Crystal structure of bis(acetonitrile-κN)bis(4-benzoylpyridine-κN)bis(thiocyanato-κN)cobalt(II)

The crystal structure of the title compound consists of discrete octahedral complexes, that are linked by intermolecular C—H⋯O and C—H⋯S hydrogen bonding into layers.


Chemical context
In recent times, the synthesis of materials exhibiting cooperative magnetic properties has still been a topic of major interest in coordination chemistry (Zhang et al., 2011). A good approach for the preparation of such compounds is the use of small anionic ligands such as e.g. thiocyanate anions to link paramagnetic cations, enabling a magnetic exchange between the cations (Palion-Gazda et al., 2015;Massoud et al., 2013). During the last few years, our group has reported on a number of coordination polymers with thiocyanato ligands that show different magnetic phenomena, including a slow relaxation of the magnetization (Werner et al., 2014(Werner et al., , 2015a. In the course of this project, we became interested in compounds based on 4-benzoylpyridine, for which at that time only three thiocyanato compounds had been reported (Drew et al., 1985;Soliman et al., 2014;Bai et al., 2011). During these investigations, we obtained a compound with composition [Co(NCS) 2 (4-benzoylpyridine) 2 ] in which the Co II cations are linked by pairs of anionic ligands into chains. In contrast to all other such chain compounds where all ligands are always trans-coordinating, in this compound a cis-coordination of the N and the S atoms of the thiocyanate anions was observed (Rams et al., 2017). Therefore, we assumed that this compound might be metastable and that a second modification with the usual trans-coordination could be prepared by thermal annealing of precursors with terminal N-bonded thiocyanate anions. In this context, it is noted that there are many examples where different modifications or isomers have been obtained by this alternative route (Werner et al., 2015a,c;Suckert et al., 2016). In the course of these studies, crystals of the title compound, [Co(NCS) 2 (C 2 H 3 N) 2 (C 12 H 9 NO) 2 ], were obtained and characterized by single crystal X-ray diffraction. Unfortunately, no pure crystalline powder could be obtained, which prevented further investigations of the thermal properties of this compound.

Structural commentary
The asymmetric unit of the title compound consists of one cobalt(II) cation, one thiocyanato anion, one acetonitrile molecule and one neutral 4-benzoylpyridine ligand. The cobalt(II) cation is located on a center of inversion while the thiocyanato anion, the acetonitrile molecule and the 4-benzoylpyridine ligand are located in general positions. The Co II cation is octahedrally coordinated by the N atoms of two terminal anionic ligands, two acetonitrile molecules and two 4-benzoylpyridine ligands (Fig. 1). As expected, the Co-N bond lengths to the thiocyanate anions are significantly shorter [2.0520 (15) Å ] than those to the pyridine N atom of the neutral 4-benzoylpyridine ligand [2.1831 (13) Å ]. All bond lengths are in agreement with values reported in the literature (Drew et al., 1985;Soliman et al., 2014). The 4-benzoylpyridine ligand is not planar; the dihedral angle between the phenyl and pyridine rings is 55.37 (8) . This is in agreement with values retrieved from the literature, which vary between 40.4 and 74.3 (Escuer et al., 2000(Escuer et al., , 2004.

Supramolecular features
In the crystal structure of the title compound, the discrete complexes are linked by intermolecular C-HÁ Á ÁO hydrogen bonds between one of the pyridine ring H atoms and the oxygen atom of the 4-benzoylpyridine ligand of a neighboring complex into dimers, which are further connected into chains (Fig. 2, Table 1). These chains are further linked into layers parallel to (101) by centrosymmetric pairs of intermolecular C-HÁ Á ÁS hydrogen bonds between one of the acetonitrile hydrogen atoms and the neighbouring thiocyanato S atom (Fig. 3, Table 1). Pronounced intermolecular interactions are not observed between these layers.

Database survey
To the best of our knowledge, there are only three coordination compounds with thiocyanato ligands and with 4-benzoylpyridine reported in the Cambridge Structural Database (Version 5.38, last update 2016; Groom et al., 2016). In two of these structures, Co II or Ni II cations are octahedrally coordinated by four 4-benzoylpyridine ligands and two thiocyanate anions (Drew et al., 1985;Soliman et al., 2014). In the third compound, Cu II cations are coordinated in a squareplanar mode by two 4-benzoylpyridine ligands and two thiocyanate anions (Bai et al., 2011). A general search for coordination compounds with 4-benzoylpyridine resulted in 22 structures including the aforementioned ones. One of these compounds consists of Mn II cations that are octahedrally coordinated by two 4-benzoylpyridine ligands as well as by four 1,3 -bridging azido ligands and linked into chains by the anionic ligands (Mautner et al., 2015).

Synthesis and crystallization
Co(NCS) 2 and 4-benzoylpyridine were purchased from Alfa Aesar. Crystals of the title compound suitable for single crystal X-ray diffraction were obtained by the reaction of 26.3 mg Co(NCS) 2 (0.15 mmol) with 55.0 mg 4-benzoylpyridine (0.3 mmol) in acetonitrile (1.5 ml) after a few days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were positioned with idealized geometry and were refined with fixed isotropic displacement parameters U iso (H) = 1.2U eq (C) for aromatic and U iso (H) = 1.5 U eq (C) for methyl H atoms using a riding model. The methyl H atoms were allowed to rotate but not to tip.

Funding information
Funding for this research was provided by: Deutsche View of the hydrogen-bonded layers extending parallel to (101). Hydrogen bonds are shown as dashed lines.

Bis(acetonitrile-κN)bis(4-benzoylpyridine-κN)bis(thiocyanato-κN)cobalt(II)
Crystal data 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.