Diaqua(5-carboxybenzene-1,3-dicarboxylato-κ2 O 1,O 1′)(6,6′-dimethyl-2,2′-bipyridine-κ2 N,N′)nickel(II) heptahydrate

In the title compound, [Ni(C9H4O6)(C12H12N2)(H2O)2]·7H2O, the NiII atom is six-coordinated by two O atoms from a chelating carboxylate group of a 5-carboxybenzene-1,3-dicarboxylate ligand, two O atoms of two water molecules and two N atoms from a 6,6′-dimethyl-2,2′-bipyridine ligand in a distorted octahedral geometry. The compound exhibits a three-dimensional supramolecular structure composed of the complex molecules and lattice water molecules, which are linked together by intermolecular O—H⋯O hydrogen bonds and partly overlapping π–π interactions between the pyridine and benzene rings [centroid–centroid distances = 3.922 (2) and 3.921 (2) Å]. One of the lattice water molecules is disordered over two positions in an occupancy ratio of 0.521 (6):0.479 (6).

In the title compound, [Ni(C 9 H 4 O 6 )(C 12 H 12 N 2 )(H 2 O) 2 ]Á7H 2 O, the Ni II atom is six-coordinated by two O atoms from a chelating carboxylate group of a 5-carboxybenzene-1,3dicarboxylate ligand, two O atoms of two water molecules and two N atoms from a 6,6 0 -dimethyl-2,2 0 -bipyridine ligand in a distorted octahedral geometry. The compound exhibits a three-dimensional supramolecular structure composed of the complex molecules and lattice water molecules, which are linked together by intermolecular O-HÁ Á ÁO hydrogen bonds and partly overlappinginteractions between the pyridine and benzene rings [centroid-centroid distances = 3.922 (2) and 3.921 (2) Å ]. One of the lattice water molecules is disordered over two positions in an occupancy ratio of 0.521 (6):0.479 (6).
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Sheldrick, 2008 Comment Metallosupramolecular chemistry has received much attention due to their variety of architectures and the potential applications as functional materials (Maspoch et al., 2007;Ockwig et al., 2005). The choice of ligands and metal centers can affect the final structures. A great number of organic aromatic polycarboxylate and N-donor ligands have been successfully employed in the generation of many novel structures (Zang et al., 2006). To further explore the influence of multicarboxylate and N-donor ligands on the properties and construction of coordination compounds, we undertake synthetic and structural studies on the title compound, a Ni(II) complex based on 1,3,5-benzenetricarboxylic acid (H 3 btc) and 6,6'-dimethyl-2,2'bipyridine (dmbpy).
As shown in Fig. 1, the asymmetric unit consists of one Ni II atom, one Hbtc ligand, one dmbpy ligand, two coordinated and seven lattice water molecules. The Hbtc ligand occurs in a form with an intact COOH group. The Ni II atom is six-coordinated by two O atoms from one chelating carboxylate group of the Hbtc ligand, two O atoms of two water molecules and two N atoms from a dmbpy ligand, completing a distorted octahedral geometry. N1, N2, O1 and O2 comprise the equatorial plane, while O1W and O2W occupy the axial positions. As depicted in Fig. 2, each complex molecule is connected to four adjacent ones through hydrogen bonds (Table 1), resulting in a two-dimensional supramolecular structure in the ab plane, in which partly overlapping π-π stacking interactions involving the benzene and pyridine rings are detected [centroid-centroid distances = 3.922 (2) and 3.921 (2) Å]. Adjacent layers are associated together by hydrogen bonds with the hydroxyl groups of the intact COOH groups serving as donors and the uncoordinated carboxylate O atoms from different layers as accepters.
The lattice water molecules are fixed in the three-dimensional supramolecular net through hydrogen bonds (Fig. 3).

Experimental
The title compound was synthesized hydrothermally in a Teflon-lined stainless steel container by heating a mixture of H 3 btc (0.011 g, 0.05 mmol), dmbpy (0.009 g, 0.05 mmol), Ni(NO 3 ) 2 .6H 2 O (0.015 g, 0.05 mmol) and NaOH (0.004 g, 0.1 mmol) in 7 ml of distilled water at 120°C for 3 days, and then cooling it to room temperature. Green block crystals of the title compound were obtained in 75% yield based on nickel.

Refinement
One of the lattice water molecules is disordered over two positions in a 0.521 (6)