Dicobalt copper bis[orthophosphate(V)] monohydrate, Co2.39Cu0.61(PO4)2·H2O

In an attempt to hydrothermally synthesize a phase with composition Co2Cu(PO4)2·H2O, we obtained the title compound, Co2.39Cu0.61(PO4)2·H2O instead. Chemical analysis confirmed the presence of copper in the crystal. The crystal structure of the title compound can be described as a three- dimensional network constructed from the stacking of two types of layers extending parallel to (010). These layers are made up from more or less deformed polyhedra: CoO6 octahedra, (Cu/Co)O5 square pyramids and PO4 tetrahedra. The first layer is formed by pairs of edge-sharing (Cu/Co)O5 square pyramids linked via a common edge of each end of the (Cu/Co)2O8 dimer to PO4 tetrahedra. The second layer is undulating and is built up from edge-sharing CoO6 octahedra. The linkage between the two layers is accomplished by PO4 tetrahedra. The presence of water molecules in the CoO4(H2O)2 octahedron also contributes to the cohesion of the layers through O—H⋯O hydrogen bonding.

The network is built up from three different types of polyhedra more or less distorted: CoO 6 octahedra , (Cu/Co)O 5 square-pyramids and PO 4 tetrahedra. One octahedron (Co1), slightly distorted, has a coordination sphere composed of O atoms from PO 4 groups, while that of the other (Co2) is made up of four O atoms from PO 4 groups and by two water molecules (O9). This fact explains its more pronounced distortion, with Co-O bond lengths in the range 2.0407 (11)-2.3310 (13) Å.
All CoO 6 octahedra are linked together by edge-sharing and sharing three corners of PO 4 tetrahedra, in the way to built a layer parallel to (010) as shown in Fig. 2. Therefore, the presence of the water molecule involved in the formation of the CoO 4 (H 2 O) 2 octahedron causes a corrugation in this layer through O-H···O hydrogen bonds. Furthermore, Fig. 3 shows that each pair of distorted square-pyramids share an edge and built up a dimer linked to two regular PO 4 tetrahedra via a common edge. The sequence of (Cu/Co)O 5 and PO 4 polyhedra leads to the formation of another layer (Fig. 3). As a matter of fact, the network of this structure can be described by stacking these two types of layers as represented in Fig. 4 (Harrison et al., 1995).

Refinement
All H atoms were initially located in a difference map and refined with a O-H distance restraint of 0.84 (1) Å. Later they were refined in the riding model approximation with U iso (H) set to 1.5 U eq (O). Refinements of the site ocupancy factors of the metal sites revealed the octahedrally coordinated sites solely occupied by Co, whereas the 5-coordinated site shows a mixed occupancy of Co:Cu = 0.387 (11):0.613 (11). Fig. 1

Special details
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.