Crystal structure of tetrakis(μ-caproato-κ2 O:O′)bis[(4-cyanopyridine-κN 1)copper(II)]

The title dinuclear complex, [Cu2(C6H11O2)4(C6H4N2)2], has a paddle-wheel structure. The two crystallographically independent CuII atoms are each in a distorted square-pyramidal environment, in which four O atoms from the four bridging caproate ligands form the basal plane and the pyridine N atom of the 4-cyanopyridine ligand occupies the apical position. The Cu⋯Cu distance is 2.6055 (9) Å. One of the alkyl chains of the caproate ligands is disordered over two sets of sites, with occupancies of 0.725 (5) and 0.275 (5). In the crystal, two pairs of C—H⋯N hydrogen bonds connect the molecules into chains along [11-1] and C—H⋯O hydrogen bonds link the chains into a three-dimensional network.

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2012/9 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL2012/9. aryl group and L is pyridine or a pyridyl ligand, have been demonstrated as homogeneous catalysts in the oxidation of various alcohols (Abied et al., 1987;Kozlevčar et al., 1999;Bora et al., 2007;Das et al., 2007;Sarmah et al., 2010). In view of this it was found instructive to prepare other members of the above general formula having R = a long-chain alkyl group because the presence such alkyl groups could make the resultant dimeric carboxylates more soluble in organic solvents, and hence more effective as catalysts.
We aimed to prepare complexes of long chain carboxylic acids as only a few crystal structures of such complexes of copper(II) have been reported (Petrič et al., 1995;Lomer & Perera, 1974 (Catterick & Thornton, 1977). In (I), one pair of hydrocarbon chains has the common zigzag conformation while the other pair is distorted, which facilitates efficient packing.

S2. Experimental
CuSO 4 ·5H 2 O (0.749 g, 3 mmol) was dissolved in methanol (25 ml). To this solution, sodium caproate (C 5 H 11 COONa; 0.882 g, 6 mmol) and 4-cyanopyridine (0.321 g, 3 mmol) were added and the mixture was stirred for 2 h. The resulting green product was filtered off, washed with small volumes of methanol and dried in a vacuum desiccator over fused CaCl 2 (yield 80%). The product was dissolved in acetonitrile to get a greenish homogeneous solution which was allowed to concentrate by evaporation at room temperature. Single crystals suitable for X-ray diffraction were obtained from this solution after one day and collected by filtration.

S3. Refinement
H atoms were located in a difference Fourier map and were subsequently treated as riding with C-H = 0.95-0.99 Å, and with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). One of the alkyl chains of caproato ligands is disordered over two sites with refined occupancies of 0.725 (5) and 0.275 (5). Restraints of same displacement parameters (SIMU) and same distances (SADI) were applied for the disordered C atoms, C32-C36 and C32′-C36′.
supporting information sup-2 . E71, m195-m196  A packing diagram of the title compound. Hydrogen bonds are shown by dotted lines.

Tetrakis(µ-caproato-κ 2 O:O′)bis[(4-cyanopyridine-κN 1 )copper(II)]
Crystal data Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. One of the four pentane side chains was found to be two fold disordered·The components of disorder could be completed through successive difference fourier·The two components were refined with sum of their occupancies restrained as 1. Also the bond distances and thermal parameters of the disordered components were restrained to be with in chemically meaningful range. Finally when the refinement converged the relative occupancies were 0.725 and 0.275. The alkyl and aromatic H atoms were allowed to ride at a distance of 0.99 Å and 0.95 Å respectively during refinement.