Tris(cis-2-hydroxycyclohexane-1,3,5-triaminium) hydrogen sulfate octachloride dihydrate

The 2-hydroxycyclohexane-1,3,5-triaminium (= H3 L 3+) cation of the title compound, 3C6H18N3O3+·8Cl−·HSO4 −·2H2O, exhibits a cyclohexane chair with three equatorial ammonium groups and one axial hydroxy group in an all-cis configuration. The hydrogen sulfate anion and two water molecules lie on or in proximity to a threefold axis and are disordered. The crystal structure features N—H⋯Cl and O—H⋯Cl hydrogen bonds. Three C 3-symmetric motifs can be identified in the structure: (i) Two chloride ions (on the C 3-axis) together with three H3 L 3+ cations constitute an [(H3 L)3Cl2]7+ cage. (ii) The lipophilic C6H6-sides of three H3 L 3+ cations, which are oriented directly towards the C 3-axis, generate a lipophilic void. The void is filled with the disordered water molecules and with the disordered part of the hydrogen sulfate ion. The hydrogen atoms of these disordered moieties were not located. (iii) Three H3 L 3+ cations together with one HSO4 − and three Cl− counter-ions form an [(HSO4)(H3 L)3Cl3]5+ cage. Looking along the C 3-axis, these three motifs are arranged in the order (cage 1)⋯(lipophilic void)⋯(cage 2). The crystal studied was found to be a racemic twin.

In the crystal structure of the title compound, the cyclohexane ring of the H 3 L 3+ cation exhibits a chair conformation with the hydroxy group in axial and the three ammonium groups in equatorial position. Puckering parameters of the cyclohexane ring according to Cremer and Pople (1975) are Q = 0.588 Å, θ = 179.2 °, φ = 182.4 °. Due to the particular all-cis-configuration, the cation has an amphiphilic shape with a lipophilic (C 6 H 6 ) and a hydrophilic (OH, NH 3 + ) side. It is noteworthy that the lipophilic side of H 3 L 3+ is directly oriented towards the C 3 -axis, generating thus a lipophilic void with a trigonal geometry. This void is filled with a part of the hydrogen sulfate anion and the water of crystallization, both located either on, or close to, the threefold axis. The moieties within this void are all disordered (see the experimental refinement section). The crystal structure is basically made up by a complex net of N-H···Cl hydrogen bonds.
Additionally, the oxo oxygen atom O11 of the HSO 4anion accepts three H(-N) hydrogen atoms, and the hydroxy group (O2) of the H 3 L 3+ cation donates its proton to Cl3. O2 does, however, not act as an acceptor. A similar behaviour has recently been noted in related structures Neis, Merten & Altenhofer et al., 2012).
It is well known that the ability of axial hydroxy groups for forming hydrogen bonds is restricted on steric grounds (Bonnet et al., 2005). Cl1 has a coordination number of four with a distorted tetrahedral geometry. Cl2 also accepts four H(-N) hydrogen atoms. However, if the Cl2···O2W distance of 3.225 Å is interpreted in terms of an O-H···Cl hydrogen bond, the coordination number is five with a geometry intermediate between a trigonal bipyramid and a square pyramid (τ = 0.43). It must, however, be emphasized that O2W is only partially occupied and the hydrogen atom in consideration could not be located (see again the experimental refinement section). Cl3 and Cl4 (lying on the C 3 -axis) have both a coordination number of three with a trigonal pyramidal geometry.
Viewing the structure along the threefold axis, three distinct structural motives can be recognized. (i) Cl3 and Cl4 together with three symmetry equivalent H 3 L 3+ cations constitute a [(H 3 L) 3 Cl 2 ] 7+ cage, where Cl3 is hydrogen bonded to three hydroxy groups and Cl4 is hydrogen bonded to three ammonium groups of the three cations. (ii) The lipophilic void, formed by the C 6 H 6 -sides of three H 3 L 3+ cations has already been mentioned. The three cations are interlinked by three Cl2 ions via N-H···Cl···H-N hydrogen bonding. The disorder that is observed for the moieties within this void, is probably caused by the absence of suitable hydrophilic hydrogen acceptors. (iii) Three H 3 L 3+ cations together with a HSO 4and three Clcounter ions form a [(H 3 L) 3 Cl 3 (HSO 4 )] 5+ cage with the Clanions and three ammonium groups (N5) forming an almost planar, hydrogen bonded N 3 H 6 Cl 3 ring. Looking along the C 3 -axis, these three motives are arranged in supplementary materials sup-2 Acta Cryst. (2012). E68, o1899-o1900 the order cage 1 ··· lipophilic void ··· cage 2 ···.

Experimental
A hydrated sulfate salt (H 3 L) 2 (SO 4 ) 3 . 5H 2 O has been prepared following the protocol given by Merten et al. (2012) H 6.13, N 12.07. Single crystals were obtained from an aqueous solution of the sulfate salt which has been acidified with conc. hydrochloric acid to pH < 1. The solution was allowed to evaporate slowly at ambient conditions (295 K). Single crystals appeared after a period of several days.

Refinement
The H 3 L 3+ cation could be refined without problems, and its hydrogen atoms could all be located. They were treated as recommended by Müller et al. (2006): A riding model was used for H(-C) atoms. The positional parameters of the Oand N-bonded H-atoms were refined using isotropic displacement parameters which were set to 1.5×U eq of the pivot atom. In addition, restraints of 0.84 and 0.88 Å were used for the O-H and N-H distances. A total of four chloride positions were located; two of them (Cl3 and Cl4) are placed on the threefold axis, adding up altogether to a total charge of -2.667. Moreover, an SO 4 moiety was located on the three fold axis. Although a hydrogen atom could not be found in proximity to any of the sulfate oxygen atoms, charge balance considerations require that this moiety must be formulated as HSO 4 -(this is reasonable, if the acidic medium used for crystal growth is considered). In agreement with such an interpretation, two distinctly different S-O bond lengths were observed. O11, lying again on a threefold axis, forms a short S=O bond. O12, which forms a longer S-O bond, lies, however, on a general position. It appears thus that the hydrogen atom of the HSO 4ion is distributed over three symmetry equivalent sites, and O12 is occupied in a 33%: 66% ratio by a hydroxy and an oxo group, respectively. Such a disorder is also reflected by the relatively large displacement of O12. In proximity to the disordered hydrogen sulfate anion, two additional peaks, O1W and O2W, were localized and were interpreted as disordered water molecules. O1W was again located on the threefold axis, whereas O2W lies on a general position. The short O1W···O2W interatomic distance of 2.46 Å precludes a simultaneous occupation of both positions. The occupancies of O1W and O2W were therefore constrained to add up to a value of 100%. The refinement exhibited equal distribution of 50% each, indicating that either one water molecule on O1W or three water molecules on O2W are present, resulting in a H 3 L 3+ : H 2 O ratio of 3:2. Due to this disorder, it was again not possible to locate any hydrogen atoms, and the relatively large displacement of O1W and O2W was refined isotropically. The Flack parameter (1255 Friedel pairs) refined to a value of 0.41 (7), indicating formation of an inversion-twin with roughly equal portions of the two domains. As a consequence, the TWIN option of SHELXL was used in the final refinement resulting in a marginal drop of wR2 from 10.3 to 10.1%. In agreement with the Flack parameter, the BASF parameter was found to be 41%. program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2012); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009    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.  (3)