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-tetracy ano-3,5-dihydro-3,5-diiminopyrrolizinide (L) and the 2,4-tert-butylacetylac etonide (DPM) ligands have been synthesized and characterized. The absorpti on 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 l ow-energy spectral region where the first pi-->pi* transitions occur (Q ban d). The Q band position of the pyrrolizinato complexes is much more dependa nt on the metal than is the case for MPc. For the same metal, the Q band po sition is also dependant on the M-N bond lengths in the molecular plane. Fo r 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 pyridi ne solvate NiL(DPM)(Pyr)(2) . 2 Pyr and on their solvatochromism. A symmetr y-based correlation diagram between the frontier orbitals of the pyrrolizin ato-complexes and the phthalocyanines is proposed.