Crystal structure of bis(1,4-diazabicyclo[2.2.2]octan-1-ium) thiosulfate dihydrate

The crystal structure of the title salt hydrate contains discrete DABCOH+ cations (DABCO = 1,4-diazabicyclo[2.2.2]octane), thiosulfate anions and lattice water molecules. The three molecular components are held together through hydrogen bonds.

The crystal structure of the hydrated title salt, 2C 6 H 13 N 2 + ÁS 2 O 3 2À Á2H 2 O, contains a centrosymmetric cyclic motif of eight hydrogen-bonded molecular subunits. Two DABCOH + cations (DABCO = 1,4-diazabicyclo[2.2.2]octane) are linked to two water molecules and two thiosulfate anions via O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen bonds, respectively. Two other water molecules close the cyclic motif through O-HÁ Á ÁO contacts to the first two water molecules and to the two thiosulfate anions. A second pair of DABCOH + cations is N-HÁ Á ÁO hydrogen bonded to the two anions and is pendant to the ring. Adjacent cyclic motifs are bridged into a block-like arrangement extending along [100] through O-HÁ Á ÁO interactions involving the second pair of water molecules and neighbouring thiosulfate anions.

Chemical context
The title thiosulfate was isolated accidentally when thioacetamide was mixed in ethanol with DABCO (1,4-diazabicyclo[2.2.2]octane), leading to the formation of the thiosulfate anion in situ.

Structural commentary
The asymmetric unit ( Fig. 1) consists of one thiosulfate anion, two monoprotonated DABCOH + cations and two water molecules. The thiosulfate anion exhibits approximate C 3v symmetry. However, in the crystal it has C 1 symmetry with S-O distances in the range 1.4688 (8) to 1.4898 (8) Å and an S-S bond length of 2.0047 (4) Å , and O-S-O and S-S-O angles ranging from 107.47 (4) to 110.48 (5) . In both DABCOH + cations, the three N-C bonds involving the protonated N atom are elongated [mean value 1.499 (2) Å ] compared to the three N-C bonds involving the non-protonated N atoms [mean value 1.472 (4) Å ].

Supramolecular features
The thiosulfate anion is linked via charge-assisted N-HÁ Á ÁO hydrogen bonds to two DABCOH + cations. The third oxygen atom (O2) of the anion acts as a hydrogen-bond acceptor for ISSN 2056-9890 one of the water molecules (O4). The second hydrogen bond involving this water molecule is directed towards a symmetryrelated thiosulfate anion. The second water molecule (O5) is the donor of one O-HÁ Á ÁO hydrogen bond to the other water molecule and of one N-HÁ Á ÁO hydrogen bond to one of the DABCOH + cations. Numerical details of the hydrogenbonding interactions are given in Table 1. This arrangement leads to the formation of a centrosymmetric cyclic motif consisting of eight hydrogen-bonded molecules with two pendant DABCOH + cations (Fig. 2). Adjacent cyclic motifs are bridged through O4-H44Á Á ÁO3 contacts into supramolecular blocks running along [100] (Fig. 3).

Synthesis and crystallization
Crystals suitable for a single-crystal X-ray diffraction study were isolated from a clear ethanolic solution of thioacetamide and DABCO in an equimolar ratio. Symmetry codes: (i) x À 1; y; z; (ii) Àx; Ày þ 1; Àz þ 1.

Figure 3
View of three successive hydrogen-bonded cycles displayed in red, blue and green. Pendant DABCOH + cations are shown in orange. H atoms not involved in hydrogen bonding (black dotted lines) are omitted for clarity.

Figure 1
The asymmetric unit of (I), with displacement ellipsoids drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines.

Figure 2
View of the content of one unit cell, showing the hydrogen-bonded macrocycle made up from the asymmetric unit and its inversionsymmetry-related counterpart. H atoms not involved in hydrogen bonding (black dotted lines) are omitted for clarity.