H-type aggregation of functional metal ion sensing phthalocyanines: Synthesis, characterization and electrochemistry

Abstract

We report, in this study, the preparation and physical characterization of the peripherally functionalized ionophore ligand, 4,5-bis(6-hydroxyhexan-3ylthio)-1,2-dicyanobenzene ( 1) and its branched thioalcohol-substituted phthalocyanines, 2,3,7,8,12,13,17,18-octakis{6-hydroxyhexan-3-ylthio)-metal (II) or (III) phthalocyanines {M{Pc[SCH(C 3H 7)(C 2H 5OH)] 8} {M = Pb(II) ( 2), Zn(II) ( 3), Cu(II) ( 4), Co(II) ( 5) and Mn(III), X = Cl − ( 6)} which can selectively bind soft-metal ions such as silver (I) and palladium (II). It was observed by means of UV–Vis absorption spectrophotometry that the aggregates formed lead to a low solubility of the phthalocyanines in protic solvents, such as low molecular alcohols. However, the addition of AgNO 3 and Na 2PdCl 4 into a THF–MeOH solution of {M{Pc[SCH(C 3H 7)(C 2H 5OH)] 8X} {M = Pb(II) ( 2), Zn(II) ( 3), Cu(II) ( 4), Co(II) ( 5) and Mn(III), X = Cl − ( 6)} induced optical changes, which indicated the formation of twisted H-type dimers (blue shift, face-to-face fashion) of {M{Pc[SCH(C 3H 7)(C 2H 5OH)] 8} complexes, bound by four PdCl 2 and AgNO 3 units in THF solution. Elemental analysis data, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/MS), FT-IR, 1H, 13C NMR, and UV–Vis spectral data were used as complementary techniques. Voltammetry and in situ spectroelectrochemistry of the complexes were performed on Pt in DMSO/TBAP. The first reduction and oxidation processes of 5 were found to be split due to the presence of facile equilibria between the species coordinated differently at axial positions. The Mn(III)Pc(−2)X − complex ( 6) displayed well-defined colour changes during its reduction processes. The redox behaviour of the Mn(III)Pc(−2)X − complex was observed to be affected significantly by the existence of oxygen in solution due to the formation of μ-oxo MnPc species, Mn(III)Pc–O–PcMn(III). This effect was clarified well by in situ spectroelectrochemical measurements.