Poly[bis{3,3′-[(biphenyl-4,4′-diyl)dimethylene]diimidazol-1-ium} γ-octamolybdate(VI)]

In the title compound, {(C20H20N4)2[Mo8O26]}n, the asymmetric unit contains half of an [Mo8O26]4− anion and one 3,3′-[(biphenyl-4,4′-diyl)dimethylene]diimidazol-1-ium dication. In the anion, four distorted [MoO6] octahedra are connected via edge-sharing, forming an [Mo4O13]2− building block, composed of Mo—O(t), Mo—O(μ2), Mo—O(μ3) and Mo—O(μ4) units, with Mo—O distances ranging from 1.6858 (15) to 2.4785 (13) Å. The γ-type [Mo8O26]4− anion is completed by crystallographic inversion symmetry and is linked into an infinite chain along [100] by corner-sharing. The anionic chains and the cations are joined by N—H⋯O hydrogen bonds, generating layers extending parallel to (001).

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2312). Poly[bis{3,

metal-organic compounds
H. Liu, L. Su, L. Wang and W. Li

Comment
Polyoxometalates of molybdenum are an interesting class of metal-oxido compounds. Recently, many organic-inorganic hybrids have been reported (Zaworotko, 1998;Hong & Do, 1998) because they possess unique architectures and their cooperative functional properties have attracted considerable attention (Carlucci et al., 2003;Moulton & Zaworotko, 2001).
In this paper, we present the hydrothermal synthesis and crystal structure of the title compound, (C 20 (Modec et al., 2003). The γ-octamolybdate units are finally linked together through sharing common vertices to form infinite chains extending along [100] (Fig. 2). These chains are linked through N-H···O hydrogen bonding to generate layers extending parallel to (001) (Fig. 3).

Experimental
A mixture of (NH 4 ) 6 Mo 7 O 24 . 4H 2 O (0.12 g, 0.1 mmol), L (0.031 g, 0.2 mmol) (Fei et al., 2000) and H 2 O (10 ml) was adjusted with HCl (6M) to pH = 4-5. Then the mixture was placed in a 23 ml Teflon-lined stainless steel container. The container was heated to 423 K and held at that temperature for 72 h, and cooled to room temperature. Colorless crystals were collected in 67% yield.

Refinement
All H atoms on C atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 Å for aromatic C atoms and C-H = 0.97 Å for aliphatic C atoms, and U iso (H) = 1.2U eq and 1.5U eq (C), respectively. H atoms of the protonated N atoms in the cation were located in a difference Fourier map and were refined freely.
supplementary materials sup-2 Figures Fig. 1. A displacement ellipsoids view of the building units of (I), drawn at the 30% probability level.
Crystal data (C 20

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 )