Bis{tris[3-(2-pyridyl)-1H-pyrazole]nickel(II)} dodecamolybdosilicate tetrahydrate

The asymmetric unit of the title compound, [Ni(C8H7N3)3]2[SiMo12O40]·4H2O, consists of a complex [Ni(C8H7N3)3]2+ cation, half of a Keggin-type heteropolyanion [SiMo12O40]4− and two uncoordinated water molecules. The Ni2+ cation is surrounded in a slightly distorted octahedral coordination by six N atoms from three chelating 3-(2-pyridyl)-1H-pyrazole ligands. In the heteropolyanion, two O atoms of the central SiO4 group ( symmetry) are equally disordered about an inversion centre. N—H⋯O and O—H⋯O hydrogen bonding between the cations, anions and the uncoordinated water molecules leads to a consolidation of the structure.

The asymmetric unit of the title compound, [Ni(C 8 4À and two uncoordinated water molecules. The Ni 2+ cation is surrounded in a slightly distorted octahedral coordination by six N atoms from three chelating 3-(2-pyridyl)-1H-pyrazole ligands. In the heteropolyanion, two O atoms of the central SiO 4 group (1 symmetry) are equally disordered about an inversion centre. N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonding between the cations, anions and the uncoordinated water molecules leads to a consolidation of the structure.
Financial support from the Chinese Academy of Sciences ('Hundred Talents Program')  as well as their potential medical applications (Pope & Müller, 1991). In our research group, organic amines, such as 3-(2pyridyl)pyrazole and pyrazine, are used to effectively modify polyoxomolybdates under hydrothermal condictions Zhang, Wei, Sun et al., 2009;Zhang, Wei, Shi et al., 2010). Here, we describe the synthesis and structural characterization of the title compound.
The TGA curve shows that the lattice water molecules and the organic ligands separate above ca 326 and 657 K, respectively. The overall thermal decomposition process can be described by the followed equation: C 48 H 50 Mo 12 N 18 Ni 2 O 44 Si + 81O 2 → 25H 2 O + 48CO 2 + 9N 2 O 5 + 2NiO + SiO 2 + 12MoO 3 .

Experimental
A mixture of 3-(2-pyridyl)pyrazole (1 mmoL 0.14 g), sodium molybdate (2 mmoL, 0.48 g), sodium silicate nonahydrate (0.2 mmoL, 0.05 g) and nickel(II) chloride hexahydrate (0.25 mmol, 0.05 g) in 10 ml distilled water was sealed in a 25 ml  3376, 3136, 2961, 1614, 1568, 1522, 1457, 1439, 1364, 1300, 1097, 950, 913, 812, 636, 507. supplementary materials sup-2 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 two 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 O21, O22). In the SiO 4 unit, the two oxygen atoms (O1 and O18) are equally disordered about the inversion centre. One of the bridging O atoms (O12) is also disordered and was refined with split positions and an occupancy ratio of 1:1. In the final difference Fourier map the highest peak is 2.87 Å from atom O22 and the deepest hole is 0.11 Å from atom O8. 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.

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.