Structural Particularities of Monodeprotonated Hemihexaphyrazine Complexes with Y, La, and Lu according to Quantum Chemical Calculations

The molecular structure of mononuclear noncentrosymmetric complexes of Y, La, and Lu with the ABABAB-type six-membered porphyrinoid hemihexaphyrazine H3Hhp of the composition MH2Hhp was studied using the DFT method. It was determined that the macrocyclic ligand of these complexes has a planar structure. The electronic density distribution in the MH2Hhp molecules was studied by QTAIM calculations and NBO analysis. It was shown that, in each complex, three coordination bonds are formed among the M atom and the nitrogen atom of the pyrrole fragment and two nitrogen atoms of the neighboring thiadiazole fragments. The H2Hhp ligand is quasi-tridentate, although the complexes MH2Hhp are formed by the substitution of only one hydrogen atom. It was demonstrated that the electronic structure of the complexes MH2Hhp is inconsistent with the conventional concepts of the oxidation states of the metal and the ligand in such structures (MI+H2HhpI–). Calculations by the TDDFT method determined that the electronic absorption spectra of the complexes MH2Hhp contain absorption bands in the IR region, and that the complexes can have pronounced donor properties.