The structure of [Co(H2O)6](BrO4)2 consists of stacks of water-oxygen
octahedra, alternate ones of which contain a central Co(II) ion, each
surrounded by six stacks of perbromate ions. The water O atoms form a
virtually regular octahedron about Co, while the perbromate geometry i
s nearly regular tetrahedral. The structure is compared with those of
[Hg(H2O)6]-(ClO4)2, [Cd(H2O)6](ClO4)2 and [Ni(H2O)6](BrO4)2. Although
the structures of the perchlorates cited above are broadly similar to
that of the title salt, and although all three structures have been as
signed in space group P3m1BAR, the perchlorates and the title salt are
not isostructural. Location and isotropic refinement of the single ty
pe of H atom permitted detailed analysis of the hydrogen bonding. From
the point of view of the water molecules, the hydrogen bonding is rem
arkably similar, even in quantitative detail, to that of the water mol
ecules in [Co(H2O)6]-(BrO3)2.