Di-2-pyridyl disulfide–succinic acid (1/1)

In the title compound, C10H8N2S2·C4H6O2, both components of the cocrystal lie on crystallographic twofold rotation axes. In the di-2-pyridyl disulfide molecule, the dihedral angle between the two pyridine rings is 66.6 (1)°. In the crystal structure, intermolecular O—H⋯N and weak C—H⋯O hydrogen bonds link both types of molecules into columns along the c axis.

In the title compound, C 10 H 8 N 2 S 2 ÁC 4 H 6 O 2 , both components of the cocrystal lie on crystallographic twofold rotation axes. In the di-2-pyridyl disulfide molecule, the dihedral angle between the two pyridine rings is 66.6 (1) . In the crystal structure, intermolecular O-HÁ Á ÁN and weak C-HÁ Á ÁO hydrogen bonds link both types of molecules into columns along the c axis.

Comment
The design of cocrystals has been a field of intensive research in recent years. With reliable design strategies, cocrystals could offer a modular approach to developing materials with desirable properties. (Desiraju, 2003;Thalladi et al., 2007).
Weak noncovalent interactions such as hydrogen bonds are utilized to create cocrystals. Herein we report the structure of the title cocrystal.
The formula unit of the title compound ( Fig. 1) contains one molecule of di-2-pyridyl disulfide (dpds) and one molecule succinic acid. The dihedral angle between the two pyridine rings of the dpds molecule is 66.6 (1)°, and the S-S bond length, 2.025 (2) Å, is not significantly different than that found in the structure of the free ligand, 2.016 (2) Å (Raghavan et al., 1977). The torsion angle of the C6-C7-C7 ii -C6 ii [symmetry code: (ii) -x, y, -z+3/2] backbone of succinic acid is 74.5 (3)°. The proton of the carboxylate O atom (O2) of the succinic acid molecule forms a strong hydrogen bond with atom N1 of the dpds molecule (see Table 1 for hydrogen bond geometry). In addition, in the crystal structure, weak intermolecular C-H···O hydrogen bonds supplement intermolecular N-H···O hydrogen bonds to form columns running parallel to the c-axis (Fig 2).

Experimental
All chemicals were reagent grade quality obtained from commercial sources and without further purification. Dpds (0.2206 g, 1 mmol) and succinic acid (0.1181 g, 1 mmol) were dissolved in a H 2 O/EtOH solution (v/v = 2:1, 15 ml), which was stirred for 0.5 h and then filtrated, the filtrate was allowed to concentrate by slow evaporation to give colorless block crystals.