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 N₂O₂ 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 = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)), metal(II) acetate, and 5-nitrosalicylaldehyde (for 2–4) or the organometallic salicylaldehyde [Cp*Ru(η⁶-2-OH-C₆H₄CHO)]PF₆ (for 5) (Cp* = η⁵-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 of 3 reveals that the four-coordinate copper ion 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,N-dimethylformamide solutions at 1.91 μm incident wavelength, and rather high, non-resonant quadratic hyperpolarizability β values ranging from 140 to 280 × 10⁻³⁰esu were determined.

Graphical Abstract

Keywords:

• Transition metals
• Schiff bases
• donor-acceptor systems
• X-ray diffraction
• nonlinear optics

Acknowledgments

The authors thank S. Sinbandhit (and P. Jehan CRMPO, Rennes) for helpful assistance with NMR and HRMS measurements, respectively. S.C. thanks VRIEA-PUCV and FONDECYT for the postdoctoral financing.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Additional information

Funding

This work was supported by the [Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT), Chile] under grant [1090310]; and [Fondo de Equipamiento Científico y Tecnológico (FONDEQUIP), Chile] under grants [EQM130154 and EQM120095]. Financial support from the Vicerrectoría de Investigación y Estudios Avanzados, Pontificia Universidad Católica de Valparaíso, Chile (VRIEA-PUCV), the Centre National de la Recherche Scientifique (CNRS), and the Université de Rennes 1 is also acknowledged. This research was performed as part of the Chilean-French International Research program “Multifunctional Molecules and Materials” (IRP M3-CNRS No. 1207).