First- and second-row transition metal oxa-aza macrocyclic complexes: a DFT study of an octahedral conformation.

A theoretical study of structures of the 1,7,1 l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20]AneN(4)O(4)) coordinated to Fe(2+), Co(2+), Ni(2+), Ru(2+), Rh(2+), and Pd(2+) transition metals ions was carried out with the DFT/B3LYP method. Complexes were fully optimized in C(s) symmetry with the metal ions coordinated either to nitrogen (1a) or oxygen atoms (1b). For all the cases performed in this work, 1a was always more stable than 1b. Considering each row it is possible to see that the binding energy increases with the atomic number. The M(2+) cation binding energies increase in the following order: Fe(2+)<Ru(2+)<Co(2+)<Ni(2+)<Rh(2+)<Pd(2+). In addition, it was observed the preference of Pd(2+) and Rh(2+) complexes for a tetrahedral arrangement, while Fe(2+), Ru(2+), Co(2+), Ni(2+) complexes had a preference for the octahedral arrangement. From the orbital representation results, it was seen that 1b unsymmetrical orbitals may influence the susceptibility over metal ions orientation toward heteroatoms orbitals.