Experimental and Theoretical Evaluation of Four NLO-Active Divalent Transition-Metal Complexes Supported by an Enantiomerically Pure Tetradentate Schiff Base Ligand

Abstract

Abstract This paper reports on a series of five chiral Schiff base push‐pull compounds derived from enantiomerically pure (1 R ,2 R )‐(−)‐1,2‐diaminocyclohexane. The Ni II , Cu II , Zn II and Pd II complexes supported by a ferrocene‐containing unsymmetrically‐substituted N 2 O 2 quadridentate Schiff base ligand were prepared via template reactions and isolated in 74–87 % yields. A combination of EA, IR, UV/vis and 1 H/ 13 C{ 1 H} NMR spectroscopy, HRMS spectrometry, cyclic voltammetry and single‐crystal X‐ray analysis (for the proligand 2 and its Ni II derivative 3 ), together with computational methods (DFT and TD‐DFT) was used to fully characterize and study the properties of all products. Both 2 and 3 crystallize in the orthorhombic non‐centrosymmetric space group P 2 1 2 1 2 1 , with two ( R , R )‐(−)‐chiral carbon atoms in their structure. Second‐order nonlinear polarizabilities β have been measured by using Harmonic Light Scattering at 1.91 μm, with the Pd(II) species showing the higher NLO response of 460×10 −30 esu.