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Crystallography in Latin American seems to have started in the mid 1930s after the pioneering work of Ernesto Galloni, in Argentina. Since then, Crystallography was associated with undergraduate research and conducted in Departments or Institutes of Physics and Chemistry and later in Molecular Biology and Materials Science Departments. Most undergraduate degree programs required carrying out a research project for one or two semesters, writing a thesis, and making a public presentation of the work before a committee. Even after graduate degree programs started and began to consolidate, undergraduate degree research in Crystallography maintains its importance. The expertise and dedication of many Latin American crystallographers, most of whom graduated or visited important academic institutions in Europe and the US, created the foundations of our discipline in the region. For instance, after a work visit paid to Prof. B.E. Warren (MIT), Dr. Carlos Graef Fernández organized and taught the landmark course "Rayos X y Física Cristalográfica", at UNAM (Mexico) in 1947. Since then, the efforts of distinguished crystallographers, such as Galloni, Cano Corona, Fabregat Guinchard, Witke, Caticha-Ellis, Becka, Mascarehnas, among others, with support from UNESCO, IUCr, TWAS, and other institutions, helped to establish the tradition of teaching crystallography. In numerous courses, Ewald, Buerger, Hauptman, Karle, Woolfson and other prominent crystallographers participated as instructors. Many crystallographers helped to establish laboratories outside their countries of origin. In 1967, Amzel, Becka, and Baggio, worked at UCV, in Caracas, Venezuela, supervising undergraduate degree thesis based on crystallographic work. Later, Eldrys de Gil, after graduation from UCV, founded the Crystallography Laboratory of ULA (Mérida, Venezuela) which this year celebrates its 45 anniversary. An overview of key recent educational events and modern practices in Latin America will be presented.
abstracts
The need for improving the description of structural features with better quality data, at low temperature and with modern 2D detectors of certain materials, sometimes leads to surprisingly new insights into a previously reported structure. When attempting to grow single crystals of maleamic acid, good crystals of ammonium maleate, NH4(Mal), were obtained. Although the structure of this material has been reported at room temperature, in space group Pbcm with V=613.2(5) Å3 [1], synchrotron data were collected at low temperature to examine the behavior of the ammonium moiety. The data collected lead to a structure better described in Pbca, a=8.9687(12), b=8.1604(8), c=16.348(2) Å, V=1196.5(2) Å3, Z=8. The refinement converged to R=0.0438, wR2=0.1156, S=1.02. An examination of the new data indicates that reflections with h odd are systematically weak but, nevertheless, present. The Ca derivative of valproic acid (a common anticonvulsant) was reported as monoclinic, C2/c, with a=16.250(8), b=18.471(17), c=7.729(7) Å, β=109.71(5)0, V=2183.97 Å3, Z=4, and R=10.94% [2]. However, data collection at room temperature and under a stream of nitrogen on several newly prepared crystals always lead to a triclinic, P-1 cell, with approximately half the volume of the reported cell. Attempts to index the dataset using the known monoclinic cell resulted in high uncertainties for the unit cell parameters and high Rint values since reflection spots showed splitting and diffuse scattering. The new cell had dimensions a=7.6995(4) Å, b=11.7444(6) Å, c=11.7708(6) Å, α=91.089(3)0, β=101.643(3)0, γ=102.041(3)0, V=1017.47(99) Å3, Z=2. Although the initial refinement was discouraging (R=0.1172, wR2=0.360, S=1.12) the analysis with PLATON indicated the presence of twining and, after considering the twin law, the refinement improved significantly (R=0.059, wR2=0.1472, S=0.99). Several examples where a new data collection resulted in interesting results will be presented.
