Poly[[tetrakis(μ2-pyrazine N,N′-dioxide-κ2 O:O′)neodymium(III)] tris(perchlorate)]

The title three-dimensional coordination network, {[Nd(C4H4N2O2)4](ClO4)3}n, is isostructural to that of other lanthanides. The Nd+3 cation lies on a fourfold roto-inversion axis. It is coordinated in a distorted square-antiprismatic fashion by eight O atoms from bridging pyrazine N,N′-dioxide ligands. There are two unique pyrazine N,N′-dioxide ligands. One ring is located around an inversion center, and there is a twofold rotation axis at the center of the other ring. There are also two unique perchlorate anions. One is centered on a twofold rotation axis and the other on a fourfold roto-inversion axis. The perchlorate anions are located in channels that run perpendicular to (001) and (110) and interact with the coordination network through C—H⋯O 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, and Sun et al. 2004).
The description of the structure of the title compound is part of a series of consecutive papers on three-dimensional  (Sun et al. 2004).
The asymmetric unit of the title compound contains one quarter of a Nd +3 cation, half of two coordinated pyrazine N,N'-dioxide ligands, a quarter of one perchlorate anion, and a half of another perchlorate anion ( Figure 1). The Nd +3 cation lies on a fourfold roto-inversion axis. One ligand (O1, N1, C1, C2) is located around an inversion center, and there is a twofold rotation axis at the center of the other (O2, N2, C3, C4). Both chlorine atoms of the perchlorate anions lie on special positions. Cl1 lies on a fourfold roto-inversion axis, and Cl2 is located on a twofold rotation axis. The high atomic displacement parameters for O4 and O5 bonded to Cl2, and the residual electron density around Cl2 indicate that this perchlorate anion is disordered; however, the disorder does not appear discreet. Only O4 and O5 are easily found in positions that agree with the site symmetry of the anion, therefore only one position was modeled.
The Nd +3 cation is coordinated in a distorted square anti-prismatic fashion by eight O atoms from bridging pyrazine N,N'-dioxide ligands forming a three-dimensional coordination network. The network topology is similar to that which is 4.2CH 3 OH} n in that in can be considered as being composed of two sets of intersecting (4,4) nets (Long et al. 2001). The nets are perpendicular to one another, but they are canted. One set of nets lies parallel to the (1 0 0) plane, and the other set lies parallel to the (0 1 0) plane ( Figure 2).
The title compound forms five unique C-H···O hydrogen bonds ( Figure 3). There are two unique hydrogen bonds between pyrazine N,N'-dioxide ligands and another three hydrogen bonds between the perchlorate anions and pyrazine N,N'-dioxide ligands. The non-disordered perchlorate anion (Cl1 and O3) forms two unique hydrogen bonds with pyrazine N,N'-dioxide ligands resulting in a total of eight hydrogen bonds per ion with the network, but the disordered perchlorate (Cl2, O4, and O5) forms only one unique hydrogen bond with pyrazine N,N'-dioxide ligands resulting in a total of only two hydrogen bonds per ion with the network. As seen in the packing diagrams, the perchlorate anions are located in two sets of supplementary materials sup-2 channels (Figures 4 and 5). In channels that run perpendicular to the (0 0 1) plane only anions containing Cl2 are present. (Figure 4), but in the channels that run perpendiclar to the (1 1 0) plane the anions containing Cl1 and Cl2 alternate ( Figure 5).

Experimental
Pyrazine N,N'-dioxide (0.025 g, 0.223 mmol) was dissolved in deionized water (1.5 ml) and methanol (1.5 ml). An aqueous solution of Nd(ClO 4 ) 3 (0.240 ml of a 0.1167 M solution, 0.028 mmol) was diluted with methanol (0.760 ml) and CH 2 Cl 2 (2.5 ml). The pyrazine N,N'-dioxide solution was layered over the Nd(ClO 4 ) 3 solution, and the two solutions were allowed to slowly mix. Rose colored block-like crystals formed upon the slow evaporation of the resultant solution.

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )