In weakly coordinating solvents Fe^II meso-(N-methylimidazol-2-yl)porphine 1Fe exists as a stable dimer (K_d = 50 ± 30 nM) that binds ligands without undergoing dissociation and is presently the simplest complex in which the mono-imidazole ligation of a ferroheme is enforced without excess imidazole in solution.