Crystal structure of catena-poly[[chlorido(4,4′-dimethyl-2,2′-bipyridine-κ2 N,N′)copper(II)]-μ-chlorido]

The structure of a previously unknown form of dichlorido(4,4′-dimethyl-2,2′-bipyridine)copper(II) was obtained via a DMSO-mediated dehydration of Cu(4,4′-dimethyl-2,2′-bipyridine)copper(II)·0.25H2O. The crystal structure reveals chloride-bridged copper(II) chains connected via intermolecular C—H⋯Cl hydrogen bonds.


Chemical context
Bipyridine complexes of copper(II), [(2,2 0 -bipy)CuX 2 ] (X = Cl, Br) have been used in a number of important applications in recent years, most notably in the areas of catalysis for organic synthesis (Ricardo et al., 2008;Csonka et al., 2008;Thorpe et al., 2012), DNA cleavage (Jaividhya et al., 2012), degradation of pesticides (Knight et al., 2014) and water oxidation (Barnett et al., 2012). Such complexes are characterized by an extensive number of metal coordination geometries including square-planar/tetrahedral, square-pyramidal/trigonal-bipyramidal and distorted octahedral. The associated halide ligands (chloride, bromide) can adopt terminal or bridging bonding modes leading to monomeric, dimeric or polymeric chain structures which can influence complex solubility in organic solvents and consequently their possible application in homogeneous catalysis. A third factor which influences the structural forms of these complexes is the nature of the solvent, with strongly coordinating ligands forming solvent adducts. For example, the reaction of dimethyl-2,2 0 -bipyridine with Cu I and/or Cu II in DMSO or water led to the isolation of 10 different crystalline materials, suggesting that a large number of structural motifs are possible including five-coordinate monomers, distorted tetrahedral monomers, stacked planar monomers, stacked planar bibridged dimers and and five-coordinate bibridged dimers (Willett et al., 2001). A large number of ring-substituted 2,2 0bipyridine complexes have also been prepared and characterized including dichlorido(4,4 0 -dimethyl-2,2 0 -bipyridine) copper(II) hemihydate. In this paper we describe the synthesis and structural characterization of a previously unknown form of dichlorido(4,4 0 -dimethyl-2,2 0 -bipyridine)copper(II) via a DMSO-mediated dehydration of Cu(4,4 0 -dimethyl-2,2 0 -bipyridine)Cl 2 Á0.25H 2 O. The crystal structure reveals single chlorido-bridged copper(II) chains with a distorted trigonalbipyramidal geometry of the metal cations. We conclude that the presence of the 4,4 0 -dimethyl substituents does not prevent the formation of a catenated structure, which was previously suggested as an explanation for the dimeric arrangement in Cu(4,4 0 -dimethyl-2,2 0 -bipyridine)Cl 2 Á0.5H 2 O (Gonzá lez et al., 1993).

Structural commentary
In the title complex (1), Fig. 1, the central Cu II atom is coordinated by the two nitrogen atoms, N1 and N12 of the chelating 2,2 0 -bipyridine subunit and three chlorine atoms, one terminal (Cl1) with a short Cu-Cl bond, and two bridging chlorine atoms (Cl2), which are symmetry equivalent. The bridging chlorine ligand links Cu atoms into chains via one medium and one long Cu-Cl bond [2.3320 (10) and 2.5623 (9) Å ]. The geometry around the Cu ion is best described as a distorted trigonal bipyramid with the coordination polyhedron defined by the two N atoms and three Cl atoms, one of which links the monomeric subunits into a chain, which contrasts with the four-coordinate square-planar geometry found in Cu(2,2 0 -bipyridine)Cl 2 (Wang et al., 2004;Garland et al., 1988 Symmetry codes: (i) x À 1; Ày þ 2; z À 1 2 ; (ii) x À 1 2 ; Ày þ 3 2 ; z À 1 2 .

Figure 1
ORTEP-style view of compound (1), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
Selected portion of the crystal packing diagram of compound (1), showing interchain C-HÁ Á ÁCl hydrogen bonding (see Table 1 for details).
atom. The terminal Cu1-Cl1 and medium-length bridging Cu1-Cl2 bond lengths in (1) (12) to Cu, similar to that found in the above-mentioned structures, 80.5 (3), 79.6 (3) and 80.2 (1) respectively, and forming a virtually planar five-membered ring. The C-C and C-N bond lengths and angles are within expected limits.

catena-Poly[[chlorido(4,4′-dimethyl-2,2′-bipyridine-κ 2 N,N′)copper(II)]-µ-chlorido]
Crystal data Absolute structure: Classical Flack method preferred over Parsons because s.u. lower (Flack, 1983). Absolute structure parameter: 0.011 (15) 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.