Rectangular-Shaped Expanded Phthalocyanines with Two Central Metal Atoms

Expanded phthalocyanine (Pc) congeners with two Mo or W central metal ions and four isoindole ring moieties have been synthesized using normal Pc formation conditions in the presence of urea. The products have been characterized by electrochemistry; mass spectrometry (MS); IR, electron paramagnetic resonance (EPR), NMR, electronic absorption, and magnetic circular dichroism (MCD) spectroscopies; and X-ray analysis. The X-ray structures have rectangular C_2v symmetry and provide evidence that the central Mo atoms are linked by a single bond and coordinated by two isoindole nitrogen atoms and two nitrogen atoms from the amine moieties. The electronic absorption bands extend into the 1200–1500 nm region. This can be explained using Gouterman’s four-orbital theory. The experimental NMR data and theoretical calculations provide evidence for a heteroaromatic 22-π-electron conjugation system for the ring-expanded Pc system, which satisfies Hückel’s (4n + 2)­π aromaticity.