Bis(dicyanamido-κN)tetrakis(pyridine-κN)nickel(II)

In the crystal structure of the title compound, [Ni(C2N3)2(C5H5N)4], the NiII cations are coordinated by four pyridine ligands and two dicyanamide anions into discrete complexes. The shortest Ni⋯Ni separation is 8.1068 (10) Å. The structure is pseudo-centrosymmetric and can also be refined in the space group C2/c in which both anionic ligands are strongly disordered and the refinement leads to significantly poorer reliability factors.

In the crystal structure of the title compound, [Ni(C 2 N 3 ) 2 -(C 5 H 5 N) 4 ], the Ni II cations are coordinated by four pyridine ligands and two dicyanamide anions into discrete complexes. The shortest NiÁ Á ÁNi separation is 8.1068 (10) Å . The structure is pseudo-centrosymmetric and can also be refined in the space group C2/c in which both anionic ligands are strongly disordered and the refinement leads to significantly poorer reliability factors.

Experimental
Crystal data [Ni(C 2  Data collection: X-AREA (Stoe & Cie, 2008); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2011); software used to prepare material for publication: XCIF in SHELXTL. (Boeckmann & Näther;2010;Boeckmann & Näther, 2011). The bridging compounds with e.g. pyridine can be prepared by thermal decomposition of discrete complexes with terminal bonded anionic ligands. In the course of systematic investigations we also started to investigated similar compounds based on dicyanamide (Wriedt & Näther, 2011). Within this project crystals of the title compound were obtained, which were characterized by single-crystal X-ray diffraction. In the crystal structure of the title compound each nickel(II) cation is six-coordinated by two dicyanamido anions and four pyridine ligands in a slightly distorted octehedral geometry (Fig. 1). The NiN 6 distances ranges from 2.057 (3) Å to 2.169 (3) Å and the angles are between 86.59 (11) ° and 178.96 (15)°. In the crystal structure, the discrete complexes are connected through intermolecular N-HC hydrogen bonds with an N···H distances of 2.559 Å (Fig. 2). The shortest nickel(II)-nickel(II) distance between the complexes is 9.157 Å.
It must be noted that a discrete nickel(II) dicyanamide complex is reported (Wu et al., 2004) with 1,10-phenanthroline as co-ligands in which all ligands are cis-coordinated.

Refinement
All H atoms were located in difference map but were positioned with idealized geometry and were refined isotropic with U eq (H) = 1.2 U eq (C) of the parent atom using a riding model with C-H = 0.95 Å. The structure is pseudocentrosymmetric and can also be refined in the centrosymmetric space group C2/c. However, in C2/c the complexes are located on centres of inversion and the anionic ligands are strongly disorderd which is not the case in space group Cc.
Moreover, in C2/c the reliability factors are very poor and no reasonable structure model can be found. Therefore, Cc was selected, in which the structure can be very easily refined. In this case the absolute structure cannot be determined presumable, because of the pseudo-symmetry and therefore, a twin refinement for racemic twinning was performed leading to an BASF parameter of 0.53 (2). SHELXL97 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2011); software used to prepare material for publication: XCIF in SHELXTL (Sheldrick, 2008).

Figure 1
The molecular structure of the title compound with labelling and displacement ellipsoids drawn at the 50% probability level.  Crystal structure of the title compound with a view of the discrete complexes (green = nickel(II), blue = nitrogen, grey = carbon and white = hydrogen).

Bis(dicyanamido-κN)tetrakis(pyridine-κN)nickel(II)
Crystal data Hall symbol: C -2yc a = 13.0439 (6) (6) 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.