Crystal structure of bis(isonicotinamide-κN 1)bis(thiocyanato-κN)zinc

The crystal structure consists of discrete tetrahedral complexes, that are linked by intermolecular N—H⋯O, C—H⋯O and N—H⋯O hydrogen bonding.


Chemical context
The synthesis of magnetic materials is still a major field in coordination chemistry (Liu et al., 2006). For their construction, paramagnetic cations can be linked by small anionic ligands such as thiocyanate anions to enable a magnetic exchange between the cations (Palion-Gazda et al., 2015;Banerjee et al., 2005). In this context we have reported on a number of coordination polymers with thiocyanato ligands that show different magnetic phenomena, including a slow relaxation of the magnetization which is indicative of singlechain magnetism (Werner et al., 2014;2015a,b,c). In several cases, such phases can only be prepared by thermal decomposition of suitable precursor compounds , leading to microcrystalline powders for which a straightforward crystal structure determination is difficult. In order to avoid this scenario, compounds of the same composition based on cadmium or zinc can be prepared in the form of single crystals. In many cases, such zinc and cadmium compounds are isotypic to the paramagnetic analogues, and the structure of the latter can then easily be refined by the Rietveld method . It should be mentioned that the structures of cadmium compounds are useful as prototypes for transition metal compounds with octahedral coordination spheres, whereas the structures of zinc compounds are useful prototypes for compounds with tetrahedral coordination spheres for the transition metal. The thermal decomposition of cobalt complexes is an example of the latter. In the course of our systematic investigation in this regard, we became interested in isonicotinamide as a co-ligand to be reacted with Zn(SCN) 2 . The synthesis and crystal structure of the resulting compound, [Zn(NCS) 2 (C 6 H 6 N 2 O) 2 ], are reported here.

Structural commentary
The asymmetric unit of the title compound consists of one Zn 2+ cation, one thiocyanate anion and one neutral isonicotinamide ligand. The thiocyanate anion and the isonicotinamide ligand are located on general positions whereas the Zn 2+ cation is located on a twofold rotation axis. The Zn 2+ cation is tetrahedrally coordinated by two terminal N-bonded thiocyanato ligands and by two isonicotinamide ligands through their pyridine N atoms into a discrete complex (Fig. 1). As expected, the Zn-N bond length involving the thiocyanate anion (N1) is significantly shorter than that to the pyridine N atom (N11) of the neutral ligand ( Table 1). The angular distortion of the ZnN 4 tetrahedron is noticeable, with N-Zn-N angles ranging from 104.32 (13) to 123.6 (2) .

Supramolecular features
In the crystal structure, the discrete complexes are stacked along the c axis and are linked by intermolecular N-HÁ Á ÁO hydrogen bonding between one of the two amide H atoms and the amide O atom of a neighboring complex ( Fig. 2 and Table 2). There is a further weak contact between one aromatic H atom of the pyridine ring and the carbonyl O atom of a neighboring complex ( Table 2). The second H atom of the NH 2 group is involved in intermolecular N-HÁ Á ÁS hydrogen bonding to the S atoms of the anionic ligand. In this way a three-dimensional hydrogen-bonded network is formed.

Figure 1
View of the discrete complex with labelling and displacement ellipsoids drawn at the 50% probability level. [Symmetry code: (i) Àx + 1, Ày + 1, z.] ZnSO 4 ÁH 2 O (10 mmol) in 350 ml water. The white residue was filtered off and the filtrate was dried using a rotary evaporator. The homogenity was checked by X-ray powder diffraction and elemental analysis. Crystals of the title compound suitable for single crystal X-Ray diffraction were obtained by the reaction of 27.2 mg Zn(NCS) 2 (0.15 mmol) with 36.64 mg isonicotinamide (0.3 mmol) in methylcyanide (1.5 ml) within a few days.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. C-and N-bound H atoms were located in a difference Fourier map but were positioned with idealized geometry. They were refined with U iso (H) = 1.2U eq (C, N) using a riding model with C-H = 0.95 Å for aromatic and N-H = 0.88 Å for the amide H atoms. The absolute structure was determined and is in agreement with the selected setting [Flack x parameter: 0.005 (19) by classical fit to all intensities (Flack, 1983) and À0.005 (8)  The packing of the complexes in the title compound, in a view along the c axis. Intermolecular hydrogen bonding is shown as dashed lines. Computer programs: X-AREA (Stoe, 2008), SHELXS97 and XP in SHELXTL (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015), DIAMOND (Brandenburg, 1999) and publCIF (Westrip, 2010).

Bis(isonicotinamide-κN 1 )bis(thiocyanato-κN)zinc
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.