Key indicators: single-crystal X-ray study; T = 150 K; mean (Co-O) = 0.003 Å; R factor = 0.035; wR factor = 0.103; data-to-parameter ratio = 12.2.Single crystals of Co 3 (PO 4 ) 2 Á4H 2 O, tricobalt(II) bis[orthophosphate(V)] tetrahydrate, were obtained under hydrothermal conditions. The title compound is isotypic with its zinc analogue Zn 3 (PO 4 ) 2 Á4H 2 O (mineral name hopeite) and contains two independent Co 2+ cations. One Co 2+ cation exhibits a slightly distorted tetrahedral coordination, while the second, located on a mirror plane, has a distorted octahedral coordination environment. The tetrahedrally coordinated Co 2+ is bonded to four O atoms of four PO 4 3À anions, whereas the six-coordinate Co 2+ is cis-bonded to two phosphate groups and to four O atoms of four water molecules (two of which are located on mirror planes), forming a framework structure. In addition, hydrogen bonds of the type O-HÁ Á ÁO are present throughout the crystal structure. Related literatureBesides crystals of the title compound, crystals of (2000). The structure of the isotypic mineral hopeite was first described by Liebau (1965). ExperimentalCrystal data

Single crystals of Co3(PO4)2·H2O, tricobalt(II) bis­[ortho­phosphate(V)] monohydrate, were obtained under hydro­thermal conditions. The compound is the second polymorph of this composition and is isotypic with its zinc analogue, Zn3(PO4)2·H2O. Three independent Co2+ cations are bridged by two independent orthophosphate anions. Two of the metal cations exhibit a distorted tetra­hedral coordination while the third exhibits a considerably distorted [5 + 1] octa­hedral coordination environment with one very long Co—O distance of 2.416 (3) Å. The former cations are bonded to four different phosphate anions, and the latter cation is bonded to four anions (one of which is bidentate) and one water mol­ecule, leading to a framework structure. Additional hydrogen bonds of the type O—H⋯O stabilize this arrangement.