Tetrakis[μ-2-(methoxycarbonyl)benzoato-κ2 O 1:O 1′]bis[(acetonitrile-κN)copper(II)](Cu—Cu)

In the binuclear copper(II) title complex, [Cu2(C9H7O4)4(C2H3N)2], an inversion centre is situtated at the mid-point of the Cu—Cu bond. The CuII atom together with its four coordinated O atoms are in a distorted planar square arrangement while the nitrogen and the other CuII atom are located in apical positions. The whole molecule looks like a paddle-wheel. In the crystal, chains are assembled along the b axis through C—H⋯O hydrogen bonds and slipped π–π interactions between the benzene rings of neighbouring molecules [centroid–centroid distance = 3.6929 (3) Å and slippage = 0.641 (1) Å].


Related literature
For a review on related binuclear Cu II carboxylato compounds with subnormal magnetic moments, see: Kato et al. (1964). For the electrochemical behavior of related compounds, see: Reinhard et al. (2003). For the synthesis of related compounds, see: Liu et al. (2008).
Herein we report synthesis and crystal structure of binuclear copper(II) carboxylato compound with 2-(methoxycarbonyl)benzoic acid acting as a bidentate chelating ligand. Each copper(II) is coordinated by four carboxylate O donor atoms from four ligands, and by N donor atoms from the solvent molecule, The Cu-O distances and related angles are all within expected ranges (Kato et al., 1964) and Cu-N distance is 2.186 (3) Å. A binuclear copper carboxylate unit is formed by four (HL) ligands and two Cu centres with a Cu-Cu separation of 2.6662 (7) Å.

Experimental
The title complex was prepared by adapting a reported procedure (Liu et al., 2008) by stirring a methanolic solutions of 2-(methoxycarbonyl)benzoic acid (180.0 mg, 1.0 mmol) and NaOH (40.0 mg, 1.0 mmol) for 30 min at room temperature.
Then, 10 ml of a methanol solution containing Cu(NO 3 ) 2 .3H 2 O (121 mg, 0.5 mmol) was added to the mixture, the blue precipitate obtained was separated by filtration, washed with methanol and dried. The blue powder was dissolved in acetonitrile, and single crystals of the title complex suitable for X-ray analysis were obtained after slow evaporation at room temperature for several weeks.

Refinement
H atoms attached to C atoms are placed in geometrically idealized position, with C-H=0.93 and 0.96 Å, for CH and CH 3 groups, respectively, and with U iso (H)=1.2U eq (C sp2 ) or 1.5U eq (C sp3 ).  Molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level. The H atoms attached to C atoms were omitted for clarity. Atoms with the A label are generated by the (1 -x, 1 -y, 1 -z) symmetry operation.

Figure 2
View of the crystal packing along the a axis. Hydrogen-bonding and π-π interactions are represented by black dashed lines and pink dashed lines, respectively (all distances in Å). For the sake of clarity, H atoms not involved in hydrogen bonding have been omitted.

Tetrakis[µ-2-(methoxycarbonyl)benzoato-κ 2 O 1 :O 1′ ]bis[(acetonitrile-κN)copper(II)](Cu-Cu)
Crystal data [Cu 2 (C 9 H 7 O 4 ) 4 (C 2 H 3 N) 2 ] M r = 925.77 Triclinic, P1 Hall symbol: -P 1 a = 8.2332 (10)   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 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.