High Z′ Crystal Structure of a New Polymorph of a Thioimidazole Disulfide: Importance of Conformational Flexibility

A new polymorph of a thioimidazole disulfide (2- [(1H-imidazol-2-yl) disulfanyl]-1H-irnidazole; IDI) was prepared, which exhibits a rare crystal structure with 4 symmetry independent molecules (Z' = 4; Z = 16) and all possible conformers predicted for the isolated molecule within the crystal unit cell. The crystal structure is non-centrosymmetric, Ia monoclinic space group, with cell parameters: a = 7.45910(10) angstrom, b = 44.1680(8) angstrom, c = 11.3522(2) angstrom, and beta = 103.0240(10)degrees. The four symmetry independent molecules establish an extensive hydrogen bond network involving NH groups as proton donors and N atoms of neighboring molecules as acceptors. A computational structural investigation of the isolated molecule of the compound was performed at the DFT(B3LYP)/6-311++G(d,p) level of theory in order to characterize in detail its conformational space, and these results were taken into account to evaluate the role of conformational flexibility and intermolecular interactions in the observed crystal packing. The exceptional structural characteristics of the new polymorph were underlined by comparison with those of the previously reported one (C2/c, monoclinic, Z = 4; Z' = 1/2; Bazargani, M. F.; Talavat, L.; Naderi, S.; Khavasi, H. R. Acta Crystallogr., Sect. E 2011, 67, o2585).