Varying coordination modes of amide ligand in group 12 Hg(ii) and Cd(ii) complexes: synthesis, crystal structure and nonlinear optical properties

Abstract

Reactions of the amide ligand, H₂L (H₂L = N,N′-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide) with CdCl₂ and Hg(CH₃COO)₂, in 1 : 1 ratio, at 298 K yield dimeric [Hg(L)]₂ (1) and trimeric [Cd₃(H₂L)₄Cl₆] (2), respectively. In 1, the H₂L is coordinated to Hg(II) via six N-atoms of central and terminal pyridines as well as of deprotonated amido groups, whereas the carbonyl groups remain free. However, in 2, the H₂L is coordinated to Cd(II) through terminal pyridine N atoms and O atoms from carbonyl groups, whereas the nitrogen atoms of the central pyridine, two terminal pyridine and of all amido groups remain free. Molecular structures of 1 and 2 are confirmed by single crystal X-ray studies. The varying coordination modes of H₂L give rise to different electrochemical behavior of 1 and 2, which has also been rationalized by theoretical calculations. Moreover, nonlinear optical (NLO) behavior of both complexes has been investigated using ultra-short femtosecond laser pulses, which ensures that the NLO response is exclusively from their electronic component.