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

Abstract

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 4hydroxyphenyl substituted ferrocenyl-containing half unit Fc-C(=O)CH=C(4-C 6 H 4 OH)NH-CH 2 CH 2 NH 2 (Fc = ferrocenyl = (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )), metal(II) acetate and 5nitrosalicylaldehyde (for 2-4) or the organometallic salicylaldehyde [Cp*Ru(η 6 -2-OH-C 6 H 4 CHO)]PF 6 (for 5) (Cp* = η 5 -C 5 Me 5 ). 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 of 3 reveals that the four-coordinate copper atom adopts a square planar geometry with two nitrogen and two oxygen atoms as donors occupying cis positions. 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 chromophores 2-5 have been determined by harmonic light scattering measurements in N,Ndimethylformamide solutions at 1.91 μm incident wavelength, and rather high, non-resonant quadratic hyperpolarisability β values ranging from 140-280 x 10 -30 esu were determined.

Ferrocene functionalized enantiomerically pure Schiff bases and their Zn(ii) and Pd(ii) complexes: a spectroscopic, crystallographic, electrochemical and computational investigation

“…Similar behaviors have previously been observed for Zn(II) and Pd(II) complexes of N 2 O 2 tetradentate Schiff base ligands. 39,51,52 Crystal structural studies of the ferrocene-containing Schiff bases 3 and 4…”

“…Such a solvatochromism is also characteristic of push-pull complexes and could be related to potential NLO properties. 39,51,56 Electrochemical study…”

“…44,45 The electrochemical behavior of the two bimetallic derivatives 5 and 6 confirms a trend already observed. 39,51,52 That is a weak anodic shift in the case of Zn(II) and a large one in the case of Pd(II) complexes, whatever the substituent borne by the salicylidene ring. In the Zn(II) series, the same 70 mV anodic shift was found for both 5 substituted by the methoxy donor group and its previously reported relative bearing the electron withdrawing nitro group.…”

Synthesis, Characterization, and In Vitro Cytotoxicity of Unsymmetrical Tetradentate Schiff Base Cu(II) and Fe(III) Complexes

“…In UV-Vis spectra of unsymmetrical tetradentate Schiff base Cu(II) complexes, besides the main absorption bands of interligand charge transfer transitions with λ abs at about 245-250 nm and 300-360 nm (n ⟶ π * ), a new broad lowenergy absorption band with λ abs is observed at 380-500 nm which can be assigned to ligand-to-metal charge transfer (LMCT) and metal-to-ligand (MLCT) transitions [29,30]. Magnetic measurements and electronic spectra were conducted in order to obtain information about geometry of the complexes.…”

Nickel(II)-Based Building Blocks with Schiff Base Derivatives: Experimental Insights and DFT Calculations

“…The solid-state FT-IR spectra exhibited the characteristic strong intensity bands in the ranges 1610–1550 cm −1 , due to the ν (C ··· C), ν (C ··· N), ν (C ··· O) stretching vibrations of the Schiff base ligand, suggesting its ONO- tridentate coordination mode to the Ni(II) metal ion [ 49 , 50 , 51 ]. More specifically, the symmetrical N-O stretching mode of the nitro group was observed at 1300 and 1310 cm −1 for 4 and 5 , respectively [ 53 ]. Moreover, the vibration attributed to ν (C≡C) is seen at 2227 cm −1 in the spectrum of 5 and at 2111 cm −1 in that of 8 ( Figure S1 , Supplementary Materials ).…”