Transition metal(II) complexes featuring push-pull dianionic Schiff base ligands: synthesis, crystal structure, electrochemical, and NLO studies

摘要

The present study reports the synthesis and characterization of a family of three new neutral Zn(II), Cu(II), Co(II) bimetallic (2-4), and one ionic Co(II) trimetallic (5) complexes of ferrocene-containing unsymmetrically-substituted N(2)O(2)tetradentate Schiff base ligands. They were all prepared via a three-component one-pot template reaction involving the 4-hydroxyphenyl substituted ferrocenyl-containing half unit Fc-C(=O)CH = C(4-C6H4OH)NH-CH2CH2NH2(Fc = ferrocenyl = (eta(5)-C5H5)Fe(eta(5)-C5H4)), metal(II) acetate, and 5-nitrosalicylaldehyde (for2-4) or the organometallic salicylaldehyde [Cp*Ru(eta(6)-2-OH-C6H4CHO)]PF6(for5) (Cp* = eta(5)-C5Me5). The four complexes were isolated as air and moisture insensitive solids in yields > 80%. They were characterized using several analytical techniques such as CHN analyses, ESI mass, FT-IR, UV-vis, and NMR spectroscopy, including single crystal X-ray diffraction analysis. The crystal structure of3reveals that the four-coordinate copper ion adopts a square planar geometry with two nitrogen and two oxygen atoms as donors occupyingcispositions. An electrochemical study utilizing cyclic voltammetry showed for each compound a reversible redox process ascribed to the Fe(II)/Fe(III) couple of the appended donor ferrocene. The largest anodic potentials were measured for the two Co(II) species. The second-order NLO responses of the push-pull chromophores2-5have been determined by harmonic light scattering measurements in N,N-dimethylformamide solutions at 1.91 mu m incident wavelength, and rather high, non-resonant quadratic hyperpolarizability beta values ranging from 140 to 280 x 10(-30 )esu were determined.