A trinuclear cobalt–cerium complex: bis(2,2′-bipyridine)-1κ2 N,N′;3κ2 N,N′-hexa-μ-methacrylato-1:2κ6 O:O′;2:3κ6 O:O′-nitrato-2κ2 O,O′-2-cerium(III)-1,3-dicobalt(II)

In the title trinuclear cobalt-cerium complex, [CeCo2(C4H5O2)6(NO3)(C10H8N2)2], the CeIII and each of the two CoII ions are bridged by three bidentate methacrylate ligands. The CeIII center is coordinated by six O atoms from six methacrylate ligands and two O atoms from the nitrate anion in a distorted square-antiprismatic geometry. Each CoII ion is coordinated by three O atoms from three methacrylate ligands and two N atoms from a 2,2′-bipyridine ligand in a distorted trigonal-pyramidal geometry. In the crystal structure, π–π interactions between the aromatic rings [centroid–centroid distances of 3.816 (8) and 3.756 (8) Å] link the molecules into chains propagated in [01]. Weak intermolecular C—H⋯O hydrogen bonds further stabilize the crystal packing.


Comment
As a contribution to a structural study of heterometallic complexes containing d-transition metal and rare-earth(III) cations (Wu & Guo, 2004;Zhu et al., 2004a,b;Zhu et al., 2005), herewith we report the synthesis and crystal structure of the title compound.
The crystal structure of the title Co-Ce-Co trinuclear complex is similar to the known crystal structures of the Zn-Nd-Zn, Zn-Pr-Zn, Zn-La-Zn and Zn-Ce-Zn complexes (Wu & Guo, 2004;Zhu et al., 2004a,b;Zhu et al., 2005). The Ce III center is coordinated by six O atoms from six methacrylato ligands and two O atoms from nitrate anion in a distorted square-antiprismatic geometry. Each Co II ion is coordinated by three O atoms from three methacrylato ligands and two N atoms from 2,2'-bipyridine ligand in a distorted pyramidal geometry. The Ce III and each of two Co II ions are bridged by three bidentate methacrylato ligands. Two Ce···Co separations are almost equal being 3.944 (1) and 3.993 (1) Å, respectively.
In the crystal structure, π-π interactions between the aromatic rings (Table 1) (Table 2) stabilize further the crystal packing.

Experimental
CeL 3 .2H 2 O (870 mg, 2.0 mmol; HL = CH 2 C(CH 3 )COOH ) prepared in accordance with Lu et al. (1995) and Co(NO 3 ) 2 .6H 2 O (435 mg, 1.5 mmol) were dissolved in 15 ml H 2 O, and the pH adjusted to 4.0 using HL. Three mililiters of ethanol solution 2,2'-bipyridine (234 mg, 1.5 mmol) were added into the mixed solution with stirring. After filtration, the filtrate was allowed to stand at room temperature and single crystals suitable for X-ray work were obtained after two weeks.

Refinement
All H-atoms were placed in idealized locations with C-H distances 0.93 -0.96 Å and refined as riding with U iso (H) = 1.2 or 1.5 U iso (C). Fig. 1

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.