catena-Poly[[[bis(thiourea-κS)cadmium]-di-μ-thiocyanato-κ2 N:S;κ2 S:N] dihydrate]

The title compound, {[Cd(NCS)2(CH4N2S)2]·2H2O}n, forms a one-dimensional chain parallel to the a axis, caused by the presence of the bridging thiocyanate groups. Two solvent molecules per complex are present in the lattice. The CdII ion is situated on an inversion centre and is coordinated in a distorted octahedral fashion by two N and two S atoms from four thiocyanate ligands and by two S atoms from two thiourea molecules. Weak O—H⋯S, N—H⋯O and N—H⋯N interactions reinforce the structure.

The title compound, {[Cd(NCS) 2 (CH 4 N 2 S) 2 ]Á2H 2 O} n , forms a one-dimensional chain parallel to the a axis, caused by the presence of the bridging thiocyanate groups. Two solvent molecules per complex are present in the lattice. The Cd II ion is situated on an inversion centre and is coordinated in a distorted octahedral fashion by two N and two S atoms from four thiocyanate ligands and by two S atoms from two thiourea molecules. Weak O-HÁ Á ÁS, N-HÁ Á ÁO and N-HÁ Á ÁN interactions reinforce the structure.
The cadmium atom in catena-Poly [[[bis(thiourea-κS)cadmium]-di-µ-thiocyanato-κ 2 N:S;κ 2 S:N] dihydrate] is located at the inversion center and is octahedrically coordinated by two S atoms and two N atoms from four thiocyanate groups as well as by two S atoms from thiourea molecules. The neighbouring Cd II ions are bridged by two µ-SCN-κ 2 N:S ligands, thus forming eight-membered ring of [Cd-SCN] 2 type with the Cd···Cd distance of 5.853 Å, which is close to the values observed in other bridged systems (Machura et al., 2011). These units form one-dimensional chains of slightly distorted edge-shared Cd-centered octahedra along the [100] crystallographic direction. The Cd-S i Cd-N distances are typical for cadmium(II) thiocyanate complexes. The IR spectra clearly show the presence of the thiocyanato groups (with the maxima of ν CN absorption at 2078 cm -1 ).
In the structure of [[Cd{SC(NH 2 ) 2 } 2 (SCN) 2 ] . 2H 2 O] n , several weak interactions may be assumed, leading to the alternating arrangement of water and complex molecules. Each water molecule interacts with S or N atoms from the three neighboring polymeric chains. Thus, it can serve as a donor of a weak hydrogen bond to the sulfur atom from one of the thiourea moieties (O1(H1D)-S1 viii ) in one chain, as well as to sulfur from one thiocyanato ligand (O1(H1C) -S2) in the other. The oxygen lone pairs act as acceptors towards NH 2 groups from thiourea moieties located within the third chain (N2(H2B) -O1 vii , N1(H1A) -O1 v , N2(H2A)-O1 v ). Finally, one "interchain" interaction, N1-H1B···N3 i , operates between NH 2 and SCN groups.

Experimental
The reaction was carried out between 0.50 g cadmium(II) thiocyanate, Cd(SCN) 2 , and 1.34 g thiourea (molar ratio 1:8) which were dissolved in a small amount of water. The mixture was heated to 70°C and stirred using magnetic stirrer for 50 minutes and then left for crystallization at room temperature. After a few days two types of crystals appeared in the flask: needles (0.2 g) and blocks (0.1 g), which were mechanically separated under the microscope. The structure of needle-like crystals [Cd(SCN) 2 {µ-SC(NH 2 ) 2 }] n (m.p. 189°C) has been already described (Wang et al., 2002), while the block-like crystals appeared to be a new compound, crystallizing as diaqua solvate [[Cd{SC(NH 2 ) 2 } 2 (SCN) 2 ].2H 2 O] n (m.p. 187°C). The product, when taken from the mother liquor and dried using the filter paper, changes -becomes opaque and finally takes the form of a powder (most probably because of the removal of the solvent molecules). IR spectra were recorded using Mattson Genesis II Gold spectrometer equipped with Momentum Microscope as detector.

Refinement
All N-H atoms were placed in calculated positions and refined as riding on their carrier atoms with N-H = 0.86 Å (NH 2 ) and U iso (H) = 1.2 times U eq (N). Solvent O-H hydrogen atoms were found in the Fourier map and refined as constrained to: O-H bond length of 0.80 Å, H1C -H1D distance of 1.30 Å and U iso (H) = 1.5 times U eq (O) with the default uncertainties.

Computing details
Data collection: CrysAlis PRO (Oxford Diffraction, 2008); cell refinement: CrysAlis PRO (Oxford Diffraction, 2008); data reduction: CrysAlis PRO (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: WinGX (Farrugia, 1999) and publCIF (Westrip, 2010).    where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.47 e Å −3 Δρ min = −0.51 e Å −3 Special details Experimental. CrysAlisPro, (Oxford Diffraction, 2008). Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by (Clark & Reid, 1995). Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.