Synthesis, crystal structures, and DFT calculations: novel Mn(II), Co(II) and Ni(II) complexes of N?(pyridin?2?ylmethylene)methanamine with isothiocyanate as promising optical materials

To investigate the optical parameters, novel metal complexes of N-(pyridin-2-ylmethylene) methanamine ( L1), obtained as Schiff base by the condensation reaction of 2-pyridinecarboxaldehyde with methylamine, and isothiocyanate {[Mn(L1)2(NCS)2], (1), [Co(L1)2(NCS)2], (2), [Ni(L1)2(NCS)2], (3)} were synthesized. FT–IR and UV–Vis spectra were applied to examine the spectral features for complexes 1,2/3 characterized by XRD/ LC-HRMS. Hirshfeld surface analysis was performed to describe intermolecular interactions for complexes 1 and 2. Moreover, the CAM-B3LYP and ?B97XD/6–311 + G(d,p)// LanL2DZ levels of DFT/TD-DFT methods were used to survey optimal complex structures, spectral and nonlinear optical parameters, as well as remarkable contributions in the electronic transitions for synthesized complexes 1–3. In the mid-IR region, the mean refractive index/polarizability parameters for 1–3 were found to be 1.63/5.87 × 10– 24 esu, 1.46/4.80 × 10– 24 esu, and 1.50/4.48 × 10– 24 esu, respectively. By considering the UV–Vis absorption parameters, the experimental refractive index, optical band gap, polarizability, optical conductivity, and third-order nonlinear optical susceptibility parameters for complexes 1–3 in methanol were examined. The maximum third-order NLO susceptibility values in the photon energies of 4.68, 4.21, and 5.25 eV were obtained at 51.65 × 10– 13, 51.42 × 10– 13, and 51.42 × 10– 13 esu, respectively. In short, detailed experimental and corresponding theoretical spectral and optical parameters for the synthesized complexes were investigated in terms of structure–property. The NLO results display that complex 1 may be a candidate for NLO material using in data storage, telecommunications, laser technology, etc. sectors in the future.