Bis(μ-naphthalene-1,8-dicarboxylato-κ2 O 1:O 8)bis[aquabis(N,N′-dimethylformamide-κO)copper(II)]

In the centrosymmetric dinuclear title complex, [Cu2(C12H6O4)2(C3H7NO)4(H2O)2], the coordination environment of each Cu(II) atom displays a distorted CuO5 square-pyramidal geometry, which is formed by two carboxylate O atoms of two μ-1,8-nap ligands (1,8-nap is naphthalene-1,8-dicarboxylate), two O atoms of two DMF (DMF is N,N′-dimethylformamide) and one coordinated water molecule. The Cu—O distances involving the four O atoms in the square plane are in the range 1.9501 (11)–1.9677 (11) Å, with the Cu atom lying nearly in the plane [deviation = 0.0726 (2) Å]. The axial O atom occupies the peak position with a Cu—O distance of 2.885 (12) Å, which is significantly longer than the rest of the Cu—O distances. Each 1,8-nap ligand acts as bridge, linking two CuII atoms into a dinuclear structure. Intermolecular O—H⋯O and C—H⋯O hydrogen-bonding interactions consolidate the structure.

In the centrosymmetric dinuclear title complex, [Cu 2 (C 12 H 6 O 4 ) 2 (C 3 H 7 NO) 4 (H 2 O) 2 ], the coordination environment of each Cu(II) atom displays a distorted CuO 5 squarepyramidal geometry, which is formed by two carboxylate O atoms of two -1,8-nap ligands (1,8-nap is naphthalene-1,8dicarboxylate), two O atoms of two DMF (DMF is N,N 0dimethylformamide) and one coordinated water molecule. The Cu-O distances involving the four O atoms in the square plane are in the range 1.9501 (11)-1.9677 (11) Å , with the Cu atom lying nearly in the plane [deviation = 0.0726 (2) Å ]. The axial O atom occupies the peak position with a Cu-O distance of 2.885 (12) Å , which is significantly longer than the rest of the Cu-O distances. Each 1,8-nap ligand acts as bridge, linking two Cu II atoms into a dinuclear structure. Intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bonding interactions consolidate the structure.

Comment
It is well-known that appropriate metal and ligand are the two keys for design and construction of metal-organic frameworks.
Here we choose 1,8-nap ligand (1,8-nap = naphthalene-1,8-dicarboxylate), due to its unique ability to form stable chelates in diverse coordination modes such as bidentate, meridian and bridging; which have been demonstrated in our previous work (Wen et al., 2008;Wen et al., 2007). Moreover, we select the copper to provide a set of well defined coordination geometry. A perspective view of the molecular structure of (I) is presented in Fig. 1. The coordination environment of each Cu atom displays a distorted CuO 5 square pyramidal coordination geometry, which is formed from two carboxylate oxygen atoms of two µ 2 -1,8-nap ligands, two oxygen atoms of two DMF and one coordinated water molecule; similar to some comlexes reported earlier (Abourahma et al., 2002;Bencini et al., 2003;Fokin et al., 2004;Sun et al., 2009). Four oxygen atoms O2-O3 i -O1W-O6 form a square plane (Cu-O distances in ranging 1.9501 (11) -1.9677 (11) Å), and the Cu1 atom lies in the plane (deviation 0.0726 (2) Å). The fifth oxygen atom O1 is on the peak of square pyramid, and Cu-O distance is 2.885 (12) Å, which is significantly longer than the rest of the Cu-O distances. Both carboxylate groups of the 1,8-nap ligand are deprotonated, and adopt a monodentate coordination mode. As a result, the whole 1,8-nap ligand acts as µ 2 -bridge linking two Cu II atoms to form a sixteen-atoms ring. There are intramolecular hydrogen bonds between uncoordinated O atoms of 1,8-nap ligands and water molecules, O1W···O5, O1W···O4 i (details are given in Tab. 1). In addition, weak interactions of the type C-H···O are also present. Such hydrogen-bonding interactions consolidate the dinuclear structure, as depicted in Fig. 2.
The filtrate was allowed to stand at ambient temperature. Well formed blue crystals suitable for X-ray analysis were obtained after two months (yield 45%, based on Cu).

Refinement
H atoms bonded to C atoms were positioned geometrically and included in the refinement in the riding-model approximation Crystal data [Cu 2 (C 12 (7) 0.0011 (7) Geometric parameters (Å, °)