title: Structural, spectral, electric-field-induced second harmonic, and theoretical study of Ni(II), Cu(II), Zn(II), and VO(II) complexes with [N2O2] unsymmetrical schiff bases of S-methylisothiosemicarbazide derivatives.
abstract: New unsymmetrical [N2O2] tetradentate Schiff base complexes of Ni(II), Cu(II), Zn(II), and VO(II) were synthesized by template condensation of the tetradentate precursor 1-phenylbutane-1,3-dione mono-S-methylisothiosemicarbazone with o-hydroxybenzaldehyde or its 5-phenylazo derivative. They were characterized by elemental analysis, IR, UV-vis, electron spin resonance, and NMR spectroscopy, mass spectrometry, and magnetic measurements. The crystal structures of five of them have been determined by X-ray diffraction using, in some cases, synchrotron radiation. These compounds are characterized by a large thermal stability; their decomposition temperatures range from 240 up to 310 degrees C. Complexes with the phenylazo substituent were found to possess a large second-order nonlinear optical (NLO) response, as determined both by measurements of solution-phase direct current electric-field-induced second harmonic generation and by theoretical time-dependent density functional theory (TDDFT) calculations. The molecular hyperpolarizability was found to decrease in the order Zn(II) > Cu(II) > Ni(II) approximately VO(II). The active role of the metal in determining the NLO properties of the complexes was shown through an analysis of their UV-vis spectra, which revealed the presence of metal-to-ligand (in closed-shell complexes) and ligand-to-metal (in open-shell complexes) charge-transfer bands together with intra-ligand charge-transfer transitions. Assignment of the bands was based on the analysis of the TDDFT computed spectra.
authors.affiliation: Institute of Chemistry of the Academy of Sciences of Moldova, str. Academiei, 3, MD-2028 Chisinau, R. Moldova.
authors.forename: Julieta
authors.initials: J
authors.lastname: Gradinaru
authors.forename: Alessandra
authors.initials: A
authors.lastname: Forni
authors.forename: Vadim
authors.initials: V
authors.lastname: Druta
authors.forename: Francesca
authors.initials: F
authors.lastname: Tessore
authors.forename: Sandro
authors.initials: S
authors.lastname: Zecchin
authors.forename: Silvio
authors.initials: S
authors.lastname: Quici
authors.forename: Nicolae
authors.initials: N
authors.lastname: Garbalau