Abstract
Gold(III) coordination compounds with three water-soluble porphyrins―5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TSPP4–), 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP4+), and 5,10,15,20-tetrakis(4-N,N,N-trimethylaminophenyl)porphyrin (H2TTMAPP4+)―have been studied. Complex [Au(TTMAPP)]5+ has been prepared for the first time. The analysis of coordination-induced shifts of proton signals in NMR spectra and intensities of Q bands in absorption spectra indicates the high degree of bond covalence in the studied metal porphyrins and a partial transfer of electron density from porphyrin to gold ion. The cationic complexes [Au(TMPyP)]5+ and [Au(TTMAPP)]5+ in aqueous solutions has been found to exist in monomeric form, while anionic complex [Au(TSPP)]3– undergoes dimerization upon growth of concentration and solution ionic strength. Equilibrium constant for dimerization has been calculated, the constant has been found to decrease when temperature rises. Thermodynamic parameters of dimerization process have been determined: ΔH° =–31.8 kJ/mol and ΔS° =–13.8 J/mol K.
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