Diammonium tetrakis(isothiocyanato)zincate–1,4,10,13,16-hexaoxacyclooctadecane–water (1/2/1)

The title compound, (NH4)2[Zn(NCS)4]·2C12H24O6·H2O, the result of the reaction of ammonium thiocyanate, 18-crown-6 and zinc(II) chloride in aqueous solution, exhibits an unusual supramolecular structure. The Zn atom, two of the thiocyanate chains and a water molecule, disordered over two positions, lie on a mirror plane. The macrocycle adopts a conformation with approximate D 3d symmetry. The ammonium molecules are contained within the bowl of the macrocycle via extensive N—H⋯O hydrogen bonds and the complex molecules are linked via N—H⋯S hydrogen bonds, forming chains along the c-axis direction. The macrocycle is disordered over two positions [refined occupancy ratio = 0.666 (8):0.334 (8)]. The S atoms of two isothiocyanate ligands are disordered within and about the mirror plane.

The title compound, (NH 4 ) 2 [Zn(NCS) 4 ]Á2C 12 H 24 O 6 ÁH 2 O, the result of the reaction of ammonium thiocyanate, 18-crown-6 and zinc(II) chloride in aqueous solution, exhibits an unusual supramolecular structure. The Zn atom, two of the thiocyanate chains and a water molecule, disordered over two positions, lie on a mirror plane. The macrocycle adopts a conformation with approximate D 3d symmetry. The ammonium molecules are contained within the bowl of the macrocycle via extensive N-HÁ Á ÁO hydrogen bonds and the complex molecules are linked via N-HÁ Á ÁS hydrogen bonds, forming chains along the c-axis direction. The macrocycle is disordered over two positions [refined occupancy ratio = 0.666 (8):0.334 (8)]. The S atoms of two isothiocyanate ligands are disordered within and about the mirror plane.

Experimental
Crystal data (NH 4 Table 1 Hydrogen-bond geometry (Å , ). The reaction of ammonium thiocyanate, 18-crown-6 and Zinc (II) chloride in aqueous solution yields the title compound, Fig. 1. All bond lengths and angles are normal and correspond to those reported for (I) (Ramesh et al., 2012).
The C-S [average value of 1.658 (2) Å] and C-N [average value of 1.116 (2) Å] bond lengths indicate the presence of double-bond character. The zinc atom, Zn1, two of the thiocyanate chains [N2-C2-S2 and N3-C3-S3; symmetry code: x, -y + 1/2, z] and the water molecule lie in a mirror plane, except one of the disordered component sulfur atoms, which is inclined at quite an angle to the ac plane. The thiocyanate (N1-C1-S1 = 178.2 (4) °) ligands are almost linear.
The macrocycle adopts a conformation with approximate D 3d symmetry, with all O-C-C-O torsion angles being gauche and alternating in sign, and all C-O-C-C torsion angles being anti.
The sulfur atoms (S2 and S3) of the thiocyanate chains are disordered with large displacement parameters for the S atoms and short C-S bond lengths. The disorder over two positions was modelled and the site occupancies refined to 0.39 (9) and 0.61 (9) for atom S2 and 0.376 (9) and 0.248 (18) for atom S3. The entire crown either molecule is disordered, as detectable from the large displacement parameters for C and O atoms and short C-C and C-O bond lengths. The disorder over two positions was modelled and the site occupancies refined to 0.666 (9) and 0.334 (9) for carbon and oxygen atoms. The water molecule is disordered, as detectable from the large displacement parameters for the O atoms. The disorder over two positions was modelled and the site occupancies refined to 0.425 (15) and 0.575 (15). for carbon and oxygen atoms. The geometry was regularized by soft restraints.
In the crystal, the complex molecules are linked via N-H···S hydrogen bonds forming chains along the c axis (Table 1 and Fig. 2

Experimental
A mixture of 18-crown-6, ammonium thiocyanate and Zinc (II) chloride were dissolved in an aqueous solution in the molar ratio 2:4:1 and thoroughly mixed for two hours to obtain a homogeneous mixture. The solution was allowed to evaporate slowly at ambient temperature. Colourless single crystals suitable for single-crystal X-ray diffraction analysis were obtained in a week.

Refinement
The sulfur atoms (S2 and S3) of the thiocyanate chain are disordered over two positions with refined occupancies of 0.39 (9) and 0.61 (9) for atom S2, and 0.376 (9) and 0.248 (18) for atom S3. The entire crown either molecule is disordered over two positions with refined occupancies of 0.666 (9) and 0.334 (9). The water molecule is disordered over two positions with refined occupancies of 0.425 (15) and 0.575 (15). The corresponding bond distances involving the disordered atoms were restrained to be equal.   A view along the c axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1 for details).
Diammonium tetrakis(isothiocyanato)zincate-1,4,10,13,16-hexaoxacyclooctadecane-water (1/2/1) 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 Occ.