Putrescinium Sulfate: A Low Temperature Study of Disordered, Non-Symmetric Molecule in a Special Position

Abstract

The structure of butane-1,4-diaminium sulfate, C4H14N2 2+ × SO4 2− is, in both room temperature and 100 (1) K, an example of the centro–non-centrosymmetric ambiguity in the crystal structure determination. It is possible to solve and successfully refine this structure in Pnma and Pna2 1 space groups, with slightly better results obtained for the centrosymmetric group. In both models the cation is disordered over two positions, the ordered terminal nitrogen atoms are connected with two disordered aliphatic chains that cross each other in the middle of the central C–C bond, at the pseudo-inversion center—although the cation itself is not symmetrical—in case of the centrosymmetric model. In this model, the anion is also situated in the special position, on the mirror plane. The conformations of two alternative forms of the cation are not fully extended, as it is often the case for simple salts of linear α,ω-diamines, but trans-gauche-gauche. Each of amine groups displays the same N–H···O hydrogen bonding patterns, with two single and one bifurcated hydrogen bonds. These hydrogen bonds connect the ionic species into rings and further into alternating waved layers. The room-temperature structure of this salt has been reported recently (van Blerk and Kruger J Chem Crystallogr 38:175–179, (2008)), the present analysis adds the low temperature data, and–what is more important—the different description of the disorder, the refined positions of N–H hydrogen atoms and the discussion of centro- non-centro ambiguity. Crystal data: crystal system: orthorhombic, a = 9.9722 (4) A, b = 9.4675 (4) A, c = 8.6532 (4) A, space group: Pnma, V = 816.96 (6) A3, Z = 4. The cation is disordered over two positions, the ordered terminal nitrogen atoms are connected with two disordered aliphatic chains that cross each other in the middle of the central C–C bond, at the pseudo-inversion center—although the cation itself is not symmetrical—in case of the centrosymmetric model.