Theoretical Study of Quinoline Aza Oxa Thia 17-Crown -6 Complexes: NICS Aromaticity
Esmael Rostami, Nosrat Daryapour, Roya Afsharpour
Complexation of quinoline aza oxa this 17-crown-6 (L) with some metal cations (K+, Na+, Li+, Mg2+) was studied through computational methods. Hartree-Fock method was employed to identify structure and thermodynamical binding constant of crown and metal ions complexes. The calculations were conducted at the HF/6-31g and HF/Lanl2DZ levels of theory. According to the obtained data Mg2+ ion formed the most stable complex with crown and equilibrium binding constants of complex formation has the following order: L. K+ < L. Na+ + 2+. In order to verify the physical properties of free crown and complexes some important physical properties including band gap, energy, hardness and dipole moments were obtained and discussed. The electron distribution over the free crown and its L. Mg2+ complex was studied which showed that in the free crown and its L. Mg2+ complex, Highest Occupied Molecular Orbital (HOMO) were distributed mainly over the sulfur atom. For both of them Lowest Unoccupied Molecular Orbital (LUMO) were distributed over aromatic rings. HOMO and LUMO orbitals in L. Mg2+ complex was not distributed over Mg2+ ion and the ion remained bare. Also, atomic charges and charge transfer between donors and acceptors were studied using natural bond orbital analysis (NBO). The charge of Mg2+ ion in the complex is 1.69095 e. In order to study the effect of complex formation and structural changes on the aromaticity of rings, Nuclear Independence Chemical Shift (NICS) and aromaticity were obtained and discussed.