The static and frequency-dependent second- and third-order nonlinear optical properties of Zn(II) and Ni(II) complexes of 4-methoxypyridine-2-carboxylic acid: A detailed experimental and theoretical study

Novel Zn(II) and Ni(II) complexes, [Zn(MeOPic)(2)(H2O)(2)] and [Ni(MeOPic)(2)(H2O)(2)] (MeOHPic = 4-methoxypyridine-2-carboxylic acid [4meOHPic]), have been prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet-visible (UV-Vis) techniques. Crystal structure analysis demonstrated that the 4meOHPic ligand is coordinated as a two-dentate ligand through N and O atoms to central metal ions, and both of the complexes have distorted octahedral coordination geometry. The DFT-B3LYP/6-311++G(d,p)/LanL2DZ level was executed to perform DFT calculations for the Zn(II) complex with singlet spin state and the Ni(II) complex with triplet spin state. The UV-Vis electronic absorption spectra and natural bonding orbital (NBO) analyses also demonstrated that ligand-ligand and metal-ligand charge transfer interactions occur in Zn(II) and Ni(II) complexes. However, static and frequency-dependent first-order hyperpolarizability (& beta;) parameters were found to be low because of the centrosymmetric crystal structures. As for the second-order hyperpolarizabilities, the quadratic electro-optical Kerr effect & gamma; (-& omega;;& omega;,0,0) and electric field induced second harmonic generation & gamma; (-2 & omega;;& omega;,& omega;,0) parameters were calculated as 13.04 x 10(-36) and 2258.9 x 10(-36) esu for Ni(II) complex. Accordingly, it was demonstrated that Ni(II) complex is a potential candidate for third-order nonlinear optical (NLO) materials.

Automated summary

Novel Zn(II) and Ni(II) complexes were synthesized and characterized. XRD, FTIR, and UV-Vis techniques confirmed the coordination of 4-methoxypyridine-2-carboxylic acid (4meOHPic) ligand to the metal ions. DFT calculations revealed the singlet spin state of the Zn(II) complex and the triplet spin state of the Ni(II) complex. The UV-Vis spectra and NBO analysis indicated charge transfer interactions in both complexes. The Ni(II) complex showed potential as a third-order nonlinear optical material.