Main‐Chain Oligomers from Ni^II‐ and Cu^II‐Centered Unsymmetrical N₂O₂ Schiff‐Base Complexes: Synthesis and Spectral, Structural, and Second‐Order Nonlinear Optical Properties

Abstract

Abstract Oligomeric main‐chain Schiff‐base compounds 4 and 5 have been synthesized by the trans‐esterification of their respective doubly functionalized monomeric precursors [M{(η 5 ‐C 5 H 5 )Fe(η 5 ‐C 5 H 4 )C(=O)CH=C(4‐C 6 H 4 OH)NCH 2 CH 2 N=CH‐(2‐O,4‐CO 2 H–C 6 H 3 )}] [M = Ni ( 2 ), Cu ( 3 )] in dmf. The new compounds were characterized by elemental analysis, FTIR and multidimensional NMR spectroscopy, mass spectrometry, and cyclic voltammetry. Compounds 2 , 3 , and 6 , the corresponding amide of 2 , were characterized by X‐ray structural investigation. Gel permeation chromatography established that oligomers 4 and 5 are formed of approximately six monomeric units, and differential scanning calorimetry and thermal gravimetric analysis indicated that they are thermally stable with decomposition temperatures exceeding 230 °C. Harmonic light scattering measurements showed that compounds 2 – 5 exhibit rather high second‐order nonlinear responses, between 224 × 10 –30 and 399 × 10 –30 esu, with hyperpolarizability β 1.91 values that increase significantly on passing from the monomeric to the oligomeric species.