A low-temperature determination of triethylene-diaminium dichloride dihydrate

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved The structure determination at 150 K of triethylenediaminium dichloride dihydrate (also know as 1,4-diazaoniabicyclo[2.2.2]octane dichloride dihydrate), C6H14N2 2+ 2Cl 2H2O, obtained as part of an experimental polymorph screen on guanine, is reported here. The packing consists of a hydrogen-bonded chain structure, with one of the water molecules of crystallization involved in weak O—H Cl contacts.

The structure determination at 150 K of triethylenediaminium dichloride dihydrate (also know as 1,4-diazaoniabicyclo[2.2.2]octane dichloride dihydrate), C 6 H 14 N 2 2+ Á2Cl À Á2H 2 O, obtained as part of an experimental polymorph screen on guanine, is reported here. The packing consists of a hydrogen-bonded chain structure, with one of the water molecules of crystallization involved in weak O-HÁ Á ÁCl contacts.

Comment
Triethylenediamine, also known as 1,4-diazabicyclo[2.2.2]octane, is a strong base allowing protons to be removed from other compounds to give anionic intermediates. Triethylenediamine has two reported anhydrous polymorphs, a roomtemperature phase (Nimmo & Lucas, 1976a) and a hightemperature phase (Nimmo & Lucas, 1976b). This hightemperature structure assumes a 'plastic' phase, and is of interest as triethylenediamine is a one of a select group of globular molecules which undergo thermal transitions to plastic crystals because of the high degree of molecular mobility which can be achieved in the solid state (Weiss et al., 1964). There are also a number of co-crystals of triethylenediamine, including with hydroquinone (Mak et al., 1984), sulfate hemihydrate (Jayaraman et al., 2002), and bis-(hydrogen oxalate) (Vaidhyanathan et al., 2001). In addition, there are also triethylenediamine salts, including the dihydrochloride (Kennedy et al., 1987) and hydrobromide (Katrusiak et al., 1999). In this paper, we report the dihydrochloride dihydrate salt, (I), of triethylenediamine.
In (I), atoms N1 and N2 are both protonated, with the molecule in a slightly twisted conformation, different from the symmetric cage-like structure present in the room-temperature anhydrous crystal structure of unprotonated triethylenediamine (Nimmo & Lucas, 1976a). The bond lengths and angles are within expected values (Allen et al., 1987), with the C-N bond lengths in the range 1.4942 (15)-1.5009 (15) Å , and the C-C bond lengths in the range 1.5227 (17)-1.5368 (16) Å .
The packing consists of a hydrogen-bonded chain structure (Fig. 2), with atom N2 hydrogen bonded to O2W, through an N-HÁ Á ÁO hydrogen bond (Table 1). Water atom O2W acts as a hydrogen-bond donor to both Cl1 and Cl2, through O-HÁ Á ÁCl hydrogen bonds ( Table 1). The ion Cl1 is also hydrogen bonded through an N-HÁ Á ÁCl interaction to the N1 amine group, forming the chain motif. The O1W water of crystallization forms weak hydrogen bonds to Cl2, as shown in Table 1.

Experimental
As part of an experimental polymorph screen on guanine, (I) was obtained from a saturated solution of triethylenediamine in dilute hydrochloric acid, in which approximately 0.03 g of guanine was added in an attempt to crystallize this purine base. The solution was stirred, filtered, then evaporated at room temperature (10 ml solution, in 75 Â 25 mm vessels). Colourless block-shaped crystals of (I) were formed over a number of weeks. It should also be noted that large block-shaped crystals of triethylenediamine dihydrochloride were also obtained (Kennedy et al., 1987).
The triethylenediaminium H atoms were placed in geometrically idealized positions and allowed to ride on their parent atoms, whilst the water H atoms were refined, with O-H and HÁ Á ÁH distance restraints of 0.84 Å and 1.33 (2) Å , respectively.

Figure 2
The packing in (I), showing the hydrogen-bonded chain structure. The hydrogen bonds with DÁ Á ÁA > 3.2 Å have been omitted for clarity.

Figure 1
View of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.  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.