<p>DFT calculations using BP86, PBE, and B3LYP functionals have been carried out on a series of complexes of the types [M(L1)(L2)]²⁺, [M(L2)₂]²⁺, [M(L2)(L3)₂]²⁺, and [M((L3)₄]²⁺ (M = Ni, Pd, Cu, Zn, and L1 = N-(4methoxybenzylidene) isonicotihydrazone bidentate Schiff base, L2 = 2,2′-bipyridine, and L3 = pyridine). A complete rationalization of bonding is provided of these kinds of complexes, where the predicted structures provide to the M(II) cations a perfect square planar geometry for Ni(II), Pd(II), and Cu(II) and a tetrahedral one for Zn(II). Large HOMO–LUMO gaps are calculated for all optimized structures of singlet spin state except for Cu(II) with a doublet spin state; suggesting a good kinetic stability. The low singlet spin state for Ni(II), Pd(II), and Zn(II) and the doublet spin state for Cu(II) complexes are characterized by BP86, PBE, and B3LYP functionals as ground states compared to those of high triplet and quartet spin ones, respectively. The TD-DFT theoretical study performed on the optimized geometries permitted us to predict the UV–Vis spectra and to pinpoint accurately the spectral positions and the nature of the different electronic transitions according to their molecular orbital localization; hence, the available experimental UV–Vis spectra are compared to our findings. The electronic spectra obtained in ethanol solvent show red shifts for complexed species due to the coordination of free ligands with metal cations characterized by HOMO → LUMO and HOMO-1 → LUMO electronic transitions.</p>