A second polymorph with composition Co3(PO4)2·H2O

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.

Single crystals of Co 3 (PO 4 ) 2 ÁH 2 O, 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, Zn 3 (PO 4 ) 2 ÁH 2 O. Three independent Co 2+ 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-HÁ Á ÁO stabilize this arrangement.
We gratefully acknowledge the Brain Korea 21 programme and the Australian Research Council for support. and high pressure, have been investigated for many years (Murugavel et al., 2008). This is not only because of the multifarious structural chemistry, but also due to many potential applications. For a listing of reviews on these materials, see Lee et al. (2008). We are currently investigating the synthesis of a variety of similar functional materials through templation effects under hydrothermal conditions. The title compound, Co 3 (PO 4 ) 2 .H 2 O, (I), and the related compound Co 3 (PO 4 ) 2 .4H 2 O (Lee et al., 2008) were synthesized as a part of these studies.
In the past, many different cobalt(II) orthophosphates have been described, ranging from the anhydrous form Co 3 (PO 4 ) 2 to its corresponding octahydrate (Mellor, 1935 (Anderson et al., 1976) versus 704.1 Å 3 (this study)) and exhibits also a different assembly of the structural building units. The second polymorph (I) is isotypic with its Zn analogue Zn 3 (PO 4 ) 2 .H 2 O (Riou et al., 1986).
The structure of (I) contains three different Co 2+ centres bridged by orthophosphate anions (Fig 1) is bonded to five O atoms of four phosphate ligands (one bidentate) and the sixth coordination site is occupied by a water molecule. This assembly leads to the formation of a three-dimensional framework (Fig. 2), which is stabilized by additional O-H···O hydrogen bonds (Table 2).

Experimental
Conditions of the hydrothermal single crystal growth of the hydrous cobalt(II) orthophosphates Co 3 (PO 4 ) 2 .H 2 O and Co 3 (PO 4 ) 2 .4 H 2 O were described in detail in a preceding communication (Lee et al., 2008).

Refinement
Water H atoms were located in difference Fourier maps and were refined with U iso (H) values fixed at 1.5U eq of the parent O atoms. O-H bond length restraints of 0.89 (1) Å were also employed. The highest peak and the deepest hole in the final Fourier map are located 1.74 Å from O1 and 0.20 Å from P1, respectively.
supplementary materials sup-2 Figures   Fig. 1. The asymmetric unit of compound (I), drawn with displacement parameters at the 50% probability level. H atoms are given as spheres of arbitrary radius.

Special details
Experimental. The crystal was coated in Exxon Paratone N hydrocarbon oil and mounted on a thin mohair fibre attached to a copper pin. Upon mounting on the diffractometer, the crystal was quenched to 150(K) under a cold nitrogen gas stream supplied by an Oxford Cryosystems Cryostream.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq