ChemInform Abstract: Acidity and Dimerization of Three Water‐Soluble Iron(III) Porphyrin Cations: (meso‐α,β,α,β‐Tetrakis(o‐(N‐methylnicotinamido)phenyl)por# phyrinato)iron(III), (meso‐α,α,α,α‐Tetrakis(o‐(N‐methylnicotinamido)phenyl)p# orphyrinato)iron(III), and (meso‐Tetrakis(1‐methylpyridinium‐4‐yl)porphyrinato)iron(III).

Abstract Acidity data for the monomeric diaquo title porphyrins having both sides of the macrocyclic plane restricted toward further coordination (substituents in α‐ and β‐position) or one face restricted (substituents only in α‐position) or having both faces open toward coordination by a fifth and sixth ligand are determined by spectrophotometric titration.