A comparative study of reactivity of μ-nitridoand μ-oxo-dimers of iron tetrasulfophthalocyanine has been performed in aqueous solutions of various acidity. The substantially higher stability of the nitrido-bridged structure under both strongly acidic and strongly alkaline environments was demonstrated. The reactions of the complexes with sulfur-containing reductants (sodium dithionite, thiourea dioxide, sodium hydroxymethanesulfinate, L-cysteine) were studied. Differences in reduction processes were explained.