Crystal structure of catena-poly[[[bis(pyridine-4-carbothioamide-κN 1)cadmium]-di-μ-thiocyanato-κ2 N:S;κ2 S:N] methanol disolvate]

The crystal structure of the title compound consists of CdII cations that are linked by thiocyanato anions into chains which are further connected into layers by intermolecular N—H⋯O and O—H⋯S hydrogen bonding via additional methanol molecules.


Chemical context
Thiocyanato anions are versatile ligands that can coordinate to metal cations in different ways . In this context, compounds in which paramagnetic metal cations are linked into chains by -1,3 bridging anionic ligands are of special interest, because they can show different magnetic behavior (Palion-Gazda et al., 2015). This is the case e.g. for compounds of general composition M(NCS) 2 (L) 2 (M = Mn, Fe, Co and Ni; L = pyridine derivative) that frequently show cooperative magnetic properties like ferromagnetic or antiferromagnetic ordering or a slow relaxation of the magnetization indicative for single chain magnetic behavior Wö hlert et al., 2011;Boeckmann & Nä ther, 2012;Werner et al., 2015a,b). Unfortunately, compounds with a bridging coordination are frequently less stable than those in which these anionic ligands are only N-terminally coordinating. Hence, we have developed an alternative synthesis procedure which is based on thermal decomposition of suitable precursor compounds and leads directly to the formation of the desired compounds . However, following this procedure only microcrystalline materials are obtained. This is the reason why we are also interested in the diamagnetic cadmium analogues. This metal cation is much more chalcophilic than most paramagnetic cations, which means that the desired compounds with a bridging coordination of the anionic ligands can easily be crystallized and characterized by single crystal X-ray diffrac-tion . In several cases, the resulting structures are isotypic to the paramagnetic analogues and therefore the latter can be refined by the Rietveld method using the crystallographic data of the respective Cd II compound . In the scope of our systematic work, we became interested in pyridine-4-carbo-thioamide as another ligand that was reacted with cadmium(II) thiocyanate to give the title compound.

Structural commentary
The asymmetric unit of the title compound, [Cd(NCS) 2 (C 6 H 6 N 2 S)]Á2CH 3 OH, consists of a Cd II cation that is located on a centre of inversion as well as one thiocyanato anion, one pyridine-4-carbothioamide ligand and one methanol molecule in general positions. The Cd II cation is sixfold coordinated by two N-bonding pyridinethioamide ligands as well as two N-and two S-coordinating thiocyanate anions in an all trans distorted octahedral environment (Fig. 1). As expected, the Cd-N bond length to the negatively charged thiocyanate anion is significantly shorter than to the pyridine-4-carbothioamide N atom; the Cd-S bond length is within the normal range (Table 1). The Cd II cations are linked by centrosymmetric pairs of anionic ligands into chains along [010] (Fig. 2). The methanol molecule is equally disordered over two orientations.

Figure 1
The coordination of the Cd II cation in the structure of the title compound; the two orientations of the methanol solvent molecule are shown. Displacement ellipsoids are drawn at the 50% probability level.

Figure 2
View of a Cd-thiocyanate chain in the crystal structure of the title compound.

Supramolecular features
In the crystal structure, the neutral chains are linked into layers extending along (201) Table 2). The hydrogen-bonding geometry is very similar for the two disordered and slightly differently oriented methanol molecules (Table 2). This arrangement leads to 12-membered rings [graph-set notation R 4 4 (12); Etter et al., 1990] in which four donor and four acceptors are involved ( Fig. 2 and Table 2). There are additional C-HÁ Á ÁN, C-HÁ Á ÁS and N-HÁ Á ÁS interactions of much weaker nature that consolidate the three-dimensional network (Table 2).

Figure 3
View of one layer in the crystal structure of the title compound with hydrogen bonds shown as dashed lines. Only one orientation of the disordered methanol molecule is shown. The white residue of BaSO 4 was filtered off and the resulting solution dried at 353 K. The homogeneity of the product was checked by X-ray powder diffraction and elemental analysis. The title compound was obtained by reaction of 11.4 mg Cd(NCS) 2 (0.05 mmol) with 27.6 mg pyridine-4-carbothioamide (0.2 mmol) in boiling methanol (2 ml). Crystals suitable for single-crystal x-ray diffraction formed after cooling.

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-H, O-H and N-H hydrogen atoms were located in a difference map but were positioned with idealized geometry (methyl and O-H hydrogen atoms allowed to rotate but not to tip) and were refined with U iso (H) = 1.2U eq (C, N) (1.5 for methyl and O-H hydrogen atoms) using a riding model with C-H = 0.95 Å for aromatic, C-H = 0.98 Å for methyl, N-H = 0.88 Å and O-H = 0.84 Å , respectively. The methanol molecule is equally disordered over two orientations and was refined using a split model using SAME restraints (Sheldrick, 2015).

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.

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