Tetra-μ-benzoato-κ4 O:O′;κ3 O:O,O′;κ3 O,O′:O′-bis[(benzoato-κ2 O,O′)(1,10-phenanthroline-κ2 N,N′)europium(III)] benzoic acid disolvate

The asymmetric unit of the title complex, [Eu2(C7H5O2)6(C12H8N2)2]·2C6H5COOH, contains one-half of the complex molecule, the complete molecule being generated by inversion symmetry, and one benzoic acid solvent molecule. The two EuIII ions are linked by four bridging benzoate ions, with an Eu⋯Eu distance of 3.96041 (12) Å. Each EuIII ion is coordinated by one phenanthroline heterocycle and a bidentate benzoate ion. The irregular nine-coordinated geometry of the metal ion is composed of seven O and two N atoms. The molecular structure is stabilized by intramolecular C—H⋯O hydrogen bonds. In the crystal structure, molecules are linked into chains by intermolecular C—H⋯O hydrogen bonds along the a axis. The crystal structure is further stabilized by intermolecular C—H⋯O and C—H⋯π interactions. Weak π–π interactions are also observed [centroid–centroid distances = 3.6962 (10)–3.6963 (10) Å].

The asymmetric unit of the title complex, [Eu 2 (C 7 H 5 O 2 ) 6 -(C 12 H 8 N 2 ) 2 ]Á2C 6 H 5 COOH, contains one-half of the complex molecule, the complete molecule being generated by inversion symmetry, and one benzoic acid solvent molecule. The two Eu III ions are linked by four bridging benzoate ions, with an EuÁ Á ÁEu distance of 3.96041 (12) Å . Each Eu III ion is coordinated by one phenanthroline heterocycle and a bidentate benzoate ion. The irregular nine-coordinated geometry of the metal ion is composed of seven O and two N atoms. The molecular structure is stabilized by intramolecular C-HÁ Á ÁO hydrogen bonds. In the crystal structure, molecules are linked into chains by intermolecular C-HÁ Á ÁO hydrogen bonds along the a axis. The crystal structure is further stabilized by intermolecular C-HÁ Á ÁO and C-HÁ Á Á interactions. Weakinteractions are also observed [centroid-centroid distances = 3.6962 (10)-3.6963 (10) Å ]. H atoms treated by a mixture of independent and constrained refinement Á max = 0.62 e Å À3 Á min = À0.44 e Å À3 Table 1 Selected bond lengths (Å ).  Table 2 Hydrogen-bond geometry (Å , ).

metal-organic compounds
Cg1 is the centroid of the C35-C40 benzene ring. The asymmetric unit of the title complex (I) (Fig. 1) consists of one-half of the complex molecule and one benzoic acid.
The complex molecule lies on a crystallographic inversion center. The two europium(III) ions are linked by four benzoate ions, with an Eu-Eu distance of 3.96041 (12) Å. Among the four benzoate ions, two of them also behave as chelating ligands to the europium(III) ions. Each metal ion is coordinated by one phenanthroline heterocycle and a bidentate benzoate ion. The irregular nine-coordinated geometry of the europium(III) ion is completed by seven benzoate O atoms and two phenanthroline N atoms. Bond lengths of Eu-O and Eu-N are listed in Table 1. All other bond lengths and angles are comparable to a closely La-benzoato complex (Shi et al., 2001).
Experimental 0.5 mmol of EuCl 3 .6H 2 O was dissolved in methanol and then was added into a solution (methanol-H 2 O, 1.5:1) of 1,10phenanthroline (0.5 mmol) and benzoic acid (1.5 mmol). The mixture was sealed in a tube, and heated directly to 403 K.
After keeping at 403 K for 2 days, it was cooled to room temperature. Colourless block crystals (I) were obtained by filtration, and was washed with water and ethanol.

Refinement
The H1O8 hydrogen atom was located from difference Fourier map and refined freely. All aromatic hydrogen atoms were placed in their calculated positions, with C-H = 0.93 Å, and refined using a riding model with U iso = 1.2 U eq (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 > 2sigma(F 2 ) is used only for calculating R-factors(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )