To Chemistry Journal Vol 4 (2019) ISSN: 2581-7507 http://purkh.com/index.php/tochem 25 Theoretical Study of Quinoline Aza Oxa Thia 17-Crown -6 Complexes: NICS Aromaticity Nosrat Daryapour,* Roya Afsharpour, Esmael Rostami * Department of chemistry, Payame Noor University, PO BOX 19395-3697 Tehran, Iran. e.rostami@pnu.ac.ir Abstract Complexation of quinoline aza oxa this 17-crown-6 (L) with some metal cations (K + , Na + , Li + , Mg 2+ ) 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 Mg 2+ ion formed the most stable complex with crown and equilibrium binding constants of complex formation has the following order: L. K + < L. Na + <L. Li + <L. Mg 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. Mg 2+ complex was studied which showed that in the free crown and its L. Mg 2+ 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. Mg 2+ complex was not distributed over Mg 2+ 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 Mg 2+ 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. Keywords Quinoline, Aza Oxa This 17–Crown–6, NICS (0) Aromaticity, Metal Ion Complex, Theoretical Study Introduction The first reported crown ethers were prepared by Pedersen in 1967 and their host-guest properties toward metal ions were identified [1]. The supramolecular properties of crown ethers were enhanced by several structural modifications such as application of softer donor atoms, especially nitrogen and sulfur in the cavity of crown ether [2], insertion of side chains (lariats) [3] in the crown ether structure and synthesis of three-dimensional macrocycles [4]. Supramolecular chemistry has been developed into new fields due to the mentioned changes in the macrocycles and similar structures as major building blocks of supramolecular assemblies [ 5-7]. In this content, plenty of applications have been explored for the wide range of macrocyclic architectures [8,9]. They have also played a significant role in the synthesis and study of challenging molecular architectures [10]. Self-assembly of macrocycles is an important tool for the construction of supramolecular arrays such as nanostructures [11]. In fact, construction of supramolecular systems occurs through host-guest or similar interactions [12]. In continuation of our researches on the synthesis and application of crown ethers and their derivatives [13], in this research computational study of metal ion complexation of 17-crown–6 containing quinoline was reported. Computational Methods Gaussian 09 software package was utilized to calculate the structures and properties of the system [14]. GussView 5 was also used to construct input files and observe the output files [15]. At first, a crown (L) was optimized using semi-empirical methods (PM6) and the frequency calculation shows that the first frequency mode is positive and there are no imaginary structures. Aza oxa thia crown structure and complexes were optimized using HF/6-31g and HF/Lanl2DZ levels of theory. DFT calculations led to the destruction of molecules,