Bis(cyanato-κN)tetrakis(2,6-dimethylpyrazine-κN 4)nickel(II)

Reaction of nickel(II) chloride with sodium cyanate and 2,6-dimethylpyrazine leads to single crystals of the title compound, [Ni(NCO)2(C6H8N2)4]. The nickel(II) cation is located about a centre of inversion and is octahedrally coordinated by two cyanate anions and four 2,6-dimethylpyrazine ligands, forming discrete complexes.


Susanne Wöhlert, Inke Jess and Christian Näther Comment
Recently we have reported on the synthesis, structures and properties of new coordination polymers based on paramagnetic transition metals, small-sized anionic ligands such as thiocyanato and selenocyanato, and N-donor ligands.
In the course of these investigations we found that new coordination compounds with bridging anionic ligands can be prepared by thermal decomposition of suitable precursor compounds, in which the anionic ligands are only terminally coordinated (Wriedt et al., 2009 andBoeckmann &Näther, 2010). In further investigations we also have shown that even metal formate coordination compounds can be prepared by this method (Boeckmann, Wriedt & Näther, 2010). In our current investigations we tried to prepare similar compounds based on transition metal cyanates with 2,6-dimethylpyrazine as a neutral co-ligand. Therefore, we have reacted nickel(II) chloride with sodium cyanate and 2,6-dimethylpyrazine which resulted in the formation of crystals of the title compound that were identified by single crystal X-ray diffraction.
The asymmetric unit of the title compound consists of one nickel(II) cation, which is located on a centre of inversion, one cyanato anion and two 2,6-dimethylpyrazine ligands in general positions (Fig. 1). In the crystal structure each nickel(II) cation is coordinated by two terminal N-bonded cyanato anions and four 2,6-dimethylpyrazine ligands into discrete complexes, and the coordination polyhedra around the Ni cations corresponds to a slightly distorted octahedra.
The anionic ligands are trans to each other and because of sterical crowding the 2,6-dimethylpyrazine ligand is coordinated via the nitrogen atom that is not neighbouring the methyl groups. The Ni-N distances range from 2.0396 (19) Å to 2.1983 (15) Å with angles between 88.72 (6) ° and 180 ° ( Table 1). The shortest intermolecular distances between the nickel(II) cations is 8.4963 (3) Å.

Refinement
C-H H atoms were positioned with idealized geometry (methyl H atoms were allowed to rotate but not to tip) and were refined isotropically with U iso (H) = 1.2U eq (C) (1.5 for methyl H atoms) and C-H distances of 0.93 Å for aromatic and 0.96 Å for methyl H atoms using a riding model.

Figure 1
Crystal structure of the title compound with labeling and displacement ellipsoids drawn at the 50 % probability level.

Bis(cyanato-κN)tetrakis(2,6-dimethylpyrazine-κN 4 )nickel(II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.40 e Å −3 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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.