Side-Chain Metallopolymers Containing Second-Order NLO-Active Bimetallic Ni-II and Pd-II Schiff-Base Complexes: Syntheses, Structures, Electrochemical and Computational Studies
Abstract
Unsymmetric Schiff-base metalloligand precursor 2 is synthesized by condensation of phenol-functionalized ferrocenylenaminone 1 with 2-hydroxy-5-nitrobenzaldehyde. Heterobimetallic complexes 3 and 4 result from the N2O2-tetradentate coordination of Ni-II and Pd-II metal ions with the doubly deprotonated form of 2, respectively. Linking 3 and 4 to polyacrylic acid through an esterification reaction leads to the formation of the corresponding side-chain metallopolymers 5 and 6. The new compounds were fully characterized (IR, UV/Vis, NMR, MS, CV, SEC) and structures of 2-4 unequivocally determined by single-crystal X-ray diffraction techniques. Decomposition temperatures higher than 250 degrees C were found by DSC and TGA techniques for 3-6. Harmonic light scattering measurements showed that compounds 2-5 exhibit rather high second-order nonlinear responses, between 200x10(-30) and 970x10(-30) esu, with the hyperpolarizability (1.91) value increasing significantly on passing from Ni-II complex 3 to its respective metallopolymer 5. The structural and electronic properties of 2-4 are analyzed by DFT and TD-DFT calculations.