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)]Br-2(BF4) 1 and [Co(NH3)(6)]Cl-2(HC2O4)center dot H2O 2 have been prepared and structurally characterised. The two crystallographically independent cations in I are involved in different hydrogen bonding patterns, with one forming predominantly N-H center dot center dot center dot F interactions with the tetrafluoroborates and the other forming N-H center dot center dot center dot Br hydrogen bonds. The supramolecular structure of 2 shows unusual hydrogen oxalate-water chains in addition to N-H center dot center dot center dot O and N-H center dot center dot center dot 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. (c) 2006 Elsevier B.V. All rights reserved.