Side‐Chain Metallopolymers Containing Second‐Order NLO‐Active Bimetallic NiII and PdII 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 N 2 O 2 ‐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 °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 200 × 10 –30 and 970 × 10 –30 esu, with the hyperpolarizability β 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.