[8.8.8]hexacosane monohydrate clathrate trichloride hexahydrate

The small cryptand 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane is a versatile host for cations (Coyle et al., 1997, 2004; McKee et al., 2001) and also, in the hexaprotonated form, for anions (Dietrich et al., 1996; Hossain et al., 2002). In this paper, we report the structure, (I), of a triprotonated form of the cryptand, which encapsulates a neutral water molecule as guest in the cavity. A similar complex formed from the tetraprotonated ligand has been reported recently (Hossain et al., 2002).

The title compound, C 18 H 59 N 3 8 Á3 Cl À Á7H 2 O, is a chloride salt of a triprotonated cryptand. One of the water molecules is located inside the crypt and makes six hydrogen bonds to the crypt (two as donor and four as acceptor). The coordination geometry about the bound water molecule is trigonal prismatic.
The structure of the [C 18 H 59 N 8 (H 2 O)] 3+ cation is shown in Fig. 1. H atoms bonded to O or N atoms were located in difference maps. The highest residual peaks are in the region of the chloride anions and not close to the amines; the protonated amines are N3B, N4A and N4C. The water molecule makes six hydrogen bonds to the cryptand (Table 1), two as donor (to N3A and N3C), and four as acceptor (from the three protonated amines and from N4B). These hydrogen bonds cover a wide range [2.680 (2)±3.022 (2) A Ê ]; the shortest are those where the encapsulated water molecule acts as donor to the neutral amines N3A and N3C, and the longest is that with neutral amine N4B as donor. Taken in isolation, it is surprising that the shortest hydrogen bonds are not the charge-assisted interactions involving the protonated amines; however, this is likely to be due to mutual constraints within the extended hydrogen-bond network (Fig. 2). All the secondary amine groups, protonated or not, make two hydrogen bonds, one to the central water molecule (O1) and the other to either a chloride anion or a water molecule of crystallization (Table 1). Within each of the three clefts formed by the cryptand is an amine±chloride±water±amine hydrogen-bonded chain and the hydrogen bonding extends in three dimensions throughout the crystal structure.
The coordination geometry at the encapsulated water O atom (O1W) is close to trigonal prismatic (Fig. 2). The arrangement of the six hydrogen bonds is remarkably similar to that observed for the encapsulated water molecule in the tetraprotonated analogue [C 18 H 60 N 8 (H 2 O)] 4+ , although in that case (Hossain et al., 2002) the geometry was described as tetrahedral.

Experimental
The unsubstituted cryptand was prepared as described previously (Smith et al., 1993). The protonated product was obtained in an attempt at part-tosylation of the amine N atoms. To one millimole of free cryptand in dichloromethane (50 ml) was added 4-methoxybenzene sulfonyl chloride (4 mmol) and triethylamine (4 mmol). The mixture was stirred overnight and evaporated to dryness. The white solid obtained was redissolved and subjected to alumina chromatography using as eluant dichloromethane/1% MeOH, which had been treated with ammonia gas beforehand. The crystals were obtained on slow evaporation of the eluant.

Figure 2
The hydrogen bonding about the cryptate (dashed lines); displacement ellipsoids for the Cl and O atoms are drawn at the 50% probability level.
[Symmetry codes: H atoms bonded to C atoms were placed at calculated positions and re®ned using a riding model. The CÐH distances were constrained to 0.99 A Ê and were re®ned with U iso (H) = 1.2U eq (C). H atoms bonded to O or N were located in difference maps and assigned a common U iso (H) value of 0.05 A Ê 2 ; their coordinates were re®ned freely, except that DFIX restraints were applied to the OÐH distances [0.84 (2) A Ê ] and HÐOÐH angles [by restraining the HÁ Á ÁH distances to 1.37 (1) A Ê ] (Sheldrick, 2001).
We are grateful to BBSRC for funding (DF) and to the Leverhulme Trust for an Emeritus Fellowship (JN). 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 N1