catena-Poly[ammonium (cadmium-tri-μ-thiocyanato-κ4 S:N;κ2 N:S)–1,4,10,13,16-hexaoxacyclooctadecane (1/1)]

In the title compound, {(NH4)[Cd(NCS)3]·C12H24O6}n, the Cd2+ ion, the ammonium cation, one of the SCN− ligands and the macrocycle are located on mirror planes. The thiocyanate anions act as bridging ligands between the CdII ions, leading to a polymeric chain arrangement extending along [001] around a twofold screw axis. The ammonium ions are contained within the bowl of the macrocycle via extensive N—H⋯O hydrogen bonding.

In the title compound, {(NH 4 )[Cd(NCS) 3 ]ÁC 12 H 24 O 6 } n , the Cd 2+ ion, the ammonium cation, one of the SCN À ligands and the macrocycle are located on mirror planes. The thiocyanate anions act as bridging ligands between the Cd II ions, leading to a polymeric chain arrangement extending along [001] around a twofold screw axis. The ammonium ions are contained within the bowl of the macrocycle via extensive N-HÁ Á ÁO hydrogen bonding.
A perspective view of compound (I) with the atom-numbering scheme is shown in Fig. 1 (Gu et al., 2011). The values of the bond angles around cadmium are close to those expected for a regular octahedral geometry, the largest angular deviation being observed for the N2 -Cd1-N1 angle [93.34 (5)°].
The parameters of hydrogen bonds are given in the Table 1. The thiocyanate anions function as bridging ligands between the CdII centres, leading to a chain-like arrangement are parallel to one another and expanding along [001]. The ammonium molecules also participate in extensive N-H···O hydrogen bonding, as shown in Fig. 2.

Experimental
The mixture of 18-crown-6 (C 12 H 24 O 6 ), CdCl 2 and NH 4 SCN (molar ratio 1:1:3) were thoroughly dissolved in double distilled water and stirred for 5 h to obtain a homogeneous mixture. The colorless single crystals were obtained after the filtrate had been allowed to stand at room temperature for three weeks.

Refinement
Carbon H atoms were placed geometrically (C-H = 0.97 Å) and treated as riding with U iso (H) = 1.2U eq (C). Water H atoms were located in calculated positions and treated in the subsequent refinement as riding atoms, with N-H = 0.89 Å and U iso (H) = 1.5U eq (O).

Figure 1
The molecular structure of the title compound with the atom numbering scheme and 50% probability displacement ellipsoids. H atoms are presented as a small spheres of arbitrary radius.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.003 Δρ max = 0.20 e Å −3 Δρ min = −0.36 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0058 (2) Absolute structure: Flack (1983), 7607 Friedel pairs Flack parameter: 0.005 (15) 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.