Diaquabis(nicotinamide-κN 1)bis(thiocyanato-κN)nickel(II)

In the title complex, [Ni(NCS)2(C6H6N2O)2(H2O)2], the NiII ion is located on an inversion center and is coordinated in a distorted octahedral environment by two N atoms from two nicotinamide ligands and two water molecules in the equatorial plane, and two N atoms from two thiocyanate anions in the axial positions, all acting as monodentate ligands. In the crystal, weak N—H⋯S hydrogen bonds between the amino groups and the thiocyanate anions form an R 4 2(8) motif. The complex molecules are linked by O—H⋯O, O—H⋯S, and N—H⋯S hydrogen bonds into a three-dimensional supramolecular structure. Weak π–π interactions between the pyridine rings is also found [centroid–centroid distance = 3.8578 (14) Å].

In the title complex, [Ni(NCS) 2 (C 6 H 6 N 2 O) 2 (H 2 O) 2 ], the Ni II ion is located on an inversion center and is coordinated in a distorted octahedral environment by two N atoms from two nicotinamide ligands and two water molecules in the equatorial plane, and two N atoms from two thiocyanate anions in the axial positions, all acting as monodentate ligands. In the crystal, weak N-HÁ Á ÁS hydrogen bonds between the amino groups and the thiocyanate anions form an R 4 2 (8) motif. The complex molecules are linked by O-HÁ Á ÁO, O-HÁ Á ÁS, and N-HÁ Á ÁS hydrogen bonds into a three-dimensional supramolecular structure. Weakinteractions between the pyridine rings is also found [centroid-centroid distance = 3.8578 (14) Å ].

Related literature
For background to the applications of transition metal complexes with biochemically active ligands, see: Antolini et al. (1982); Krishnamachari (1974).

Comment
Transition metal complexes with biochemically active ligands frequently show interesting physical and/or chemical properties, as a result they may find applications in biological systems (Antolini et al., 1982). As ligands, nicotinamide (NA) and thiocyanate are interesting due to their potential formation of metal coordination complexes as they exhibit multifunctional coordination modes due to the presence of S and N donor atoms. With reference to the hard and soft acids and bases concept, the soft cations show a pronounced affinity for coordination with the softer ligands, while hard cations prefer coordination with harder ligands (Hökelek, Dal et al., 2009;Hökelek, Yilmaz et al., 2009;Özbek et al., 2009;Zhu et al., 2006). NA is one form of niacin and a deficiency of this vitamin leads to loss of copper from body, known as pellagra disease. The nicotinic acid derivative N,N-diethylnicotinamide (DENA) is an important respiratory stimulant.
In the title complex, the Ni II ion is located on an inversion center and coordinated by two equatorial N atoms from two NA ligands and two equatorial O atoms from water molecules, and two axial N donor from thiocyanate ligands, as can be seen in Fig. 1. The Ni-O1W bond distance is 2.088 (2) Å, which is very close to the Ni-N3(thiocyanate) distance of 2.090 (2)  As can be seen from the packing diagram (Fig. 2), the complex molecules are linked by intermolecular O-H···O, O-H···S and N-H···S hydrogen bonds (Table 1), forming a supramolecular structure. The discrete molecules are connected by O1W-H···O1 and O1W-H···S1 hydrogen bonds into a two-dimensional layer parallel to (010). The thiocyanate S1 atom also accepts the other two hydrogen bonds from two different amide N atoms, completing an overall threedimensional supramolecular structure.
Greenish blue colour solution was obtained. After filtration the final clear solution left undisturbed at room temperature for slow evaporation. Next day, needle shaped greenish blue crystals were collected and dried in vacuo over silica gel.
Crystals suitable for single crystal X-ray diffraction were manually selected and immersed in silicon oil. map and refined isotropically.

Figure 2
Packing diagram of the title complex. Hydrogen bonds are shown as dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.