RESUMO
L-Leucinium hydrogen maleate crystals are very plastic at ambient conditions. Here it is shown that this plasticity is preserved at least down to 77â K. The structural changes in the temperature range 293-100â K were followed in order to rationalize the large anisotropic plasticity in this compound. To the best of our knowledge, this is the first reported example of an organic compound remaining so plastic at cryogenic conditions.
Assuntos
Leucina/química , Maleatos/química , Temperatura , Anisotropia , Cristalização , Estrutura MolecularRESUMO
The title 1:1 salt, C7H8NO2 +·C5H3N2O2 - (systematic name: 4-carb-oxy-anilinium pyrazine-2-carboxyl-ate), was synthesized successfully by slow evaporation of a saturated solution from water-ethanol (1:1 v/v) mixture and characterized by X-ray diffraction (SCXRD, PXRD) and calorimetry (DSC). The crystal structure of the salt was solved and refined at 150 and 293â K. The salt crystallizes with one mol-ecule of 4-amino-benzoic acid (PABA) and one mol-ecule of pyrazinoic acid (POA) in the asymmetric unit. In the crystal, the PABA and POA mol-ecules are associated via COOHâ¯Narom heterosynthons, which are connected by N-Hâ¯O hydrogen bonds, creating zigzag chains. The chains are further linked by N-Hâ¯O hydrogen bonds and π-π stacking inter-actions along the b axis [centroid-to-centroid distances = 3.7377â (13) and 3.8034â (13)â Å at 150 and 293â K, respectively] to form a layered three-dimensional structure.