Bis(μ-1,2-bis{[2-(2-pyridyl)-1H-imidazol-1-yl]methyl}benzene)bis[bis(thiocyanato-κN)cadmium(II)]

The asymmetric unit of the binuclear title compound, [Cd2(NCS)4(C24H20N6)2], contains one half-molecule, consisting of one Cd2+ cation, two half 1,2-bis{[2-(2-pyridyl)-1H-imidazol-1-yl]methyl}benzene (L) ligands and two SCN− anions. The dimeric cyclic molecule is completed by crystallographic inversion symmetry. The Cd2+ cation is coordinated by two N atoms from two SCN− anions and four N atoms from two symmetry-related L ligands, exhibiting a distorted octrahedral coordination. A two-dimensional supramolecular network stacked parallel to [210] is finally formed by linking these dimers through weak π–π stacking interactions between the pyridine rings and benzene rings of adjacent dimers, with a plane-to-plane distance of 3.36 (6) Å and a centroid–centroid distance of 3.67 (2) Å. One of the thiocyanate S atoms is equally disordered over two positions.

The asymmetric unit of (I) contains one Cd 2+ cation, two halfs of the L ligand and two SCNanions. Two complete L ligands link two Cd 2+ cations to form a centrosymmetric dimeric ring. So the asymmetric unit contains only half of the ring molecule (Fig. 1). The Cd 2+ cation is coordinated to the N atom of two SCNanions and four N atoms from symmetry-related L ligands within normal Cd-N distances (Dai et al., 2002;Luan et al., 2006;Wang et al., 2003). The resulting CdN 6 polyhedron can be considered as a distorted octahedron. Each dimer links adjacent dimers via π-π interactions between pyridine rings and benzene rings to form a 2D supramolecular network stacked along [210] (Fig. 2), with a plane to plane distance of 3.36 (6) Å and a centroid-centroid distance of 3.67 (2) Å.

S2. Experimental
A mixture of Cd(OAc) 2 . 2H 2 O (0.13 g, 0.50 mmol), L (0.2 g, 0.5 mmol), KSCN (0.10 g, 1 mmol) and H 2 O (10 ml) was stirred for 1 h, and then transferred and sealed in a 25 ml Teflon-lined stainless steel container. The container was heated to 423 K, held at that temperature for 72 h, and cooled to room temperature at a rate of 10 Kh -1 . Colourless parallelepipeds of (I) were collected in 78% yield.

S3. Refinement
One of the SCNgroups is disordered over two positions. The S atom was refined with a 0.5:0.5 occupancy ratio. All H atoms on C atoms were positioned geometrically and refined as riding atoms, with C-H = 0.93 Å for aromatic C atoms, and with C-H = 0.97 Å for aliphatic C atoms, and U iso =1.2 or 1.5U eq (C).

Figure 1
A displacement ellipsoids view of (I), drawn at 30% probability level, showing two cations and one anion. All nonlabelled atoms are generated by symmetry operator: 2-x, y, 1-z. H atoms were omitted for clarity. The two orientations of the disordered thiocyanate anion are shown.

Figure 2
View of the two-dimensional supramolecular structure formed by π-π stacking interactions (red dashed lines).

Bis(µ-1,2-bis{[2-(2-pyridyl)-1H-imidazol-1-yl]methyl}benzene)bis[bis(thiocyanato-κN)cadmium(II)]
Crystal data [Cd 2 (NCS) 4 (C 24 H 20 N 6 ) 2 ] M r = 1242.04 Monoclinic, P2 1 /n Hall symbol: -P 2yn a = 10.1170 (5)   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.70 e Å −3 Δρ min = −0.56 e Å −3 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.