Hexakis(1H-imidazole-κN 3)cobalt(III) tris(hexafluoridophosphate) hexahydrate

In the crystal structure of the title compound, [Co(C3H4N2)6](PF6)3·6H2O, the CoIII atom lies on a special position with site-symmetry and the P atom is located on a special position with site symmetry . The CoIII atom has an almost ideal octahedral coordination formed by the N atoms of six imidazole ligands. The water molecules form hydrogen-bonded helical chains propagating in [001] by O—H⋯O interactions with a distance of 2.913 (2) Å. They simultaneously interact as hydrogen-bond acceptors and donors with the cations and anions, respectively, resulting in the formation of a three-dimensional assembly. Weak C—H⋯F interactions further stabilize the crystal structure.

In the crystal structure of the title compound, [Co(C 3 H 4 N 2 ) 6 ]-(PF 6 ) 3 Á6H 2 O, the Co III atom lies on a special position with sitesymmetry 3 and the P atom is located on a special position with site symmetry 1. The Co III atom has an almost ideal octahedral coordination formed by the N atoms of six imidazole ligands. The water molecules form hydrogenbonded helical chains propagating in [001] by O-HÁ Á ÁO interactions with a distance of 2.913 (2) Å . They simultaneously interact as hydrogen-bond acceptors and donors with the cations and anions, respectively, resulting in the formation of a three-dimensional assembly. Weak C-HÁ Á ÁF interactions further stabilize the crystal structure.

S1. Comment
During the course of ongoing studies on Co III complexes with heterocycles (Wojtczak et al., 1990;Pazderski et al., 2008) the title compound (I) was isolated. The crystal structure of (I) is built of mononuclear [Co(imidazole) 6 ] 3+ trications with the Co1 atom lying on Wyckoff position 3a (site symmetry 3), PF 6anions with P atom lying on Wyckoff position 9 d (site symmetry 1) and lattice water molecules ( Fig.1). It is worth mentioning that this is the first structure consisting of a hexakis(imidazole)-cobalt(III) cationic complex, whereas more than 15 structures consisting of a hexakis(imidazole)cobalt(II) complex ion were reported. Furthermore, there are only two papers on the hexakis(imidazole)-cobalt(III) ion in solution, describing spectroscopic (Navon & Panigel, 1989) and kinetic properties (Wiśniewska & Kita, 2006) respectively. The Co III ion has an almost ideal octahedral environment formed by six imidazole N atoms, with cis-N-Co -N angles of 88.68 (7)° and 91.32 (7)°. The planes of neighbouring imidazole rings are twisted from their usual perpendicular positions. This is the result of the extensive net of hydrogen bonds in the structure in which imidazole rings are involved (dihedral angle = 72.4 (6)°). The Co-N bond distance is equal to 1.961 (1) Å and as expected is slightly shorter than those reported for hexakis(imidazole)-cobalt(II) complexes with distances of 2.140±2.188 Å (Tong et al., 2002). A similar relation of bond lengths was reported for Co III -N and Co(II)-N in hexaamminecobalt complexes (Kime & Ibers, 1969) with differences between those distances of 0.18 Å. The water molecules present in the crystal structure form helical chains (helix pitch = 7.016 (2) Å, c axis) similar to those observed in a trichlorophloroglucinol structure (Saha & Nangia, 2005). They are propagated in [001] directions by O1-H6···O1 i interactions (symmetry operation: -y + 2/3, x-y + 1/3, z + 1/3) with a distance of 2.913 (2) Å), which are stabilized by hydrogen bonding with the remaining molecular units (Table 1) giving in turn a three-dimensional assembly. The weak C-H···F interactions (Table   1) further stabilize the packing arrangement (Fig. 2).

S2. Experimental
A mixture of 11.84 g (174 mmol) of imidazole and 2.02 g (5 mmol) of Co(pyridine) 3 Cl 3 was grinded for several minutes until the color changed from green to red. The mixture was subsequently dissolved in 100 ml of distilled water and the pH was adjusted to 2-3 by adding 3 M HCl. Then the mixture was diluted with water to a final volume of 2 l and passed through a Sephadex SP C-25 column starting with an aqueous 0.05 M HCl solution as eluent. The fraction obtained by using 0.2 M HCl was evaporated in a stream of cold air and the product [Co(imidazole) 6 ]Cl 3 was filtrated and washed with ethanol. 10 mg of this compound was placed in a 50 ml beaker and 20 ml of a saturated aqueous solution of NH 4 PF 6 was added. Red crystals suitable for single-crystal X-ray analysis were obtained by slow evaporation.

S3. Refinement
Water H atoms were located in a difference map and refined with a restrained O-H distance of 0.96 (3) Å, whereas U iso (H) values were allowed to refine independently. The remaining H atoms were positioned geometrically, with C-H = supporting information sup-2 Acta Cryst. (2009). E65, m1256-m1257 0.95 Å and N-H = 0.88 Å, and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C,N).

Figure 1
The molecular structure of (I), with the atom-numbering scheme [symmetry codes:(i) y,-x + y,-z; (ii) -x + y, -x, z; (iii) -x,y, -z; (iv) -y, x-y, z; (v) x-y, x, -z; (vi) -x + 2/3,-y + 1/3,-z + 1/3]. Displacement ellipsoids are drawn at the 50% probability level.  The crystal packing of (I) viewed down [001] with the extensive net of hydrogen bonds leading to a three-dimensional arrangement (the red dashed lines indicate strong hydrogen bonding and the blue weak ones). Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.0444P) 2 + 4.9022P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.54 e Å −3 Δρ min = −0.31 e Å −3 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.

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