Theoretical insight to the complexation of some transition metals with cryptand

The most practicable complexes formed between Cryptand[2.2.2] and hydrated Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) cations (denoted as [ML](+2)) were modeled using computational chemistry methods. The energies of complexation reactions were calculated in both gas phase and solution at B3LYP/6-31+G(d) and B3LYP/6-311++G(3df,2pd) levels of theory. The accuracy of selected computational methods was confirmed with comparison between available X-ray data and computational results. The results suggested that [CuL](+2) and [CoL](+2) structures could be the most and the least stable systems, respectively. The nature of metal-ligand interactions based on quantum theory of atoms in molecule (QTAIM) was discussed for all the complexes. This analysis confirmed the ionic nature of metal-ligand interactions due to electron density values for M-O bonds and M-N interactions. Natural bond orbital (NBO) and natural energy decomposition analysis (NEDA) were utilized to explain more details of interaction between divalent cations and donor atoms of the ligand.