Crystal structure of Ba2Co(BO3)2.

Single crystals of dibarium cobalt(II) bis-(orthoborate), Ba2Co(BO3)2, have been obtained from the melt. The crystal structure is composed of two isolated (BO3)3- triangles linked to Co2+ cations. The resulting [CoO5] square pyramids and the borate anions make up branched rows extending parallel to [010]. The barium cations occupy two sites in the voids of this arrangement and exhibit coordination numbers of nine each. A comparison with the structures of other A 2 M(BO3)2 compounds reveals a unique five-coordination of the small metal M in the title compound instead of four- or six-coordination for the other A 2 M(BO3)2 compounds with M = Cu, Zn, Mg, Ca, or Cd.