2,2′-[(1E,2E)-1,2-Bis(hydroxyimino)ethane-1,2-diyl]dipyridinium hexachloridorhenate(IV)

The title salt, (C12H12N4O2)[ReCl6], consists of 2,2′-[(1E,2E)-1,2-bis(hydroxyimino)ethane-1,2-diyl]dipyridinium cations and [ReCl6]2− anions which are both located on inversion centres. Each cation consists of a glyoxime moiety attached to two protonated pyridine rings in ortho positions. In the crystal, E,E isomers of the cation are observed which differ in the spatial arrangement of the pyridine rings. These rings are positionally disordered over two positions with site-occupancy factors of 0.786 (7) and 0.214 (7). The geometry of the cation is compared with that of a recently reported dipyridylglyoxime with the same configuration. The cations and anions are involved in a network of intermolecular O—H⋯Cl, N—H⋯Cl and C—H⋯Cl hydrogen bonds.

The title salt, (C 12 H 12 N 4 O 2 )[ReCl 6 ], consists of 2,2 0 -[(1E,2E)-1,2-bis(hydroxyimino)ethane-1,2-diyl]dipyridinium cations and [ReCl 6 ] 2À anions which are both located on inversion centres. Each cation consists of a glyoxime moiety attached to two protonated pyridine rings in ortho positions. In the crystal, E,E isomers of the cation are observed which differ in the spatial arrangement of the pyridine rings. These rings are positionally disordered over two positions with site-occupancy factors of 0.786 (7) and 0.214 (7). The geometry of the cation is compared with that of a recently reported dipyridylglyoxime with the same configuration. The cations and anions are involved in a network of intermolecular O-HÁ Á ÁCl, N-HÁ Á ÁCl and C-HÁ Á ÁCl hydrogen bonds.
In the crystal structure reported here both cation and anion are centrosymmetric. The cation is built up by the planar glyoxime fragment, HO-N=C-C=N-OH and two protonated pyridyl rings. The pyridyl groups are attached to the dioxime unit via C atoms located at the ortho positions with respect to the N atoms. The (C 12 H 12 N 4 O 2 ) 2+ unit may adopt many geometries because of the conformations of the glyoxime moiety (resulting in E,E, E,Z or Z,Z isomers) and spatial arrangement of pyridyl rings in relation to the HO-N=C-C=N-OH fragment. In the studied crystal structure the cations are the E,E isomers where the glyoxime moieties form interplanar angles of about 55° with planes of aromatic rings. Similar values of the geometrical parameters are observed compared to those published by Sabaté & Delalu (2012) ( Table 2) for (1E,2E)-2,2′-dipyridylglyoxime. However slight differences in overall geometries can be distinguished.
Contrary to the studied cation, in the dioxime structure published previously the planar HO-N=C-C=N-OH unit is perpendicular to the planes of aromatic rings. The results reported here for the rhenium salt reveal that the presence of H atoms bonded to N atoms in aromatic rings involved in N-H···Cl hydrogen bonds (Table 1) as well as the mutual arrangement of (C 12 H 12 N 4 O 2 ) 2+ and [ReCl 6 ] 2ions influence the overall geometry of the cation compared to dipyridylglyoxime.
As was mentioned before, the two pyridyl rings are bonded via C atoms in ortho positions to the planar glyoxime moiety (viz. to C1 atoms). The aromatic rings are disordered over two positions and turned to each other by an angle of about 180° (Fig. 1). The pyridyl rings of the major-occupancy form an interplanar angle of 55.4 (1)° with the glyoxime unit, while the aromatic rings of the minor-occupancy form an angle of 60.2 (3)°. The observed disorder can be interpreted as a solid solution of isomers of the cation due to the arrangement of pyridyl groups, where the glyoxime units have the same geometry. The disorder can be considered in three ways. In the first case the two centrosymmetric conformers can be in the crystal which occur in 78 and 22%. In the second one the three isomers can be observed: one supplementary materials sup-2 Acta Cryst. (2012). E68, m1174-m1175 centrosymmetric in 56% and two noncentrosymmetric both in 22%. In the third case the four conformers can be considered: two centrosymmetric and two noncentrosymmetric. In all the cases the preferred conformer is the centrosymmetric one for which the pyridyl rings form the interplanar angle of 55.4 (1)° with HO-N=C-C=N-OH entity.

Experimental
(1E,2E)-2,2′-dipyridylglyoxime, C 12 H 10 N 4 O 2 used for the synthesis was obtained according to the method reported by Richardson et al., (2002). The K 2 [ReCl 6 ] was obtained as published previously (Enk, 1931). The potassium hexachloridorhenate was mixed with C 12 H 10 N 4 O 2 and acetic acid (molar ratio 1:1:3, respectively) and refluxed in water for 3 h at about 100 °C. The mixture was allowed to evaporate in air to give brown plate crystals.

Refinement
The H atoms of the N-H and O-H groups were located in difference Fourier maps but were introduced in positions calculated from geometry, with N-H = 0.88 Å and U iso (H) = 1.2U eq (N) and O-H = 0.84 Å and U iso (H) = 1.5U eq (O). The disorder of the pyridyl rings was modelled over two positions, with occupancies of 0.786 (7) and 0.214 (7); the minoroccupancy component was refined isotropically. The disorder of the aromatic ring of the minor-occupancy components was modelled using AFIX 66. EADP constrains were used for three pairs of disordered atoms: C11 and C31; N12 and C36, C16 and N32. The H atoms of aromatic rings were treated as riding atoms in geometrically idealized positions, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). The highest residual electron density of 1.40 e Å -3 was located 0.80 Å from Re; the deepest hole of -1.02 e Å -3 was located 0.62 Å from Re.

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.  (5)  N1 0.0173 (7) 0.0194 (7) 0.0177 (7) −0.0074 (5) −0.0066 (5) 0.0018 (5)  C1 0.0135 (7) 0.0167 (7) 0.0148 (7) −0.0067 (6) −0.0033 (6) 0.0029 (6)