Crystal structure of μ-oxalodihydroxamato-bis[(2,2′-bipyridyl)(dimethyl sulfoxide-κO)copper(II)] bis(perchlorate)

In this article we report a synthetic procedure and structure of the novel dinuclear copper(II) complex, with a bridging oxalodihydroxamate ligand and terminal 2,2′-bipyridine and DMSO ligands completing the square pyramidal coordination spheres of the Cu(II) centres..


Structural commentary
The title compound (I) consists of a centrosymmetric complex di-cation [Cu 2 (C 10 H 8 N 2 ) 2 (-C 2 H 2 N 2 O 4 )(C 2 H 6 SO) 2 ] 2+ with two uncoordinating perchlorate counter-anions (Fig. 1). The two copper(II) cations are connected through a doubly deprotonated oxalodihydroxamic acid, which serves as a bridging ligand between the copper ions which are coordinated by two nitrogen atoms from the 2,2 0 -bipyridine ligand, one carbonyl oxygen atom and the deprotonated hydroxamate nitrogen atom from one half of the oxalodihydroxamato ligand and the O atom of a DMSO molecule. The oxalodihydroxamato dianion is in a trans-form, while for metallacrown formation the cis-form is preferred. The coordination sphere of the copper(II) cation is square-pyramidal ( = 0.21; Addison et al., 1984) and the copper(II) ion deviates from the mean plane of the O1/N1/N2/N3 donor atoms by 0.1868 (2) Å . The separation between the copper (II) cations is 5.2949 (4) Å . The equatorial Cu-N and Cu-O distances are typical of those for copper(II) complexes with hydroxamate and oxime donor groups (Buvailo et al., 2012;Duda et al., 1997;Pavlishchuk et al., 2011b;Safyanova et al., 2015, Table 1, is most likely due to Jahn-Teller distortion. The C-N and C-C bond lengths in the 2,2 0 -bipyridine ligands are also normal for 2-substituted pyridine derivatives (Krä mer et al., 2000;Strotmeyer et al., 2003;Fritsky et al., 2004). The coordinating oxalohydroxamate dianion also has C-C, C-N, N-N bond lengths that are typical of Ndeprotonated hydroxamate groups (Ś wią tek-Kozłowska et al., 2000;Dobosz et al., 1999).

Supramolecular features
In the crystal structure, O5-H5OÁ Á ÁO6 together with C12-H12AÁ Á ÁO9 hydrogen bonds link the cations and associated perchlorate anions. An extensive series of other C-HÁ Á ÁO contacts, Table 2, link the complex cations to other anions. The O2 atom of the DMSO ligand acts as a bifurcated acceptor forming C4-H4Á Á ÁO2 and C7-H7Á Á ÁO2 hydrogen bonds. These hydrogen bonds combine withcontacts between the N2/C6-C10 ring of the bipyridine and the Cu1/O1/C11/ C11 i /N3 ring formed by the chelating oxalodihydroxamate ligand with a centroid-to-centroid distance of 3.6371 (12) Å to stack the cations along the a-axis direction, The crystal structure of complex (I), showing the atom labeling. Displacement ellipsoids are drawn at the 50% probability level.  (7) Symmetry code: (i) Àx þ 1; Ày; Àz þ 1.

Figure 2
The crystal packing of complex (I).  , 1987, 1988Huang et al., 1991;Marsh, 1989). Only two structures of coordination compounds with dihydroxyoxamidato ligands were found. Both involved anionic mononuclear Ni II complexes with ligands derived from doubly or triply deprotonated oxalodihydroxamic acid. In one of these complexes (Moroz et al., 2006), the dihydroxyoxamidato trianion acts as a simple bidentate chelating ligand forming a square-planar complex. In the second (Ś wią tek-Kozłowska et al., 2000), a square planar Ni II complex again forms, but the dihydroxyoxamidato ligand also forms bridges to the potassium counter-ions generating a polymeric system. The structure presented here is the first example in which a dihydroxyoxamidato anion acts as a bridging ligand between two transition metals. The lack of crystal data for complexes with other transition metal cations may be associated with the ease of hydrolysis of the oxalodihydroxamic acid initiated by a metal salt solution.

Synthesis and crystallization
To the warm mixture containing 0.060 g (0.5 mmol) of oxalodihydroxamic acid and 0.370 g (1 mmol) of Cu(ClO 4 ) 2 Á-6H 2 O in 10 ml of DMSO the solution of 2,2 0 -bipyridine (0.156 g, 1 mmol) in 10 ml of methanol was added upon stirring. The resulted solution was stirred for 1 h and then left for slow evaporation. The resulting blue crystals suitable for X-ray analysis were isolated after one week. The crystals were washed with small amounts of 2-propanol and dried in air, yielding 0.255 g (28%) of the title compound.

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.