Poly[[tris(μ2-4,4′-bipyridine N,N′-dioxide)hexanitratodieuropium(III)] dichloromethane disolvate]

The title one-dimensional coordination network, {[Eu2(NO3)6(C10H8N2O2)3]·2CH2Cl2}n, is isostructural with the previously reported Tb and Tl coordination networks and to its Gd analog. The EuIII cation is coordinated in a distorted tricapped trigonal-prismatic fashion by nine O atoms from three bridging 4,4′-bipyridine N,N′-dioxide ligands and three chelating nitrate anions. None of the atoms lie on a special position, but there is an inversion center located between the rings of one of the ligands. The network topology is ladder-like, and each ladder interacts with six neighboring ladders through C—H⋯O hydrogen bonds. The packing motif of the ladders allows for the formation of channels that run parallel to the a axis; these channels are filled with CH2Cl2 solvent molecules that interact with the ladders through C—H⋯O hydrogen bonds.

The title one-dimensional coordination network, {[Eu 2 (NO 3 ) 6 (C 10 H 8 N 2 O 2 ) 3 ]Á2CH 2 Cl 2 } n , is isostructural with the previously reported Tb and Tl coordination networks and to its Gd analog. The Eu III cation is coordinated in a distorted tricapped trigonal-prismatic fashion by nine O atoms from three bridging 4,4 0 -bipyridine N,N 0 -dioxide ligands and three chelating nitrate anions. None of the atoms lie on a special position, but there is an inversion center located between the rings of one of the ligands. The network topology is ladder-like, and each ladder interacts with six neighboring ladders through C-HÁ Á ÁO hydrogen bonds. The packing motif of the ladders allows for the formation of channels that run parallel to the a axis; these channels are filled with CH 2 Cl 2 solvent molecules that interact with the ladders through C-HÁ Á ÁO hydrogen bonds.

Comment
The synthesis of lanthanide coordination networks has been of recent interest due to the potential of the flexible coordination sphere of the Ln +3 metal ions to produce coordination networks with new, unusual, or high connectivity topologies (Hill et al., 2005;Long et al., 2001;and Sun et al., 2004). Coordination networks with both a high connectivity topology and an open framework have potential for applications in areas such as absorption, ion exchange, or catalysis (Roswell et al., 2004;Rosi et al., 2003;and Seo et al. 2000). Aromatic N,N'-dioxide ligands have been attractive candidates for use with Ln +3 cations as the O-donor atoms of the ligand are complementary to the hard acid character of the lanthanide cations (Cardoso et al., 2001;Hill et al., 2005;Long et al., 2001;Long et al., 2002;and Sun et al., 2004).
The description of the structure of the title compound is part of a set of consecutive papers on one-dimensional ladder-like coordination networks of the type [Ln 2 (NO 3 ) 6 (C 10 H 8 N 2 O 2 ) 3 ] n , with Ln = Eu (this publication) and Gd (Dillner et al., 2010), respectively. Both compounds are also isostructural to the previously reported Tb and Tl coordination networks (Long et al., 2002 andMoitsheki et al., 2006).
The asymmetric unit of the title compound contains one Eu +3 cation, one and a half coordinated 4,4'-bipyridine-N,N'-dioxide ligands, three coordinated nitrate anions, and one solvate CH 2 Cl 2 molecule. None of the atoms lie on a special position, but there is an inversion center located between the rings of one of the ligands (O1, N1, C1-C5). The Eu +3 cation is coordin- Though the Eu +3 cation is nine coordinate, the use of the coordinating nitrate counter ion limits the number of bridging 4,4'-bipyridine-N,N'-dioxide ligands resulting in a one-dimensional coordination network rather than a network with a high connectivity topology. However, the packing motif of the ladders allows for the formation of channels that run parallel to the a-axis; these channels are filled with the CH 2 Cl 2 solvate molecules ( Figure 5). The CH 2 Cl 2 molecules interact with the ladders through C-H···O hydrogen bonding as described above.
The two solutions were allowed to slowly mix. Over a period of several weeks the Eu(NO 3 ) 3 dissolved, and colorless blocklike crystals of the title compound formed.

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.