μ-Succinato-bis[aqua(2,2′:6′,2′′-terpyridine)copper(II)] dinitrate dihydrate

The title compound, [Cu2(C4H4O4)(C15H11N3)2(H2O)2](NO3)2·2H2O, was synthesized under hydrothermal conditions. The dinuclear copper complex is located on a crystallographic inversion centre. The CuII ion is pentacoordinated in a tetragonal–pyramidal geometry, with one O atom of a succinate dianion and three N atoms of a 2,2′:6′,2′′-terpyridine ligand occupying the basal plane, and a water O atom located at the apical site. In the crystal structure, O—H⋯O hydrogen bonding links the molecules into a chain parallel to the a axis.

The title compound, [Cu 2 (C 4 H 4 O 4 )(C 15 H 11 N 3 ) 2 (H 2 O) 2 ]-(NO 3 ) 2 Á2H 2 O, was synthesized under hydrothermal conditions. The dinuclear copper complex is located on a crystallographic inversion centre. The Cu II ion is pentacoordinated in a tetragonal-pyramidal geometry, with one O atom of a succinate dianion and three N atoms of a 2,2 0 :6 0 ,2 00 -terpyridine ligand occupying the basal plane, and a water O atom located at the apical site. In the crystal structure, O-HÁ Á ÁO hydrogen bonding links the molecules into a chain parallel to the a axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KJ2141).  (Duangthongyou & Siripaisarnpipat, 2008;He & Huang, 2008;Jin et al., 2008;Li et al., 2009;Liu, 2009;Ke et al., 2009). The succinate dianion has been used as a bridging ligand in the preparation of multinuclear metal complexes. A variety of bridging modes have been found (Ng,1998;Rastsvetaeva et al., 1996;Brusau et al., 2000;He et al., 2007). We report herein the synthesis and crystal stucture of a new succinate complex In the centrosymmetric dinuclear copper complex ( Fig. 1) each of the Cu II ions is pentacoordinated, with one O atom of a succinate dianion and three N atoms of a 2,2':6',2''-terpyridine ligand occupying the basal plane, and a water O atom completing the square-pyramidal geometry from the apical site ( Fig. 1). The atoms N2, N3, N4 and O1 are nearly coplanar, with the maximum deviation from the least-squares plane of 0.0292 (13) Å. The Cu atom is displaced by 0.1281 (11) Å from this plane towards the apical O atom.
With O-H···O hydrogen bonds between the coordinated water molecule and the carboxylate group, (Table 1), a one-dimensional chain running parallel to the a axis is formed as shown in Fig.2. The uncoordinated water provides an extra link and thereby strengthens the chain and also forms a link to the nitrate counterions.

Refinement
The positions of the water H atoms, obtained from a difference Fourier map, were constrained to ideal water geometry and fixed in the final stages of refinement (O-H 0.85 Å), All other H atoms were included in calculated positions, with C-H bond lengths fixed at 0.97 Å (methylene -CH2-) or 0.93Å (aryl group) and were refined in the riding-model approximation. U iso (H) values were calculated at 1.2 U eq (C, O). Fig. 1. The molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

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.
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 Rfactors(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.