Poly[bis(μ2-1,3-phenylenediamine-κ2 N:N′)di-μ-thiocyanato-κ2 N:S;κ2 S:N-cadmium]

The structure of the title polymeric compound, [Cd(SCN)2(C6H8N2)2]n, exhibits a two-dimensional staircase-like structure parallel to (010) in which the CdII atom lies on a twofold rotation axis and has a distorted octahedral CdS2N4 geometry involving four μ-1,3-(SCN) group donors and two N-atom donors from 1,3-phenylenediamine ligands, which also have twofold symmetry. The major contributions to the cohesion and the stability of this two-dimensional polymeric structure are the covalent Cd—S,N bonds and one weak intralayer N—H⋯S hydrogen bond.

The structure of the title polymeric compound, [Cd(SCN) 2 -(C 6 H 8 N 2 ) 2 ] n , exhibits a two-dimensional staircase-like structure parallel to (010) in which the Cd II atom lies on a twofold rotation axis and has a distorted octahedral CdS 2 N 4 geometry involving four -1,3-(SCN) group donors and two N-atom donors from 1,3-phenylenediamine ligands, which also have twofold symmetry. The major contributions to the cohesion and the stability of this two-dimensional polymeric structure are the covalent Cd-S,N bonds and one weak intralayer N-HÁ Á ÁS hydrogen bond.

Comment
The crystal engineering of inorganic-organic hybrid coordination polymers is currently one of the most active fields in coordination chemistry, supramolecular and materials chemistry. These compounds attract significant attention for their architectures and topologies (Yang et al., 2001), including a large number of extended assemblies such as helical network (Withersby et al., 1997;Chemli et al. 2013) molecular zippers, diamondoid, honeycomb (Tong et al., 1998), square-grid (MacGillivary et al., 1994), T-shaped and ladder frameworks. (Fujita et al., 1995;Blake et al.,1997). Hybrid inorganicorganic thiocyanate materials exhibit interesting physical properties such electrical conductivity and dielectric relaxation process (Karoui et al., 2013) and may have potential applications in non-linear optics and luminescence (Chen et al., 2000;Bai et al., 2011). Herein we report the structure of a new polymeric hybrid [Cd(SCN) 2 (C 6 H 8 N 2 ) 2 ] n . As shown in Fig.   1, each cadmium atom, which sits on a twofold rotation axis, is coordinated by two cis N-bonded and two cis S-bonded thiocyanato anions. Two trans-coordinated neutral m-phenylenediamine ligands complete the octahedral coordination geometry around cadmium. The crystal structure of the title compound consists of both doubly µ-1,3-SCN and µ-1,3phenylendiamine -bridged two-dimensional networks (Fig. 2). In the CdN4S2 core, the Cd-N and Cd-S bonds are in the range 2.3061 -2.364 (3) Å and 2.7143 (10) Å, respectively (Table 1). The bond angles involving the cadmium (II) atom range from 83.89 (11) to 96.91 (10)° and from 174.75 (8) to 178.87 (14)°. These values are in good agreement with those observed in other similar complexes (Chemli et al. 2013). The double SCN bridging mode gives rise to a centrosymmetrical eight-membered Cd(SCN) 2 Cd rings in a chair conformation because of the almost linear SCN groups (S-C-N angle = 178.8 (3)°). The distance between adjacent Cd atoms in Cd 2 (SCN) 2 rings is 5.937 Å. Again, these rings built up a staircase-like chain through their corner-sharing action at the two cadmium atoms via the µ-1,3-phenylenediamine moiety and give rise to twenty-membered [Cd 4 (µ-1,3-SCN) 4 (µ-1,3-phenylendiamine) 2 ] macrocycles as subunits, as depicted in Fig. 2. The bond angles in the phenyl groups deviate significantly from the idealized value of 120° due to the effect of the substituent. In fact, it was established that the angular deformations of phenyl groups can be described as a sum of the effects of the different substituents (Domenicano & Murray-Rust, 1979). The phenyl rings of 1,3-phenylendiamine ligand are planar with the greatest deviation from the six-atoms least-square plane of 0.0001 Å. They are well ordered with C-C-C angles in agreement with the expected sp 2 hybridization. The π-π interactions between neighboring phenyl rings may be neglected (>4 Å). The major contributions of the cohesion and the stability of this polymeric structure is assured by the covalent Cd-(S,N) bonds and the presence of one weak intralayer N-H···S hydrogen bond with the H···S and N···S distances of 2.674 Å and 3.589 (3) Å, respectively (

Experimental
To 25 ml of an aqueous solution of thiocyanic acid (0.4 mol.l -1 ) prepared using the published procedure (Bartlett et al., 1969) an appropriate amount of cadmium carbonate (0.832 g, 5 mmol) was added and refluxed for 2 h. After cooling, 25 ml of methanol and 0.7 ml of a solution of 1,3-phenylenediamine (7.5 mol.l -1 ) was added. The resulting solution was heated under reflux for 2 h and left at ambient temperature for 2 hours after which well shaped brown crystals were obtained on slow evaporation of the solvent. They were washed with diethyl ether and dried over P 2 O 5 .

Refinement
All H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.95-0.98 Å, N-H = 0.92 Å, and with U iso (H) = 1.2U eq (C, N).

Figure 2
The two-dimensional molecular structure of the title coordination polymer showing the staircase molecular arrangement.

Poly[bis(µ 2 -1,3-phenylenediamine-κ 2 N:N′)di-µ-thiocyanato-κ 2 N:S;κ 2 S:N-cadmium]
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.60 e Å −3 Δρ min = −0.58 e Å −3 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq