1 , 4-Diazabicyclo [ 2 . 2 . 2 ] octane ( DABCO ) 5-aminotetrazolates

The crystal structures of four salts of 1,4-diazabicyclo[2.2.2]octane (DABCO) and 5-aminotetrazole are described. Anhydrous 1:1 (Pbca, Rgt = 0.041) and 1:2 (P 1 , Rgt = 0.038) salts form hydrogen-bonded layers of anions and cations. The monohydrate of the 1:1 compound (P21/c, Rgt = 0.038) shows infinite chains of DABCO cations and an undulated layer of anions and water molecules. The octahydrate of the 3:2 compound (P21/c, Rgt = 0.042) features DABCO triples and clusters of four tetrazolate ions in a network of water molecules.

Continuing our interest in DABCO salts [21] and hydrates [22] we decided to explore combinations of DABCO and 5-aminotetrazole.

Results and Discussion
The DABCO molecules typically adopt a cage-like structure. The aminotetrazole molecules are planar (largest deviation 0.023 Å). The four new salts contain DABCO monocations in different arrangements. In all cases, association among the aminotetrazole molecules is observed. Hydrogen bond interactions between cations and anions are found only in the anhydrous salts, whereas the hydrates show preferred interactions between anions and water molecules. Crystal data and details of the structure refinement are summarized in Table 1. Hydrogen bond parameters are shown in Table 2.

1-Aza-4-azoniabicyclo[2.2.2]octane 5-aminotetrazolate (1)
In this most primitive salt of DABCO and aminotetrazole, the aminotetrazolate anions form ribbons parallel to the (0 1 0) plane, assembled from nine-membered rings and propagating in the direction of the crystallographic a axis. The DABCO cations are attached to the edges of the ribbons by hydrogen bonds (Figure 1).

1-Aza-4
It is inter The aminote esulting net his aestheti and water m

Bis(1-az Octahydrate
Small cry data/parame structure is nvolving tw water molec a cloud of w

Synthesis of DABCO 5-Aminotetrazolates
DABCO (0.56 g, 5 mmol) and the appropriate amount of 5-aminotetrazole were dissolved in MeOH (3 mL). For the hydrate, the required amount of H 2 O was added. The solution was slowly refrigerated to -20 °C. After 3 days the supernatant was discarded, and the crystals were collected.

Crystal Structure Determination
Intensity data were recorded with Oxford Diffraction Gemini-R Ultra and Nonius KappaCCD diffractometers using Mo K radiation. Experimental details are summarized in Table 1. Structure solution and refinement was performed with the programs SIR2002 (direct methods) [28] and SHELXL-97 [29]. CCDC reference numbers: 855697-855700. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.

Conclusions
Assembly of simple but versatile building blocks offers a treasure trove of opportunities and rich rewards for the curious investigator. The structures described herein are impressive examples of this successful concept.