Synthesis and characterization of novel quinaldic acid based Ni, Fe, and Cr Complexes: A computational and experimental study

Complexes ([Ni(quin-2-c)2(H2O)2]•2H2O, [Fe(quin-2-c)2(H2O)2], [Cr(quin-2-c)2(H2O)2] were synthesized from aqueous solutions of metal salts, quinaldic acid, and semicarbazide. In the crystal structure of the first complex, the nickel atom is chelated by the deprotonated quinaldic acid molecule through the oxygen atom of the carboxyl group, and the heterocyclic nitrogen atom, as well as two water molecules, are coordinated. The other two water molecules are located in the outer sphere. In the structure of the iron and chromium complexes, the metal atoms have a similar complex formation but do not have water molecules in the outer sphere. In all compounds, quinaldic acid acts as a bidentate ligand to form five-membered metallocycles. The electronic structure properties were investigated through theoretical modeling using the B3LYP method at the 6–31 + G(d,p) computational level. Density functional theory (DFT) was employed in quantum chemistry simulations to refine proposed structures and explore the characteristics of frontier orbitals via analysis of frontier molecular orbitals (FMOs). These computations facilitated the identification of specific sites on the surface of molecules by generating molecular electrostatic potential maps and provided insights into the structural and reactive properties. Hirshfeld surface analysis was conducted to examine intermolecular interactions, revealing a prevalence of H⋅⋅⋅H interactions.