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.

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

“…By comparing the results of HS and LS states of these complexes, we note a strong increase in the dipole moment [β­(0; 0,0), β­(−ω; ω,0) and β­(−2ω; ω,ω)] on going from LS (singlet) to HS (triplet), excepted in the case of β HRS (static and dynamic) and β­(−2ω;ω,ω) for the NiL 1 and PdL 1 complexes. Generally, these results show that open-shell complexes have larger values of second-order NLO parameters compared with the corresponding closed-shell ones (see Table S10). The DFT calculation indicates that the spin state of complexes plays an important role in determining the NLO parameters.…”

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

“…By comparing the results of HS and LS states of these complexes, we note a strong increase in the dipole moment [β­(0; 0,0), β­(−ω; ω,0) and β­(−2ω; ω,ω)] on going from LS (singlet) to HS (triplet), excepted in the case of β HRS (static and dynamic) and β­(−2ω;ω,ω) for the NiL 1 and PdL 1 complexes. Generally, these results show that open-shell complexes have larger values of second-order NLO parameters compared with the corresponding closed-shell ones (see Table S10). The DFT calculation indicates that the spin state of complexes plays an important role in determining the NLO parameters.…”

Dipolar Copper(I) Complexes: A Novel Appealing Class of Highly Active Second-Order NLO-Phores

“…The EFISH μβ values of complexes 1 – 4 , measured as solutions in CHCl 3 , are shown in Table 1 . They are in the range of 957–1100 × 10 −48 esu, much higher than that of Disperse Red One and of that previously reported for more laborious Cu(II) complexes, determined under the same conditions with an incident wavelength of 1907 nm [ 64 , 65 ] ( Scheme 3 ).…”

A study of structural effects on linear and nonlinear response of bicompartmental Ni (II) Schiff base complexes

“…The values for different parameters like electric dipole moment (μ), polarizability (α) and first hyperpolarizability (β hyp ) for all the compounds were computed at M06/6‐31G* level of theory (Table ). As expected from the experimental and energy gap calculations, the value for the first hyperpolarizability (β hyp ) is the largest for 5 (44.05 × 10 −30 esu) which is much higher than the similar reference Ni (II)salen compound (Figure S12, 11.93 × 10 −30 esu) computed at the similar level of theory . This unusual activity shown by 5 can be credited to the extensive π‐delocalization present in it which translates into a large molecular nonlinear response.…”

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

“…By comparing the results of HS and LS states of these complexes, we note a strong increase in the dipole moment [β­(0; 0,0), β­(−ω; ω,0) and β­(−2ω; ω,ω)] on going from LS (singlet) to HS (triplet), excepted in the case of β HRS (static and dynamic) and β­(−2ω;ω,ω) for the NiL 1 and PdL 1 complexes. Generally, these results show that open-shell complexes have larger values of second-order NLO parameters compared with the corresponding closed-shell ones (see Table S10). The DFT calculation indicates that the spin state of complexes plays an important role in determining the NLO parameters.…”

Dipolar Copper(I) Complexes: A Novel Appealing Class of Highly Active Second-Order NLO-Phores

“…The EFISH μβ values of complexes 1 – 4 , measured as solutions in CHCl 3 , are shown in Table 1 . They are in the range of 957–1100 × 10 −48 esu, much higher than that of Disperse Red One and of that previously reported for more laborious Cu(II) complexes, determined under the same conditions with an incident wavelength of 1907 nm [ 64 , 65 ] ( Scheme 3 ).…”

A study of structural effects on linear and nonlinear response of bicompartmental Ni (II) Schiff base complexes

“…The values for different parameters like electric dipole moment (μ), polarizability (α) and first hyperpolarizability (β hyp ) for all the compounds were computed at M06/6‐31G* level of theory (Table ). As expected from the experimental and energy gap calculations, the value for the first hyperpolarizability (β hyp ) is the largest for 5 (44.05 × 10 −30 esu) which is much higher than the similar reference Ni (II)salen compound (Figure S12, 11.93 × 10 −30 esu) computed at the similar level of theory . This unusual activity shown by 5 can be credited to the extensive π‐delocalization present in it which translates into a large molecular nonlinear response.…”

Correlation between Second Ionization Potential and Nonlinear Optical Properties of Bivalent Transition-Metal Complexes: A Quantum Chemical Study

“…By comparing the results of HS and LS states of these complexes, we note a strong increase in the dipole moment [β­(0; 0,0), β­(−ω; ω,0) and β­(−2ω; ω,ω)] on going from LS (singlet) to HS (triplet), excepted in the case of β HRS (static and dynamic) and β­(−2ω;ω,ω) for the NiL 1 and PdL 1 complexes. Generally, these results show that open-shell complexes have larger values of second-order NLO parameters compared with the corresponding closed-shell ones (see Table S10). The DFT calculation indicates that the spin state of complexes plays an important role in determining the NLO parameters.…”

Dipolar Copper(I) Complexes: A Novel Appealing Class of Highly Active Second-Order NLO-Phores

“…The EFISH μβ values of complexes 1 – 4 , measured as solutions in CHCl 3 , are shown in Table 1 . They are in the range of 957–1100 × 10 −48 esu, much higher than that of Disperse Red One and of that previously reported for more laborious Cu(II) complexes, determined under the same conditions with an incident wavelength of 1907 nm [ 64 , 65 ] ( Scheme 3 ).…”

A study of structural effects on linear and nonlinear response of bicompartmental Ni (II) Schiff base complexes

“…The values for different parameters like electric dipole moment (μ), polarizability (α) and first hyperpolarizability (β hyp ) for all the compounds were computed at M06/6‐31G* level of theory (Table ). As expected from the experimental and energy gap calculations, the value for the first hyperpolarizability (β hyp ) is the largest for 5 (44.05 × 10 −30 esu) which is much higher than the similar reference Ni (II)salen compound (Figure S12, 11.93 × 10 −30 esu) computed at the similar level of theory . This unusual activity shown by 5 can be credited to the extensive π‐delocalization present in it which translates into a large molecular nonlinear response.…”