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 (β) parameters were found to be low because of the centrosymmetric crystal structures. As for the second‐order hyperpolarizabilities, the quadratic electro‐optical Kerr effect γ (−ω;ω,0,0) and electric field induced second harmonic generation γ (−2ω;ω,ω,0) parameters were calculated as 13.04 × 10−36 and 2258.9 × 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. [ABSTRACT FROM AUTHOR]