On the spectral similarities between 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinato complexes and phthalocyanines - X-ray crystal and molecular structure of two mixed monopyrrolizinato nickel(II) complexes with the 2,4-tert-butylacetglacetoaide ligand

Complexes of Ni-II, Cu-II, Zn-II, and Co-III containing the 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinide (L) and the 2,4-tert-butylacetylacetonide (DPM) ligands have been synthesized and characterized. The absorption optical spectra of these species and of the corresponding ML2 complexes in coordinating solvents are compared with those of metal-phthalocyanines (MPc) and hydrogen-phthalocyanine (H2Pc), respectively. The comparison shows a close similarity, especially for the nickel-containing species, in the low-energy spectral region where the first pi-->pi* transitions occur (Q band). The Q band position of the pyrrolizinato complexes is much more dependant on the metal than is the case for MPc. For the same metal, the Q band position is also dependant on the M-N bond lengths in the molecular plane. For M = Ni, a reduction of this distance causes a red-shift of the Q band and a decrease of its maximum intensity. These conclusions are based on the X-ray molecular structure of the solvent-free NiL(DPM) complex and its pyridine solvate NiL(DPM)(Pyr)(2) . 2 Pyr and on their solvatochromism. A symmetry-based correlation diagram between the frontier orbitals of the pyrrolizinato-complexes and the phthalocyanines is proposed