Synthesis and spectral properties of a dihydroxo(phthalocyaninato)antimony(V) complex

Abstract

The title complex cation, [ Sb ( pc )( OH )2]+, (pc = phthalocyaninate, C 32 H 16 N 82-) has been prepared by oxidizing [ Sb ( pc )] I 3 with tert-butyl perbenzoate and isolated as hexafluorophosphate and triflate salts. These salts are relatively well-soluble in polar solvents (e.g. CH 2 Cl 2, acetonitrile, acetone) without detectable aggregation. In particular, they dissolve relatively well in ethanol and methanol in which [ Sb ( pc ) Br 2]+ or [ Sb ( pc ) Cl 2]+ salts are poorly soluble whereas they have extremely low solubility in 1-chloronaphthalene and CHCl 3, unlike the bromo or chloro analogs. The spectral properties of [ Sb ( pc )( OH )2]+ have been investigated by optical absorption and magnetic circular dichroism spectroscopy. Although its Q band tends to appear at a longer wavelength in a solvent with a larger refractive index, as is the case for its Br and Cl analogs, the Q band positions in donor solvents deviate considerably from linear correlation between Onsager's solvent polarity function. In the Soret band region, spectra of [ Sb ( pc )( OH )2]+ are different in CH 2 Cl 2 and acetonitrile, particularly around the B1/B2 bands, unlike the bromo and chloro analogs. The solvent dependence of absorption spectra and the difference in solubility suggests that the presence of the axial hydroxyl groups endows the phthalocyanine macrocycle with considerable hydrophilicity. It also suggests that there are some specific chemical interactions between the axial hydroxyl groups and the surrounding donor solvent molecules.