catena-Poly[di-μ1,1-azido-(1,10-phenanthroline)cadmium(II)]

The asymmetric unit of the title CdII compound, [Cd(N3)2(C12H8N2)]n, contains a CdII atom, located on a twofold axis passing through the middle of the phenanthroline molecule, one azide ion and half of a 1,10-phenanthroline molecule. The CdII atom exhibits a distorted octahedral coordination including one chelating 1,10-phenanthroline ligand and four azide ligands. The crystal structure features chains along the c direction in which azide groups doubly bridge two adjacent CdII atoms in an end-on (EO) mode. Interchain π–π stacking interactions, with centroid–centroid separations of 3.408 (2) Å between the central aromatic rings of 1,10-phenanthroline molecules, lead to a supramolecular sheet parallel to the bc plane.


Experimental
Crystal data [Cd(N 3

Comment
Many compounds with uncommon magnetic properties have been widely investigated by using azido ligand, resulting from its rich coordination fashions (Ribas et al., 1999;Gao et al., 2004). The azido ligand exhibits a variety of bridging modes such as bi-dentate end-on (EO) and end-to-end (EE) bridging fashions (Liu et al., 2007;Cano et al., 2005;Goher et al., 2008;Mautner et al., 2010). A number of compounds with various structures have been obtained by introducing auxiliary ligands to the metal-azido system (Abu-Youssef et al., 2000;Bose et al., 2004;Meyer et al., 2005). The present example shows an infinite wavelike chain compound with 1,10-phenanthroline as an auxiliary ligand, [Cd(N 3 ) 2 (C 12 H 8 N 2 )], in which azido ligand adopts the EO mode.
The asymmetric unit of the title compound contains half a Cd II ion, one azido ion and half a 1,10-phenanthroline molecule ( Fig. 1). The Cd II ion exhibits a distorted octahedral geometry, coordinated by one chelating 1,10-phenanthroline ligand and four azido ligands with the end-on (EO) mode. The distances of Cd-N vary from 2.306 (2) to 2.411 (3) Å . The azido ligands doubly bridge neighbouring Cd II centers in the EO fashion, yielding an infinite wave-like Cd II -azido chain along the c direction with the shortest Cd···Cd separation being 3.764 (3) Å.
The adjacent Cd II -azido chains are mediated by interchained π-π stacking interactions between the aromatic rings of 1,10phenanthroline molecules, which arrange in the opposite direction alternatively. The centroid-to-centroid distance between the central rings of the phenanthroline is 3.408 (2)Å and the centroid-to-plane distance is 3.28 Å leading to a slippage of 0.936Å. This π-π stacking builts up a 2-D supramolecular layer parallel to the bc plane (Fig. 2).

Refinement
Hydrogen atoms were allowed to ride on their respective parent atoms with C-H distances of 0.93 Å, and were included in the refinement with isotropic displacement parameters U iso (H) = 1.2U eq (C).

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.