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.

Mono and dinuclear half-sandwich platinum group metal complexes bearing pyrazolyl-pyrimidine ligands: Syntheses and structural studies

“…In many cases the charge transfer properties of these compounds justify this interest. Especially with these nitrogen donor ligands have been shown to be effective catalysts for oxidation reactions [11][12][13][14][15][16][17][18][19] and for ringopening metathesis polymerization [20] and recent studies of arene ruthenium complexes have shown that they are found to inhibit cancer cell growth [21][22][23][24][25][26], as non-linear optical (NLO) materials [27,28]. For a majority of the complexes studied, the metal centers are linked by a bridging ligand and the nature of the bridge has a fundamental influence on the electronic interaction between the metals and therefore on the characteristics of the material.…”

Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

“…[4] Of particular interest are salen ligands functionalized by an electron-donor (D)/electron-acceptor (A) pair having intramolecular charge-transfer (ICT) properties, such that the associated complexes may have nonlinear optical (NLO) properties. [5,6] To enhance the strength of ICT, the salen ligands are generally anchored by a strongly electron withdrawing moiety such as a cyano group (A) on diamines and dialkylamino substituents (D) at the conjugated position of the diamines. Such D-A-D conjugated structures have attracted much attention due to their characteristic electronic and optical properties.…”

A new hybrid DFT approach to electronic excitation and first hyperpolarizabilities of transition metal complexes

“…2, 3,5,[7][8][9][10] The existence of TM atoms in the organometallic complexes give rise to the special metal-ligand bonding interaction and could result in the different NLO response behavior when compared with the more thoroughly investigated metalfree organic molecules. The previous studies have shown the importance of the CT between the TM atom and the ligands.…”

“…1): tungsten pentacarbonyl pyridine W(CO) 5 Py (1), tungsten pentacarbonyl derivative with extensive p-delocalization pyridine ligand W(CO) 5 PyCHO (2), and chromium tricarbonyl arene complex Cr(CO) 3 Bz (Bz denotes benzene) (3). They are the typical organometallic carbonyl complexes with the second-order NLO responses that are mostly investigated so far.…”