catena-Poly[[bis(pyridine-κN)nickel(II)]-di-μ-thiocyanato-κ2 N:S;κ2 S:N]

In the title compound, [Ni(NCS)2(C5H5N)2]n, the Ni2+ cation is coordinated by four thiocyanate anions (μ-1,3) and two pyridine ligands within a slightly distorted octahedral configuration. The Ni—N bond lengths to the pyridine rings are 2.1189 (17) and 2.1241 (17) Å, whereas those to the thiocyanate anions are 2.0299 (18) and 2.0359 Å. The Ni—S bond lengths are 2.5357 (6) and 2.5568 (6) Å. The Ni2+ cations are linked by N:S-bridging thiocyanate ligands into chains extending along [010]. The Ni⋯Ni distance within the chains is 5.5820 (5) Å. The asymmetric unit contains two Ni2+ cations of which one is located on a centre of inversion, whereas the second is located on a general position.

In the title compound, [Ni(NCS) 2 (C 5 H 5 N) 2 ] n , the Ni 2+ cation is coordinated by four thiocyanate anions (-1,3) and two pyridine ligands within a slightly distorted octahedral configuration. The Ni-N bond lengths to the pyridine rings are 2.1189 (17) and 2.1241 (17) Å , whereas those to the thiocyanate anions are 2.0299 (18) and 2.0359 Å . The Ni-S bond lengths are 2.5357 (6) and 2.5568 (6) Å . The Ni 2+ cations are linked by N:S-bridging thiocyanate ligands into chains extending along [010]. The NiÁ Á ÁNi distance within the chains is 5.5820 (5) Å . The asymmetric unit contains two Ni 2+ cations of which one is located on a centre of inversion, whereas the second is located on a general position.

Comment
Recently, we reported on the synthesis, crystal structures and the magnetic properties of coordination polymers of composition [M(NCS) 2 (pyridine) 2 ] n with M = Mn, Fe, Ni, Co (Boeckmann & Näther, 2010, 2012. The Mn compound is an antiferromagnet, the Fe and Ni compounds show a metamagnetic transition whereas the Co compound shows a slow relaxation of the magnetization. The crystal structures of the compounds with Mn, Fe and Co were determined by single crystal x-ray diffraction, whereas for [Ni(NCS) 2 (pyridine) 2 ] n no single crystals were available at that time. However, the structure of the Ni compound was already reported by Reller & Oswald (1986). They found a monoclinic unit cell in which the pyridine rings are completely disordered. Weissenberg photographs gave hint for super structure reflections leading to a triclinic unit cell that is similar to that of the title compound. However, in that paper the monoclinic average structure was presented. Later we re-investigated the Ni compound in a different context and we accidentally obtained crystals suitable for single crystal x-ray analysis. Therefore, we have determined this structure in the correct unit cell. The isotypic structure of [Cu(NCS) 2 (pyridine) 2 ] n was already reported by Chen et al. (2005).
The asymetric unit of the title compound, [Ni(NCS) 2 (pyridine) 2 ] n , contains two crystallographically independent Nickel(II)-cations, of which one (Ni2) is located on general position whereas the second one (Ni1) is located on a crystallographic inversion centre. In the crystal structure each Ni(II) cation is octahedrally coordinated by two N-and two S-atoms from the thiocyanato anions and by two N-atoms from the pyridine ligands. The Ni cations are linked by N,S bridging thiocyanato anions into chains that are elongated along the crystallographic b-axis (Fig. 2).

Experimental
NiSO 4 .6H 2 O was obtained from Merck, Pyridine was obtained from Riedel-de Haen and Ba(NCS) 2 was obtained from Alfa Aesar. Ni(NCS) 2 was prepared by stirring Ba(NCS) 2 *3H 2 O (17.5 g, 56.9 mmol) and NiSO 4 *6 H 2 O (15.0 g, 57 mmol) in water (500 mL) for two hours. The white residue of BaSO 4 was filtered off and the solution was evaporated using a rotary evaporator. The homogeneity of the product was investigated by X-ray powder diffraction and elemental analysis.
The title compound was prepared by the reaction of 9.1 mg Ni(NCS) 2 (0.05 mmol) and 2.02 µL Pyridin (0.025 mmol) in 2.0 mL EtOH which was overlayed by 2.0 mL Hexan in a sealed 10 mL glass-vessel at 75°C. After 2 days the solution was slowly cooled down and green blocks of the title compund start to grow.

Refinement
All H atoms were located in difference map but were positioned with idealized geometry and were refined isotropic with U iso (H) = 1.2 U eq (C) of the parent atom using a riding model with C-H = 0.93 Å.  Molecular structure of the title compound. Anisotropic displacement ellipsoids drawn at the 50% probability level.  Crystal structure of the title compound viewed along the crystallographic b-axis.

catena-Poly[[bis(pyridine-κN)nickel(II)]-di-µ-thiocyanato-κ 2 N:S;κ 2 S:N]
Crystal data [Ni(NCS) 2 (C 5 H 5 N) 2 ] M r = 333.07 Triclinic, P1 a = 8.4913 (5) Å b = 8.6808 (5) Å c = 15.3608 (9) Å α = 92.675 (5) where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.59 e Å −3 Δρ min = −0.61 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq