The fascinating story of axial ligand dependent spectroscopy and redox-properties in iron(II) phthalocyanines

Tuning the visible colour of octahedral manganese(III) phthalocyanines via axial ligand exchange

A series of [PcMnL2]SbF6 complexes (Pc = phthalocyanine) was synthesized and structurally characterized by stripping the chloride from PcMnCl with AgSbF6 in o-dichlorobenzene and adding a range of donor ligands (L = THF, pyridine, p-dimethylaminopyridine (DMAP), Ph3PO, N-methylimidazole (MeIm), MeCN) to the resulting solution. Addition of or exposure to water where L = heterocyclic amines yielded μ-oxo complexes of the form [PcMnL]2O, which were structurally characterized for L = DMAP and MeIm. The [PcMnL2]SbF6 complexes have an increased solubility in organic solvents, where the axial ligands inhibit the characteristic ring π-π aggregation of PcM complexes. A variety of colours were observed (blue/green to red/purple), with Q-band absorptions (excluding the μ-oxo species) spanning from 715-761 nm and LMCT-bands from 497-574 nm. The combination of the ligand-induced absorption shifts coupled with their relative intensities in the visible region is responsible for the observed colour range and illustrates that facile ligand exchange is a useful tool in producing materials with a variety of colours from PcMnCl.