Extended structure of indium(III) protoporphyrin IX acetate mimics dimer structure of hematin anhydride

Abstract

A complex of indium(III) protoporphyrin IX acetate was prepared and characterized crystallographically as its pyridine solvate. The structure of the 5-coordinate In complex is dimeric through a strong bridging hydrogen bond between the propionic acid group of one porphyrin unit and the carbonyl of the In-bound acetate, leading to a structure that mimics the reciprocal dimer structure of the malaria pigment hemozoin with an expanded frame. Inter-dimer π-stacking and hydrogen bonding interactions of the propionic acid groups are the dominant structural features. This result, following the report of reciprocal dimers of gallium(III) protoporphyrin IX species, indicates that this is a common motif for metalloprotoporphyrin IX species.