Diisopropyl{2-[2-(2-oxopyrrolidin-1-yl)acetamido]ethyl}ammonium hydrogen sulfate

The structure of the title compound, C14H28N3O2 +·HSO4 −, a nootropic drug (pramiracetam) investigated for cognition-enhancing properties, is closely similar to that of the previously determined acetonitrile solvate, both structures being characterized by the presence of ribbons of hydrogen-bonded ions. The pyrrolidine ring adopts an envelope conformation.

The structure of the title compound, C 14 H 28 N 3 O 2 + ÁHSO 4 À , a nootropic drug (pramiracetam) investigated for cognitionenhancing properties, is closely similar to that of the previously determined acetonitrile solvate, both structures being characterized by the presence of ribbons of hydrogenbonded ions. The pyrrolidine ring adopts an envelope conformation.
The contents of the asymmetric unit of the title compound (I) are shown in Fig 1. The atomic labelling is consistent with that previously adopted for the CH 3 CN solvate (Bandoli et al., 1987) with which (I) is isomorphous and substantially isostructural, although the present conventional choice of labels for the axes does not match that of the previous report. There is a 3.8% reduction in the cell volume going from the solvated form to the present one, due to contraction of the two longest cell axes. The packing (Fig. 2) is controlled by a network of hydrogen bonds. The HSO 4 anion behaves as a hydrogen bond donor towards a carbonylic oxygen and acts as acceptor of two hydrogen bonds from the aminic and ammonium N atoms (details of hydrogen-bonding geometry have been provided in Table 1). In this way two centrosymmetric and adjacent loops, consisting of 14 and 18 non-hydrogen atoms, respectively, are formed. Each loop has contributions from parts of two anions and two cations and each of these ions contributes to two contiguous loops which share the N2-H2···O3-S strand.
Such arrangement, combined with the operation of the c translation, generates ribbons in the structure (these were parallel to the a direction in the previously reported structure of the solvated form, due to the different labelling of cell axes). In the case of the CH 3 CN solvate the solvent molecules occupy large voids among the ribbons and are not involved in the network of hydrogen bonds. The largest difference in the conformation of the cation between the two structures is found for the C1-N1-C5-C6 torsion angle, whose value of -94.6 (2)° for (I) is significantly smaller than that, of -105.4(1.2)°, found for the structure of the solvate. The structure of (I) is stabilized by non-classical intermolecular and intramolecular hydrogen bonds of the type C-H···O (Table 1).

Experimental
Samples of pramiracetam were kindly provided by SIMS (SIMS srl, Reggello Firenze, Italy). Crystals of (I), suitable for X-ray diffraction analysis, were obtained by slow evaporation from 1:3 2-propanol:acetone solutions.

Refinement
A small fraction of data is missing from completeness because the structure appeared to be monoclinic at the time of data collection. It was impossible to collect a new set of data due to extreme difficulty to obtain suitable material for diffraction.
Also, since crystals did not diffract strongly, it was deemed that collecting data at θ higher than 72° would not yield significant the O and S atoms of the counterion. The existence of voids (57.0 Å 3 ) in the structure is likely due to the stability of the hydrogen-bonds framework, as the solvents used for crystallization could not fit into the available spacing. Fig. 1. A view of the content of the asymmetric unit of (I). Displacement ellipsoids are drawn at the 50% probability level.