DFT studies of ONO Schiff bases, their anions and diorganotin(IV) complexes: Tautomerism, NBO and AIM analysis

The geometry of three tautomeric forms of three ONO Schiff bases, H2La = 3-(3-hydroxypyridin-2-ylamino)-1-phenylbutan-1-one, H2Lb = 3-(2-hydroxy-5-methylphenylamino)-1,3-diphenylprop-2-en-1-one, H2Lc = 4-(2-hydroxynaphthalen-3-ylamino)pent-3-en-2-one, their dianions (L2−) and diorganotin(IV) complexes (Me2SnLa, Me2SnLb and Ph2SnLc) are optimized at B3LYP/6-311+G** level of theory for all atoms and B3LYP/DZVP for the Sn. In agreement with experimental data, in all systems, the preferred tautomer of Schiff bases is the keto-amine form according to energy parameters (E, ΔH and ΔG). Also, the electronic structure of complexes and dianions are investigated in terms of AIM topological analysis of electron density and Natural Bond Orbitals (NBOs). The electron density, ρ, its Laplacian, L, and bond ellipticity, ε, at bond critical points (BCPs) as well as atomic volumes and atomic charges calculated using the electron density integrated over atomic basins are correlated with different π bonding in complex and mechanical strain data. According to AIM methodology, all metal-ligand bonding have positive ∇2ρBCP values in agreement with their coordination (non-sharing) bonding character.