Theoretical study of dibenzotetraaza[14]annulene complexes with first row transition metals

The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (MII(DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M–N distance (d(M–N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M–N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO–LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving–Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.