthesis of the new Schiff base ligand N‐(4‐methoxyphenyl)‐3,4‐bis(salicylidenimino)carbazole (H2SalCarbOMe) is described. It readily reacts with copper(II) andzinc(II) ions to form metallacycles of the general formula [M2(SalCarbOMe)2] (M = Cu, Zn). Their structures are determined by X‐ray crystallography and show significant differences for the coordination at the metal ion with a nearly tetrahedral arrangement for ZnII, but a considerable distortion towards square‐planar geometry for CuII. This in turn leads to substantial differences for the dihedral angles observed between the salicylidene and carbazole moieties. As a consequence different arrangements in the unit cell are observed, which becomes particularly obvious when the additional solvent molecules of crystallization are considered. For the ZnII compound this leads to the incorporation of a chloroform and a methanol molecule in fixed positions, whereas in the structure of the CuII compound a higher number of solvent molecules (chloroform, methanol, and water) in highly disordered crystallographic positions is observed. The optical and magnetic properties have been characterized for both complexes. They both show two band fluorescence in the visible region with emission maxima at 531 and 586 nm for the ZnII compound and 488 and 580 nm in the CuII complex. The electronic properties have been further elucidated by quantum chemical calculations. For the two copper(II) ions an antiferromagnetic interaction through the carbazole bridging ligand with an exchange coupling constant of J = –3.1 cm–1 is observed. ESR spectroscopy reveals a rhombic signal with g values [gx, gy, gz] = [2.057, 2.125, 2.200] consistent with the distorted coordination geometry around the copper(II) ions.