supplementary materials

Research on supramolecular compounds has become popular because of their potential applications in areas such as gas storage (Rowsell et al., 2005), magnetics (Neville et al., 2008) and optics (Huang et al., 2007). Among many strategies for achieving supramolecular compounds with predefined structures, the choice and design of organic molecules as hydrogen-bond acceptors or donors are undoubtedly a key part of the construction of intriguing frameworks driven by hydrogen-bonding interactions (Burchell et al., 2006).

However, in these hydrogen-bond supramolecular compounds, 2-amino-pyridine often only forms co-crystals with another organic acid, such as 3-aminobenzoic acid, naphthalene-1,5-disulfonic acid and nicotinic acid (Jebas et al., 2006). It is less studied that the co-crystals are aggregated by 2-amino-pyridine with a non-acid compound. For example,non-acids compounds of saccharinate (Banerjee et al., 2006) and bis(methanesulfonyl)amide (Moers et al., 2000) have been used to form co-crystals with 2-aminopyridinium and their crystal structures have been reported.

Herein, we will give another report about the synthesis and chacterization of a 2:1 proton-transfer salt formed by 2-aminopyridinium with a non-acid compound of di(2-mercapto-1,3,4- thiadiazyl) disulfide and a water molecule.

Scheme I

The asymmetric unit contains one deprotonated di(2-mercapto-1,3,4-thiadiazyl) disulfide molecule, two protonated 2-amino-pyridine molecules and one water molecule. In the deprotonated di(2-mercapto-1,3,4- thiadiazyl) disulfide, two 2-mercapto-1,3,4-thiadiazyl groups are located at cis-position of the S3—S4 bond. In addition, these two 2-mercapto-1,3,4-thiadiazyl groups are in an opposite position with the dihedral angle between them being 6.84 (2)°. This geometry looks like that there is a C2 symmetric axis passing through the mid-point of the S3—S4 bond. The S3—S4 bond length is 2.06438 (11) Å, which is longer than that in dibenzothiazyl-disulfide [(2.027 (2) Å](Jian et al., 2006). All of the other bond lengths and bond angles in the two pyridyl rings and two thiazolyl rings are in the normal range.

In the crystal lattice, there are eight kinds of hydrogen bonds (Table 2), five of which link two 2-mercapto-1,3,4- thiadiazyl disulfide and four 2-amino-pyridinium ions together to form a macrocycle unit and three of which related to the water molecule help to conjunct all of the macrocycles to build a three dimensional net works of the molecules.

As shown in Fig. 2, after accepting a proton from 2-mercapto-1,3,4-thiadiazyl disulfide, 2-amino-pyridinium ion has become a complete hydrogen bond donor. For example, each of the 2-amino-pyridinium ion containing N4 atom provides its three hydrogen bond donor sites such as N4—H4A, N3—H3A and N3—H3B to participate in building hydrogen bonds with two deprotonated 2-mercapto-1,3,4- thiadiazyl disulfide molecules, and finally to form three hydrogen bonds of N4—H4A···N5, N3—H3A···S1 and N3—H3B···S6. Each of the 2-amino-pyridinium ion containing N2 atom provides two hydrogen bond donor sites of N1—H1A and N2—H2A to construct hydrogen bonds with one deprotonated 2-mercapto-1,3,4- thiadiazyl disulfide molecule, and ultimately to form two hydrogen bonds of N1—H1A···S6 and N2—H2A···N8. Through above hydrogen bond connections, four 2-amino-pyridinium ions and two deprotonated 2-mercapto-1,3,4-thiadiazyl disulfide molecules are join together to give a macrocycle unit. Then, each three macrocycle units are linked together by a water molecule through three hydrogen bonds of N1—H1B···O1W, O1W-H1W1···S6 and O1W-H2W1···N6. Namely, the water molecule acts as two hydrogen bond donor as well as one hydrogen bond acceptor to join three macrocycle units together. Additionally, since the existence of two S3—S4 bonds, each macrocycle is bended to two layers and in each macrocycle unit, there are six hydrogen bond sites to link with six water molecules. Thus, all macrocycles are connected by water molecules to construct a three-dimensional architecture. On the other hand, among the pyridyl and thiadiazyl rings, there are π···π stacking interactions (Table 2) which further stabilize the crystal packing.