Complexes of iron(III) with cyclopropanecarbo- and cyclohexyl-acetohydroxamic acids

Summary Cyclopropanecarbohydroxamic acid (CPAH) and cyclohexylacetohydroxamic acid (CHAH) were synthesized, characterized and their pK_a's determined spectro-photometrically as 9.80 and 9.85, respectively, at 25 °C and in buffers of 0.1 mol dm^–3 ionic strength (I). A spectroscopic investigation of their reactions with Fe^III in aqueous solutions revealed the sole formation of the 1:3 complexes at equilibrium. Stability constants (log ₃ at 25 °C and I = 0.1 mol dm^–3 are 34.80 and 34.22 for [Fe(CPA)₃] and [Fe(CHA)₃], respectively. Spectral and magnetic studies of the isolated complexes indicate octahedral coordination via the O atoms of the hydroxamate group.