A compressed octahedral cobalt(II) complex in the crystal structure of diaqua[6,6′-sulfanediylbis(2,2′-bipyridine)]cobalt(II) dinitrate

The [Co(C20H14N4S)(H2O)2]2+ cation in the title compound possesses pseudo-C 2v point-group symmetry.


Chemical context
The control of the molecular structure of coordination compounds is an important task in crystal engineering. It is well known that organic ligands play a significant role in determining the crystal structure of coordination complexes. For example, bidentate 2,2 0 -bipyridine or its derivatives are common ligands that can be employed to assemble functional compounds (Zhang et al., 2014;Kamdar et al., 2016;Pal et al., 2014). Linking two 2,2 0 -bipyridine units through a suitable atom leads to a tetradentate ligand (Knight et al., 2010) and, more importantly, the distance of the two 2,2 0 -bipyridine moieties can then be controlled by the type and size of the bridging atom. As a consequence, the coordination geometry of the metal cation can be affected.

Structural commentary
The asymmetric unit of the title salt ( Fig. 1) (Li et al., 2016;Knight et al., 2010;Suckert et al., 2017;Zhong et al., 2008;Hathwar et al., 2017). The O-Co-O angle is almost linear at 178.59 (7) . The four equatorial N atoms and the Co II cation are approximately coplanar, with the largest deviation from the least-squares plane being 0.039 Å for N3.
In a similar Co II complex with the 6,6 0 -sulfanediylbis(2,2 0bipyridine) ligand replaced by the tetradentate ligand bis(2,2 0bipyrid-6 0 -yl)ketone (Knight et al., 2010), the Co II cation is slightly convex (0.098 Å ) from the plane formed through four coordination N atoms. The Co-O bond lengths of the two axial sites are significantly different at 2.075 (4) Å for that in the convex site and 2.118 (4) Å for that in the concave site. The corresponding O-Co-O bond angle deviates more distinctly from linearity with a value of 172.46 (17) . The structural differences between the title complex and the similar reported compound are ascribed to the bridging atom between the two 2,2 0 -bipyridine moieties, i.e. an S atom in the title complex versus a C atom of a keto group in the related compound. The bridging bonds [C-S: 1.761 (2) and 1.764 (2) Å ] of the title complex are longer than those [C-C: 1.496 (10) and 1.500 (10) Å ] in the related complex.

Supramolecular features
The coordinating water molecules act as proton donors, forming O-HÁ Á ÁO hydrogen bonds with the NO 3 À anions and leading to an extended layer structure parallel to (001) for the title complex (Fig. 2). For these hydrogen bonds, the OÁ Á ÁO distances are in the range of 2.688 (2)-2.789 (2) Å , indicating they are of medium strength (Table 1), and are comparable with other hydrogen bonds formed between coordinating water molecules and NO 3 À anions (Kurdziel et al., 2000;Kunz et al., 2007;Wang et al., 2012). There are no intermolecular interactions in the molecular packing of the title complex.

Figure 1
The structures of the molecular entities in the structure of the title salt. Displacement ellipsoids are drawn at the 50% probability level. diylbis(2,2 0 -bipyridine) (34.4 mg, 0.1 mmol), which afforded a light-yellow solution, which was stored at ambient conditions. Yellow crystals of the title compound were obtained by slow evaporation of the solvent, yield: ca. 50%.

Diaqua[6,6′-sulfanediylbis(2,2′-bipyridine)]cobalt(II) dinitrate
Crystal data [Co(C 20  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.