Di-μ-benzoato-κ3 O,O′:O′;κ3 O:O,O′-bis[aquabis(benzoato-κ2 O,O′)(dimethylformamide-κO)europium(III)]

The title dimeric complex, [Eu2(C7H5O2)6(C3H7NO)2(H2O)2], is centrosymmetric, implying that pairs of equivalent Eu3+ ions and ligands lie trans to each other and that the two Eu3+ ions have exactly the same coordination environment. Each Eu3+ ion is nine-coordinated by two bidentate benzoate ligands, two bridging tridentate chelating benzoate ligands, and one dimethylformamide and one water molecule. The coordination polyhedron of each Eu3+ ion can be described with a distorted monocapped square-antiprismatic geometry. The molecular structure is stabilized by intra- and intermolecular hydrogen bonds between the water molecules and benzoate O atoms.

The title dimeric complex, [Eu 2 (C 7 H 5 O 2 ) 6 (C 3 H 7 NO) 2 (H 2 O) 2 ], is centrosymmetric, implying that pairs of equivalent Eu 3+ ions and ligands lie trans to each other and that the two Eu 3+ ions have exactly the same coordination environment. Each Eu 3+ ion is nine-coordinated by two bidentate benzoate ligands, two bridging tridentate chelating benzoate ligands, and one dimethylformamide and one water molecule. The coordination polyhedron of each Eu 3+ ion can be described with a distorted monocapped square-antiprismatic geometry. The molecular structure is stabilized by intra-and intermolecular hydrogen bonds between the water molecules and benzoate O atoms.

Comment
Because of their excellent luminescent properties (Chin et al., 1994;Singh et al., 2002), rare earth-carboxylic acid complexes have been widely studied and applied in many fields. Distinct structure features with various rare earths (Qiu et al., 2007;Gubina et al., 2000) or ligands (Jin et al., 1996;Wang et al., 2003) have been reported. The title compound, (I) was synthesized and its structure was determined. Similar crystal structure with benzoate as ligands have been reported recently (Ooi et al., 2010).
The centrosymmetric structure of the title complex (I) is shown in Fig. 1 In the crystal structure, intermolecular O7-H7B···O6 ii hydrogen bonds (Table 2) link molecules into chains along the b axis (Fig. 2). The molecular structure is stabilized by intramolecular O7-H7A···O2 i hydrogen bonds (Table 2).
Experimental 0.5 g Eu 2 O 3 (Strem, 99.99%) was dissolved in 5 ml 37% HCl and the solution was evaporated to dryness. 10 ml water was added to the residue and the pH was adjusted to 8 by the addition of NH 3 (aq). The ensuing precipitate was filtered, washed with water and dried. This precipitate was added to a solution containing 1 g C 6 H 5 COOH and 20 ml DMF with stirring.
The mixture was vigorously stirred and filtered. The filtrate was put in a beaker covered with parafilm and left in a dark fume cupboard at room temperature to form colorless needle crystals.

Refinement
All aromatic and methyl H atoms were positioned geometrically with C-H = 0.93 and 0.96 Å, and were constrained to ride on their parent C atoms with U iso (H) = 1.2U eq (C) and 1.5U eq (C), respectively. The DANG and DFIX restraints were used in order to keep the geometry of the water molecule reasonable.
supplementary materials sup-2 Figures Fig. 1. The molecular structure of (I), with atom labels and 50% probability displacement ellipsoids for non-H atoms. The suffix A corresponds to the symmetry code [-x + 1, -y + 1, -z + 1]. Di