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.