Bis{tris[3-(2-pyridyl)-1H-pyrazole]nickel(II)} dodecamolybdo(V,VI)phosphate hexahydrate

The hydrothermally prepared title compound, [Ni(C8H7N3)3]2[PMo12O40]·6H2O, is a member of the isotypic series [(M(C8H7N3)3]2[PMo12O40]·6H2O where M is Mn, Cd, and Fe. The Ni2+ cation is in a distorted octahedral environment, coordinated by six N atoms from three chelating 3-(2-pyridyl)-1H-pyrazole ligands. In the one-electron reduced heteropolyanion, two O atoms of the central PO4 group ( symmetry) are equally disordered about an inversion centre. N—H⋯O and O—H⋯O hydrogen bonds contribute to the crystal packing. Compared with the isotypic structures, the main difference is related with the M—N bond lengths, whereas all other bond lengths, angles and the hydrogen-bonding motifs are very similar.

As shown in Figure 1, the asymmetric unit of the title compound consists of three subunits, viz. of a complex [Ni(C 8 (2000); Kurmoo et al. (1998);Niu et al. (1999). The employed organic ligand appears to adjust the pH value, and additionally supplies reducing electrons, which is a commonly observed feature of hydrothermal syntheses when organic amines are used to prepare various hybrid materials, zeolites or metal phosphates (Yang et al., 2003).
In the Keggin-type heteropolyanion, each Mo atom is surrounded by six O atoms and the P atom is located at the center  Table 2).
TGA curve shows a separation of lattice water molecules and the organic ligands above 343 and 682 K, respectively.
The overall thermal decomposition process can be described by the followed equation

Refinement
All hydrogen atoms bound to aromatic carbon atoms were refined in calculated positions using a riding model with a C-H distance of 0.93 Å and U iso = 1.2U eq (C). Hydrogen atoms attached to aromatic N atoms were refined with a N-H distance of 0.86 Å and U iso = 1.2U eq (N). The hydrogen atoms of the three uncoordinated water molecules could not be located unambiguously from difference Fourier maps, probably due to disorder of the water molecules. Thus the structure was refined without the H atoms of the water molecules (which includes the water O atoms O1W, O2W, O3W). In the PO 4 unit, the two oxygen atoms (O19 and O21) are equally disordered about the inversion centre. In the final difference Fourier map the highest peak is 2.70 Å from atom O2w and the deepest hole is 1.25 Å from atom O12. The highest peak is located in the voids of the crystal structure and may be associated with an additional water molecule. However, refinement of this position did not result in a reasonable model. Hence this position was also excluded from the final refinement.
Figures Fig. 1. The building blocks of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level; H atoms are given as spheres of arbitrary radius.

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.