engleski

Metal Cation Complexation by Polypyridine Macrocyclic Compounds

It is well known that macrocyclic compounds have ability to form stable complexes with metal ions of appropriate dimensions. The cavity size, the shape, the rigidity and the nature of the binding sites govern the binding power of the host. The cation possessing the "best fit" for the cavity in question will have the largest complexation energy. Therefore, the macrocycles can be potentially used for the separation of the specific metal ions [1]. Very interesting macrocyclic structures are provided by systems containing polypiridine building fragments [2]. The binding ability of metal cations is enabled through the interaction with the lone electron pairs of the nitrogen atoms. In the present work we have considered complexation of Li+, Na+, Be2+ and Mg2+ metal cations with system containing four pyridine subunits substituted in para position (R=H, NMe2)both in the gas phase and in acetonitrile solution. Gas phase molecular structures and complexation energies were calculated by the B3LYP/6-311+G(3df, 2p)//B3LYP/6-31G(d) method including basis set superposition error (BSSE) calculated by counterpoise (CP) correction scheme at the same level of theory. The solvent effects were assessed using the polarized continuum method (PCM). It is found that Be2+cation has the largest interaction energy in investigated system. The corresponding gas phase binding enthalpies are -521.6 kcal mol-1 (R=H) and -553.8 kcal mol-1 (R=NMe2). The log K values in acetonitrile are 46.7 and 58.3 units, respectively. [1] R. M. Izatt, K. Pawlak, J. S. Bradshaw and R. L. Bruening, Chem. Rev., 1991, 91, 1721. [2] I. Despotović, B. Kovačević and Z. B. Maksić, New. J. Chem., 2007, 31, 447

macrocyclic compound; complexation; metal cation

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