The water soluble dicarboxylic cationic acid [(η 5 -C 5 H 4 COOH) 2 Co III ] + (1) as its Cl − salt has been treated thermally to produce the neutral zwitterion [(η 5 -C 5 H 4 COOH)(η 5 -C 5 H 4 COO)Co III ] (2). 2 reacts with HBr in water solution to yield the bromide salt of the dicarboxylic acid [(η 5 -C 5 H 4 –COOH) 2 Co III ]Br, 1Br. Preparation of the iodide [(η 5 -C 5 H 4 –COOH) 2 Co III ]I, 1I, has been achieved by direct oxidation of [(η 5 -C 5 H 4 Me) 2 Co III ]OH with KMnO 4 immediately followed by reaction with HI. The crystal structures of 1Br and 1I have been determined by single crystal X-ray diffraction. The hydrogen bonding interactions between the acid cations and between the acid cation and the halide ions have been investigated.