Exploring the potential of novel transition metal complexes derived from ONO donor type ligand: a quantum chemical...

In the present quantum chemical investigation, we predict several novel transition metal complexes which are designed using tridentate ONO donor type Schiff base ligand (2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene) amino) phenol). The stable molecular geometries of newly designed metal complexes are obtained using density functional theory (DFT) methods. Several properties including geometrical parameters, energies of frontier molecular orbitals (FMOs), and interaction energies are calculated for optimized metal complexes. The more negative interaction energies illustrate more susceptibilities of the reaction of metal cations with ligand. The charge transfers from ligand to metals are observed in the d⁷ and d⁸ metal complexes while it is seen as backdonation of charge from metal to ligand in the d¹⁰ complexes. The quantum chemical characterizations are performed for calculating UV-visible spectra and IR frequencies for all the designed metal complexes. All designed metal complexes show multiple absorption peaks in UV region ranging from 184 to 376 nm, which are related to metal to ligand and ligand to metal charge transfer processes. The IR frequency analysis shows that the -C=N- stretching frequency of ligand in the region of 1650-1580 cm^-1 is decreased by between 50 and 100 cm^-1, which may assign the coordination of ligand with metal via nitrogen. Moreover, the investigations of nonlinear optical (NLO) polarizabilities among selected complexes show that these complexes may possess good potential for NLO applications. The most interesting results are found about the third-order NLO polarizabilities (γ_||) where the γ_|| amplitudes are found to be 60.01 × 10^-36, 56.48 × 10^-36, 90.04 × 10^-36, and 64.57 × 10^-36 esu for complexes 1, 2, 9, and 10, respectively. Thus, we believe that the present investigation may bring the newly designed metal complexes in the limelight of scientific interest for their practical realization in optical and nonlinear optical applications. Graphical abstract Several novel transition metal complexes are designed using tridentate ONO donor type Schiff base ligand as efficient NLO materials.