Crystal structure of diaquabis(2-chloropyridine-κN)bis(thiocyanato-κN)nickel(II)

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


Chemical context
The synthesis of materials with interesting cooperative magnetic properties is still a major field in coordination chemistry (Zhang et al., 2011). One feasible strategy for the preparation of such compounds is to link paramagnetic cations with small anionic ligands such as, for example, thiocyanate anions to enable a magnetic exchange between the cations (Palion-Gazda et al., 2015;Massoud et al., 2013). In this regard, our group has reported on a number of coordination polymers with bridging thiocyanato ligands. Dependent on the metal cation and the neutral co-ligand, they show different magnetic phenomena including a slow relaxation of the magnetization, which is indicative for single-chain magnetism (Werner et al., 2014(Werner et al., , 2015a. In the context of this research, discrete complexes are likewise of interest because such compounds can be transformed into the desired polymeric systems by thermal decomposition . In view of our systematic studies, we became interested into compounds based on 2-chloropyridine as co-ligand, for which only two different polymorphs were found for representatives containing Zn or Co . In a more recent study, investigations were also carried out for Ni that led to the title compound being characterized by single crystal X-ray diffraction. Unfortunately, no single-phase crystalline powder could be synthesized, which prevented further investigations of its physical properties.

Structural commentary
The asymmetric unit of the title compound, [Ni(NCS) 2 (C 5 H 4 NCl) 2 (H 2 O) 2 ], consists of one Ni II cation, one thiocyanate anion, one water molecule and one neutral 2-chloropyridine co-ligand. The cation is located on a center of inversion whereas all ligands are located on general positions.
The Ni II cation is coordinated by two terminal N-bound inorganic anionic ligands, two water molecules and two 2-chloropyridine ligands that are coordinated via the pyridine N atom in an all-trans configuration (Fig. 1). As expected, and in agreement with values reported in literature (Ðaković et al., 2008;Werner et al., 2015b), the Ni-N bond lengths to the thiocyanato ligands are significantly shorter[2.018 (3) Å ] than to the pyridine N atom of the neutral 2-chloropyridine ligand [2.208 (3) Å ].

Supramolecular features
In the crystal, discrete complexes are linked by pairs of intermolecular O-HÁ Á ÁS hydrogen bonds between one of the two water H atoms and the thiocyanato S atoms of a neighboring complex into centrosymmetric dimers that are further connected into chains along the b axis (Fig. 2, Table 1). Neighbouring complexes are additionally linked in the same direction by pairs of C-HÁ Á ÁCl hydrogen bonds between the chloro substituent of one complex and one pyridine H atom of a neighbouring complex (Fig. 2, Table 1). These chains are further linked by O-HÁ Á ÁS hydrogen bonding between the second water H atom of one complex and a thiocyanato S atom of a neighbouring complex into layers parallel to the bc plane ( Fig. 3

Database survey
To the best of our knowledge, there are only four coordination compounds containing thiocyanato and 2-chloropyridine ligands deposited in the Cambridge Structure Database (Version 5.37, last update 2015; Groom et al., 2016). The structures consist of tetrahedrally coordinated metal cations (Co and Zn) where each metal cation is surrounded by two 2-chloropyridine ligands as well as two thiocyanate anions . A general search for coordination compounds with 2-chloropyridine ligands resulted in 16 structures including the aforementioned ones. Two examples relate to a Pd compound, similar to the Co and Zn ones, however with the Pd II cation in a square-planar conformation coordinated by two 2-chloropyridine ligands as well as two azide anions (Beck et al., 2001) as well as a Cu compound with a square-pyramidal coordinated metal cation surrounded by two 2-chloropyridine ligands, one water ligand and two chloride anions (Jin et al., 2005). View of a discrete complex with labelling and displacement ellipsoids drawn at the 50% probability level. [Symmetry code: (i) Àx + 1 2 , Ày + 3 2 ,z.+1.]

Diaquabis(2-chloropyridine-κN)bis(thiocyanato-κN)nickel(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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )