Crystal structure of bis(pyridine-4-carbothioamide-κN 1)bis(thiocyanato-κN)cobalt(II) methanol monosolvate

The crystal structure of the title compound consists of discrete octahedral complexes that are linked by intermolecular N—H⋯S hydrogen bonds into a three-dimensional network that contains channels in which the hydrogen-bonded methanol molecules are located.


Chemical context
Thio-and selenocyanate anions are useful ligands for the synthesis of new coordination compounds and polymers because of their versatile coordination behaviour (Massoud et al., 2013;Kabesova et al., 1995). Compounds in which the metal cations are linked by these ligands are of special interest because magnetic exchange can be mediated (Palion-Gazda et al., 2015;Boeckmann & Nä ther, 2012;Wö hlert et al., 2013). In this context, we are especially interested in cobalt compounds in which the metal cations are octahedrally coordinated by two neutral co-ligands and four anionic ligands. In the corresponding structures, the central cations are linked into chains by mutual pairs of anionic ligands. Some of these compounds show a slow relaxation of the magnetization, which in part can be traced back to single-chain magnetism (Rams et al., 2017a,b;Wö hlert et al., 2012). To study the influence of the neutral co-ligand on the magnetic properties, different pyridine derivatives substituted in the 4-position, e.g. 4-benzoylpyridine, 4-vinylpyridine, 4-(4-chlorobenzyl)pyridine and 4-(3phenylpropyl)pyridine have been investigated (Rams et al., 2017b;Werner et al., 2014Werner et al., , 2015. In this regard, we also became interested in pyridine-4-carbothioamide as a ligand, because in this case the Co(NCS) 2 chains can be linked into layers by pairs of intermolecular hydrogen bonds between the amino H atoms and the thioamide S atom. Unfortunately, the desired compound with composition Co(NCS) 2 (pyridine-4carbothioamide) 2 could not be prepared from solution. Alternatively, we attempted to synthesize discrete solvato complexes as precursors that might transform into the desired compound on thermal annealing, as has been shown ISSN 2056-9890 previously (Boeckmann & Nä ther, 2012). In the course of these investigations, crystals of the title compound were grown and characterized by single crystal X-ray diffraction. Unfortunately, no single-phase crystalline product could be obtained which prevented further investigations.

Structural commentary
The asymmetric unit of the title compound, [Co(NCS) 2 (C 6 H 6 NS) 4 ]ÁCH 3 OH, consists of one Co II cation, two thiocyanate anions, four 4-pyridindethioamide co-ligands and one one methanol molecule, all located in general positions. The Co II cation is sixfold coordinated by two terminal Nbonded thiocyanate anions and four N-bonded pyridine-4carbothioamide ligands, resulting in discrete and slightly distorted octahedra (Fig. 1). The Co-N bond lengths to the thiocyanate anions of 2.0847 (14) and 2.0865 (14) Å are significantly shorter then those to the pyridine N atoms of the pyridine-4-carbothioamide ligand [2.1608 (13)-2.1933 (14) Å ], in agreement with values reported in the literature (Goodgame et al., 2003;Prananto et al., 2017).

Supramolecular features
The discrete complexes are linked into a three-dimensional network by centrosymmetric pairs of intermolecular N-HÁ Á ÁS hydrogen bonds between the amino H atoms and the 4pyridindethioamide S atoms as well as by additional N-HÁ Á ÁS hydrogen bonds involving the thiocyanate S atoms (Fig. 2, Table 1). By this arrangement, channels extending parallel the a axis are formed in which the methanol solvate molecules are located (Fig. 2). The solvent molecules are connected to the network via intermolecular O-HÁ Á ÁS hydrogen bonding between the hydroxyl H atoms and the thiocyanate S atoms (Table 1). It is noted that the methanol molecules also act as acceptors for N-HÁ Á ÁO hydrogen bonding from the amino group of neighbouring complexes. There are also additional short contacts between some of the aromatic hydrogen atoms and the two types of S atoms (thiocyanate, 4-pyridindethioamide), which are indicative of weak C-HÁ Á ÁS interactions (Table 1).

Database survey
There are no structures of cobalt(II) thiocyanate compounds with pyridine-4-carbothioamide as co-ligand reported in the Cambridge Structure Database (Groom et al., 2016). There is only one compound with cadmium, in which the Cd II cations  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
View of the asymmetric unit of the title compound, with atom labelling and displacement ellipsoids drawn at the 50% probability level.
are octahedrally coordinated by two terminal N-bonded pyridinethioamide ligands and four thiocyanate anions. The Cd II cations are linked by pairs of the anionic ligands into linear chains, which corresponds exactly to the structure in which we were originally interested (Neumann et al., 2016).

Synthesis and crystallization
Co(NCS) 2 and pyridine-4-carbothioamide were purchased from Alfa Aesar. Crystals of the title compound suitable for single crystal X-ray diffraction were obtained by the reaction of 8.8 mg Co(NCS) 2 (0.05 mmol) with 27.6 mg pyridine-4carbothioamide (0.2 mmol) in methanol (0.5 ml). The reaction mixture was heated to boiling and then left on the turned-off heating plate to cool down slowly. During this process, crystals of the title compound formed.