Crystal structure of tetrakis[μ-2-(methoxycarbonyl)benzoato-κ2 O 1:O 1′]bis[(N,N-dimethylformamide-κO)copper(II)](Cu—Cu) dimethylformamide disolvate

The binuclear CuII complex displays a paddle-wheel structure. In the crystal, adjacent DMF molecules coordinated to copper atoms are arranged in a mutual ‘head-to-tail’ manner by offset face-to-face π–π stacking interactions, resulting in chains along the c-axis direction. These are assembled into a three-dimensional structure by further weak C—H⋯O and C—H⋯π interactions involving the DMF solvent molecules.

The title compound, [Cu 2 (C 9 H 7 O 4 ) 4 (C 3 H 7 NO) 2 ]Á2C 3 H 7 NO, crystallizes in the monoclinic P2 1 /c space group, with the binuclear copper unit occupying a special position on an inversion center, i.e. the asymmetric unit of the crystal consists of one Cu II ion, two 2-(methoxycarbonyl)benzoate ligands, and two DMF molecules (one coordinated and one solvate). The binuclear complex displays a paddle-wheel-shaped structure with the two copper atoms being in a Jahn-Teller-distorted octahedral coordination environment. Each 2-(methoxycarbonyl)benzoate substituent acts as a bridging ligand and links two Cu atoms with a Cu-Cu distance of 2.633 (1) Å . The carboxylate groups of the 2-(methoxycarbonyl)benzoate ligands adopt bidentate syn-syn bridging modes, with dihedral angles between the carboxylate planes and the aromatic rings of 18.427 (4) and 43.029 (6) . In the crystal, adjacent DMF molecules coordinated to copper atoms are arranged in a mutual 'head-to-tail' manner by offset face-tofacestacking interactions, resulting in chains along the c-axis direction. The planes of the coordinated DMF molecules are parallel to each other, the distance between them being 3.33 (1) Å . A three-dimensional structure is assembled from the chains by weak C-HÁ Á ÁO and C-HÁ Á Á intermolecular interactions involving the DMF solvent molecules. One of the methyl ester groups is disordered over two sites with an occupancy ratio of 0.751 (12):0.249 (12).

Structural commentary
The title compound crystallizes in the monoclinic P2 1 /c space group, with the binuclear copper unit occupying a special position on the inversion center. The asymmetric unit consists of one Cu II ion, two 2-(methoxycarbonyl)benzoate ligands, and two DMF molecules (one coordinated and one solvate). The complex displays a paddle-wheel-shaped binuclear structure (Fig. 1) (Kato et al., 1964). However, the Cu-Cu i distance in (I) is slightly longer than the Cu-Cu separation of 2.56 Å in metallic copper (Jones et al., 1997). The carboxylate groups of the 2-(methoxycarbonyl)benzoate ligands adopt bidentate syn-syn bridging modes, with the dihedral angles between the carboxylate planes and the aromatic rings of 18.427 (4) and 43.029 (6) .

Supramolecular features
The crystal structure of (I) contains both coordinated and solvate DMF molecules. As illustrated in Fig. 2, adjacent DMF molecules coordinated to copper atoms are arranged in a mutual 'head-to-tail' manner by offset face-to-facestacking interactions , resulting in chains along the c-axis direction. The planes of the coordinated DMF molecules are parallel to each other, the distance between them being 3.33 (1) Å . The three-dimensional structure of (I) is assembled from these chains by further weak C-HÁ Á ÁO interactions (HÁ Á ÁA distances of 2.63-2.70 Å ; Table 2) and intermolecular Á Á Á interactions (Fig. 3 Table 1 Selected geometric parameters (Å , ). (17) Symmetry code: (i) Àx þ 1; Ày þ 1; Àz þ 1.

Synthesis and crystallization
The title complex was synthesized according to a literature procedure (Wang et al., 2013). 2-(Methoxycarbonyl)benzoic acid (180.0 mg, 1.0 mmol) and NaOH (40.0 mg, 1.0 mmol) were dissolved in a methanol solution (20 mL) while stirring at room temperature for 20 min. Then, 15 mL of a methanol solution containing Cu(NO 3 ) 2 Á3H 2 O (121 mg, 0.5 mmol) was added to the mixture, and the mixture was further stirred at room temperature for 90 min. The blue precipitate obtained was separated by filtration, washed with methanol and dried.
The powder was dissolved in N,N-dimethylformamide, and blue single crystals were collected after slow evaporation at room temperature for several weeks.

Figure 3
The crystal packing of (I) showing the three-dimensional supramolecular network along the c axis. The intermolecular C-HÁ Á ÁO hydrogen bonds are shown as yellow dotted lines.

Tetrakis[µ-2-(methoxycarbonyl)benzoato-κ 2 O 1 :O 1′ ]bis[(N,N-dimethylformamide-κO)copper(II)](Cu-Cu) dimethylformamide disolvate
Crystal data 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.