Tetrahedral Co(II) coordination in α-type cobalt hydroxide:: Rietveld refinement and X-ray absorption spectroscopy

We report a Rietveld refinement analysis and X-ray absorption study on a green-color Cl--intercalated R-type cobalt hydroxide phase. The refinement clearly demonstrated that one-fifth to one-sixth of the Co(II) at octahedral sites was replaced by pairs of tetrahedrally coordinated Co(II) on each side of the hydroxide plane, represented by a structural formula of [(Co0.828Co0.348tetra)-Co-octa(OH)(2)]Cl-0.348+(0.348)center dot 0.456H(2)O. X-ray absorption spectroscopy also indicated that the divalent cobalt were in local neighboring environments of both octahedral and tetrahedral coordination. Furthermore, UV-vis spectroscopic measurements elucidate the typical green/blue color of an R-type cobalt hydroxide.