Side-Chain Metallopolymers Containing Second-Order NLO-Active Bimetallic NiII and PdII Schiff-Base Complexes: Syntheses, Structures, Electrochemical and Computational Studies

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^IIand Pd^IImetal 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^–30and 970 × 10^–30esu, with the hyperpolarizability β_1.91value increasing significantly on passing from Ni^IIcomplex 3 to its respective metallopolymer 5. The structural and electronic properties of 2–4 are analyzed by DFT and TD-DFT calculations.