The axial coordination in subphthalocyanines: Geometrical and electronic aspects

Abstract

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.

Structural Modulation of the Dipolar−Octupolar Contributions to the NLO Response in Subphthalocyanines

“…This demonstrates that, in our case, the electron-withdrawing process is mostly inductive in nature since theoretical and experimental studies have shown that the B-Cl distance is correlated to the electron donor/acceptor properties of the peripheral substituents. 35 The most significant structural difference among the series lies, not surprisingly, in the relative orientation of the nitro group with respect to the plane of the adjacent phenyl ring. 36, 37 In the meta isomers 1 and 2 the nitro groups are coplanar to the phenyl ring whereas in the ortho isomers 3 and 4 the nitro groups are twisted ca.…”

“…It was previously demonstrated that, likewise, they do not depend on the nature of both the peripheral and the axial substituents. 35 Thus, it may be considered as a geometrical constant that characterizes the rigid core of the subphthalocyanines. Also, it is interesting to note that the B-Cl bond distance remains invariable for all the studied compounds (Table 1).…”

Density functional study of the redox processes in subphthalocyanines

“…Oxidation and reduction give rise to the lengthening and shortening, respectively, of the BCl bond length. A possible broad explanation for this fact is that the addition of one or more electrons increases the electron density in the macrocycle (because the redox processes in SubPc mainly involve the macrocycle but not the Cl axial substituent 19–21) and, consequently, leads to an increase of the repulsion between the Cl atom and the macrocycle that are both negatively charged. Because Δ d /Δ d and Δ d /Δ d are less than 2, it can be concluded that these repulsive effects are not additive.…”

“…This may be explained taking into account that the reductive electrons are mostly located in the macrocycle as suggested by the spatial distribution of the LUMOs (see Refs. 19–21).…”

“…Redox reactions in both porphyrins and phthalocyanines are known to take place at both the central metal (in particular when that is a transition metal) and at the conjugated macrocycle levels 18. In the case of SubPcs, it was suggested 3, 4, 19–21 that redox reactions involve the SubPc macrocycle but do not involve the central boron (which is in a saturated valence state). More recent calculations indicate that peripheral substituents on the SubPc macrocycle may also participate in the redox processes 20.…”