Tris(propane-1,2-diamine-κ2 N,N′)nickel(II) tetracyanidonickelate(II)

The title compound, [Ni(C3H10N2)3][Ni(CN)4], is built up of [Ni(pn)3]2+ cations (pn is 1,2-diaminopropane) and [Ni(CN)4]2− anions. Both NiII atoms in the cation and the anion lie on a mirror plane. The respective ions interact through Coulombic forces and through a complex network of hydrogen bonds. Extended disorder associated with the cation has been resolved. The occupancies of the respective disordered positions are 0.4:0.4:0.2.

The title compound, [Ni(C 3
The Pt analogue was described by Potočňák et al. (2008).
The Ni II atom in the complex cation exhibits pseudo-octahedral coordination by six nitrogen atoms from three chelate bonded pn ligands in gauche conformations. As the nickel atom occupies the position on a mirror plane the chelate bonded ligands are disordered in two positions with half occupancy (Fig. 1). Further disorder associated with the position of the methyl groups bonded to the carbon atom was detected so within the same metallocycle both R and S enantiomers are present with the same occupancy. Moreover, the structure is centrosymmetric so both opposite absolute configurations Λδδλ and Δλλδ of the chiral cations are present in the unit cell in equal quantities. It is worth noting that for the synthesis a racemic mixture of the pn ligand was used. The observed geometrical parameters are close to those observed in [Saha et al., 2005].
The charge of the cation is compensated by a [Ni(CN) 4 ] 2anion. The latter is bisected by a mirror plane, leading to a rather regular NiC 4 chromophore. The geometric characteristics are similar to those previously reported [Smékal et al., 2001].
The Ni II atoms in the respective ions are not connected by covalent bonds, the shortest distance between Ni II atoms being 8.527 (1) Å. The cations are connected by a complicated system of weak intermolecular hydrogen bonds of the N-H···N≡C-Ni-C≡N···H-N type, in which also the complex anions take part and where the H···N distance range is 2.103-2.488 Å.

Experimental
To 10  suitable for X-ray studies, appeared after one day.

Refinement
The structure was solved by direct method. The model (including two 50:50% disordered positions of the pn ligands, forced by the crystallographic mirror symmetry in the cation) was completed by subsequent Fourier syntheses. At this stage the supplementary materials sup-2 calculated difference Fourier map indicated the presence of further positional disorder of the methyl groups in the pn ligands. The occupational factors refined by fixing the common isotropic thermal parameters of the concerning carbon atoms indicated 50:50 occupancy which was in the subsequent refinement cycles fixed. Finally, the hydrogen atoms were put in the calculated positions taking into account the observed disorder. Anisotropic thermal parameters were refined for all non-H atoms. All H atoms positions were calculated using the appropriate riding model with isotropic temperature factors being 1.2 times larger then temperature factors of their parent atoms. Geometrical analysis was performed using PARST (Nardelli, 1983) and SHELXL97. 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 Rfactors(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.