Bis{4,4′-[oxalylbis(azanediyl)]dipyridinium} octamolybdate

In the crystal structure of the title compound, (C12H12N4O2)2[Mo8O26], the amino and pyridinium groups of the N 1,N 2-di(pyridinium-4-yl)oxalamide cations are hydrogen bonded to the O atoms of the centrosymmetric isopolyoxometalate β-[Mo8O26]4− anions, forming a three-dimensional supramolecular architecture.

In the crystal structure of the title compound, (C 12
Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL. The nanoscopic sizes (Cronin, et al., 2002;Fukaya & Yamase, 2003,) and thier diversified shapes of discrete POMs have attracted great interest. The design, synthesis and structural characterization of inorganic-organic hybrid compounds base on POMs, for which many properties and applications can be predicted, have established a new field of research in the chemistry of biology and materials sciences (Luan, et al., 2002;Cui, et al., 2003;Wang, et al., 2003). Different N-heterocycle ligands can lead to different inorganic-organic hybrid compounds based on POMs. N 1 ,N 2 -di(pyridin-4-yl)oxalamide (L), is a bis-pyridine ligand, which has been reported only rarely in the construction of hybrid compounds based on POMs. In the present work, the title complex was synthesized hydrothermally by reacting L with the isopolyoxometalate, Mo 8 O 26 .
The molecular structure of the title complex is illustrated in Fig. 1. In the asymmetric unit there is a doublely protonated L molecule, and half an isopolyoxometalate unit. The bond distances and angles in the cation are similar to those observed previously for N 1 ,N 2 -di(pyridin-4-yl)oxalamide (Tzeng, et al., 2007). For the anion, [Mo 8 O 26 ] 4-, the geometrical parameters are similar to those reported by (Gong, et al., 2007).
In the crystal the protonated pyrdidinium groups and the amino group form N-H···O hydrogen bonds with the oxygen atoms of the centrosymmetric [Mo 8 O 26 ] 4anions, leading to the formation of a three dimensional supramolecular network (Table 1 and Fig. 2).
The synthesis was carried out hydrothermally using a Teflon-lined autoclave. The reaction mixture was heated at 393 K for 3 days, followed by slow cooling to rt. The resulting colorless prismatic crystals were filtered off and washed with water   Table 1 for details.

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 > 2sigma(F 2 ) is used only for calculating R-factors(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