Hexaamminecobalt(III) complexes as multiple hydrogen bond donors: Synthesis, characterization and X-ray structural study of mixed anion complexes [Co(NH3)6]Br2(BF4) and [Co(NH3)6]Cl2(HC2O4)·H2O

The compounds [Co(NH3)6]Br2(BF4) 1 and [Co(NH3)6]Cl2(HC2O4)·H2O 2 have been prepared and structurally characterised. The two crystallographically independent cations in 1 are involved in different hydrogen bonding patterns, with one forming predominantly NH⋯F interactions with the tetrafluoroborates and the other forming NH⋯Br hydrogen bonds. The supramolecular structure of 2 shows unusual hydrogen oxalate–water chains in addition to NH⋯O and NH⋯Cl interactions. An analysis of crystal structures containing [Co(NH3)6]3+ and mixed anions reveals that multiple hydrogen bonds between cations and anions can lead to both face- and edge-capping of the [Co(NH3)6]3+ octahedron.