Diaquabis(2,2′-biimidazole)zinc(II) 4,4′-dicarboxybiphenyl-3,3′-dicarboxylate

In the title compound, [Zn(C6H6N4)2(H2O)2](C16H8O8), the ZnII atom, located on an inversion centre, is coordinated by two aqua and two bidentate biimidizole ligands, resulting in a slightly distorted octahedral ZnO2N4 geometry. The four N atoms from the two biimidizole ligands lie in the equatorial plane and the two aqua O atoms lie in the axial sites. The biphenyltetracarboxylate anion also lies on an inversion centre. The ZnII complex cation and the anion are held together by N—H⋯O hydrogen bonds, forming a zigzag chain along [21]. The chains are further connected by water molecules via O—H⋯O hydrogen bonds.

In the title compound, [Zn(C 6 H 6 N 4 ) 2 (H 2 O) 2 ](C 16 H 8 O 8 ), the Zn II atom, located on an inversion centre, is coordinated by two aqua and two bidentate biimidizole ligands, resulting in a slightly distorted octahedral ZnO 2 N 4 geometry. The four N atoms from the two biimidizole ligands lie in the equatorial plane and the two aqua O atoms lie in the axial sites. The biphenyltetracarboxylate anion also lies on an inversion centre. The Zn II complex cation and the anion are held together by N-HÁ Á ÁO hydrogen bonds, forming a zigzag chain along [211]. The chains are further connected by water molecules via O-HÁ Á ÁO hydrogen bonds.
only for their intriguing structural motifs but also for their potential applications in the areas of catalysis, separation, gas absorption, molecular recognition, nonlinear optics and magnetochemistry (Hagrman et al., 1999;Jia et al., 2007;Kortz et al., 2003). In this paper, we report the structure of the title compound, (I).
As shown in Fig. 1, the Zn II atom (site symmetry 1) is bonded to two aqua and two bidentate biimidizole ligands, to result in a slightly distorted octahedral ZnO 2 N 4 geometry for the central metal. The Zn II atom lies on an inversion centre, as a consequence which the asymmetric unit comprises a half of the molecule. The four nitrogen atoms belonging to two biimidizole ligands lie in the equatorial plane and the two aqua oxygen atoms lie in the axial coordination sites. The bonds around Zn is listed in Table 1. The 3,3',4,4'-biphenyl tetracarboxylate acts as negative electron balance. With two kinds of hydrogen bonds of N4-H4A···O2 and N1-H1A···O1, a zigzag chain is formed. Furthermore, a 3-D frameworks is constructed with O1W-H2W···O2 and O1W-H1W···O4 along the c axis, shown in Fig. 2.

Refinement
Atom H3A on O3 was located in a difference Fourier map and refined with an O-H distance [0.93 (1) Å] restraint. O-bound H atoms except H3A and N-bound H atoms were located in a difference Fourier map and were constrained as riding, with U iso (H) = 1.2U eq (O or N). Other H atoms were placed in calculated positions (C-H = 0.93 Å) and refined as riding, with Fig. 1. The molecular components of the title compound, drawn with 30% probability displacement ellipsoids for the non-hydrogen atoms.

Special details
Geometry. All e.s. 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.  (3) 165 (4) Symmetry codes: (iii) −x+2, −y, −z+1; (iv) −x+1, −y+1, −z+1; (ii) −x+1, −y, −z+1.