Chiral and achiral crystals, charge-assisted hydrogen-bond patterns and self-organization of selected solid diaminium...

A series of diaminium thiosulfates, derivatives of diamines: NH₂CH₂CH(CH₃)NH₂ (1) and NH₂(CH₂)_nNH₂, n = 3-6 [(2)-(5)] and thiosulfuric acid were prepared and their structures determined by single-crystal X-ray diffraction analysis. Compounds (1), (2) and (4) turned out to be hydrates. The crystal structure of 1,2-propylenediaminium thiosulfate is chiral and exhibits spontaneous resolution. Crystals for both enantiomers [(1a) and (1b)] were obtained with high enantiometric excess and examined. An extended network of strong, charge-assisted hydrogen bonding of the ⁺N-H...O^- type (also O-H...O and O-H...S for hydrates) is most likely the main factor defining crystal packing and the variable conformation of the cations. The formation of chiral hydrogen-bond motifs - distorted cubans - seems to induce the formation of chiral solid-state structure from achiral components in the case of (4). Diaminium thiosulfates with an odd number of C atoms in the alkyl chain [compounds (1), (2) and (4)] form three-dimensional supramolecular networks, while in the case of diaminium salts with an even number of C atoms [(3) and (5)], two-dimensional layers of hydrogen-bond domains are observed. The aminium thiosulfates were also characterized by elemental analysis, NMR and Fourier transform (FT)-IR spectroscopy. The conformations of α,ω-alkyldiaminium cations in the solid state are discussed and rationalized by DFT calculations.