4,4′-Di-tert-butyl-2,2′-dipyridinium dichloride

In the title compound, C18H26N2 2+·2Cl−, the complete dication is generated by crystallographic inversion symmetry; both N atoms are protonated and engaged in strong and highly directional N—H⋯Cl hydrogen bonds. Additional weak C—H⋯Cl contacts promote the formation of a tape along ca. [110]. The crystal structure can be described by the parallel packing of these tapes. The crystal studied was a non-merohedral twin with twin law [−1 0 0, 0 −1 0, −0.887 0.179 1] and the final BASF parameter refining to 0.026 (2) .


D-HÁ
Data collection: APEX2 (Bruker, 2006); cell refinement: SAINT-Plus (Bruker, 2005); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2009); software used to prepare material for publication: SHELXTL.   (Allen, 2002) reveals that this molecule forms relatively stable complexes with a large range of metallic cations, including lanthanides, actinides and, mainly, d-block cations. Surprisingly, not many crystallographic reports are known in which 4,4'-di-tert-butyl-2,2'-dipyridyl is chelated to either s-or p-block cations: there is a single report in the literature of an organometallic complex with Na + by Li et al. (2005), and another very recent with Sn 4+ by Momeni et al. (2010). Concerning organic crystals, besides the crystal structure of 4,4'-di-tert-butyl-2,2'-dipyridyl which was recently reported by our group (Amarante & Figueiredo et al., 2009), there is a single crystallographic determination in which this molecule co-crystallizes with hexafluorobenzene (Batsanov et al., 2007). As a continuation of our on-going interest in organic crystals based on pyridine derivatives Coelho et al., 2007;Paz & Klinowski, 2003;Paz et al., 2002), here we wish to report the crystal structure of the title compound (I) at 150 K, which is an organic salt with chloride anions. Noteworthy, a search in the literature reveals the existence of only one other salt of protonated 4,4'-di-tert-butyl-2,2'-dipyridyl moieties, being reported by Herrmann et al. (1990) and using perrhenate as the charge-balancing anion.
The asymmetric unit of the title compound is composed of half of a 4,4'-di-tert-butyl-2,2'-dipyridinium cation (the molecule has its geometrical centre located over an inversion center) and by a single chloride anion strongly hydrogen bonded to the neighbouring N + -H group as depicted in Figure 1. As a consequence, the 4,4'-di-tert-butyl-2,2'-dipyridinium cation adopts a typical trans conformation around the central C-C bond, very much similar to that observed by us in the crystal structure of the molecule itself (Amarante & Figueiredo et al., 2009) and also by Batsanov et al. (2007) in the co-crystal with hexafluorobenzene. This conformation permits a significant reduction of the overall steric repulsion due to the large tert-butyl substituent groups.
Each diprotonated organic cation is engaged in a strong and highly directional N + -H···Clhydrogen bonding interaction with the charge-balancing anions (Table 1 and Figures 1 and 2). These intermolecular connections are further strengthened by the presence of a number of weak C-H···Cl contacts as depicted in Figure 2 (see geometrical details in Table 2), leading to the formation of a supramolecular hydrogen-bonded tape composed of alternating R 1 2 (7) and R 2 4 (10) graph set motifs (Grell et al., 1999). The crystal structure of the title compound is obtained by the close packing of these supramolecular tapes as shown in Figure 3. supplementary materials sup-2 Experimental Irregular, poorly-formed crystals of the title compound were isolated as a minor secondary product during the preparation of the oxodiperoxo complex MoO(O 2 ) 2 (tbbpy) (where tbbpy stands for 4,4'-di-tert-butyl-2,2'-dipyridyl) previously reported by our group .

Refinement
Hydrogen atoms bound to carbon have been placed at their idealized positions and were included in the final structural model in riding-motion approximation with C-H distances of 0.95 Å (aromatic C-H) and 0.98 Å (terminal -CH 3 groups). The hydrogen atom bound to the nitrogen atom was directly located from difference Fourier maps and was included in the final structural model with the N-H distance restrained to 0.95 Å. The isotropic displacement parameters for these hydrogen atoms were fixed at 1.2 (for the former family of hydrogen atoms) or 1.5×U eq (for the two latter families) of the respective parent atoms.
The final structural refinement was performed by using the twin law [-1 0 0, 0 -1 0, -0.887 0.179 1] (Cooper et al., 2002) with the final BASF parameter refining to 0.026 (2). Fig. 1. Schematic representation of the molecular units composing the crystal structure of the title compound. Non-hydrogen atoms are represented as displacement ellipsoids drawn at the 70% probability level. Hydrogen atoms are depicted as small spheres with arbitrary radii. The atomic labeling for all non-hydrogen atoms composing the asymmetric unit is provided.  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.