The axial coordination in subphthalocyanines.: Geometrical and electronic aspects

Theoretical calculations were performed for studying the electronic molecular structure of axial subphthalocyanine (SubPc) derivatives. The intermolecular SubPc interactions were also investigated at theoretical level using adequate models. These models represent the interaction of one Cl(OR)-SubPc with the surrounding molecules through the Cl atom as well as the interaction of the Cl-SubPc with an incoming diiminoisoindole group in the first steps of the open ring reaction. The SubPc complexes with more electronegative atoms than Cl heteroatoms in apical positions are more pyramidal than Cl-SubPc. The B-X and B-Np are the most sensitive macrocycle positions with respect to the axial substitutions in SubPcs. The B-X bond has an elevated polarity and seems to correlate with the chemical reactivity of these compounds. The theoretical calculations of the near-frontier orbitals reveal an outstanding energetic and structural homogeneity along the studied series which is in correspondence with the fact that the axial ligand has only a small influence on the position of the maximum bands in UV-vis spectra as well as in the first half-wave potentials for oxidative processes. The study of the intermolecular interactions give information about their influence on the molecular structure of the axial complexes of the SubPcs. The characterization of the interaction of one Cl-SubPc with a pyrrol containing group may be useful in the understanding of the mechanism of the ring expansion reactions. In general, the present results indicate that the apical position may be a critical reactive center both for redox and axial substitution processes. Copyright (C) 2001 John Wiley & Sons, Ltd.