Complexation of Ni(ClO4)2 and Mg(ClO4)2 with 3-hydroxyflavone in acetonitrile medium: conductometric, spectroscopic, and quantum chemical investigation.

The complex formation of Ni(ClO4)2 and Mg(ClO4)2 with 3-hydroxyflavone (HL, flavonol) in acetonitrile was studied using conductometric and spectroscopic methods. It was found that interaction of nickel cation with HL leads to formation of the doubly charged [Ni(HL)](2+) complex, whereas in solutions of magnesium perchlorate the complex with anion [MgClO4(HL)](+) is formed. Using the extended Lee-Wheaton equation, the limiting equivalent conductivities of [Ni(HL)](2+) and [MgClO4(HL)](+) and thermodynamic constants of their formation were obtained at 288, 298, 308, 318, and 328 K. Calculated Stoke's radii indicate weak solvation of the formed complexes and low temperature stability of their solvation shells. On the basis of the quantum chemical calculations and noncovalent interactions analysis, it is found that in the solvated [Ni(HL)](2+) and [MgClO4(HL)](+) complexes interaction of the Ni(2+) and Mg(2+) cations with flavonol occurs via the carbonyl group of HL. Complexation with Ni(2+) does not change the internal structure of HL greatly: in the [Ni(HL)](2+) complex, flavonol shows an intramolecular H-bond between 3-hydroxyl and carbonyl groups. When a complex with [MgClO4](+) is formed, the OH group turns out of the plane of the chromone moiety that leads to rupture of an intramolecular H-bond in the ligand molecule. Moreover, in the [MgClO4(HL)](+) complex, perchlorate anion possesses a strong ability to interact with HL, forming an intracomplex H-bond between hydrogen of the 3-hydroxyl group and oxygen of ClO4(-). Its strength is more pronounced than in the intramolecular one in both [Ni(HL)](2+) and uncomplexed 3-hydroxyflavone.