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Teaching commission news

[ORTEP
of the year]Figure 1: The ORTEP diagram that prompted the creation of the ORTEP of the Year (OOTY) award.
The 2nd edition of the IUCr Teaching Commission Newsletter is available online as an PDF file at www.iucr.org/iucr-top/comm/cteach/newsletters/2007nov/. The theme of this edition is based on the history of the ORTEP of the Year (OOTY) Award as written by its founder, Richard Harlow. While a crystallographer at Dupont, Richard describes the incentive behind creation of the award (see Figure 1) and gives an overall history with examples. These include two ORTEP diagrams where one diffraction dataset must have been collected on a windy day, and the other during a force ten gale. Following this article is a reprint (by permission of NIST) of Richard’s well regarded 1996 article on “Troublesome Crystal Structures: Prevention, Detection, and Resolution.”

[Structure shown to be not quite right]Figure 2: molecular diagram of a structure where IUCr validation checks indicate that structure is not quite right.
In the OOTY article’s conclusion, Richard notes, ‘One of my biggest concerns was the advent of refinement software which would allow even the most inexperienced people to restrain, constrain, and otherwise control each of the atomic thermal parameters. This clearly pointed to a future where it would be much harder, if not impossible, to detect incorrect structures directly from the ORTEP drawings. Every ORTEP drawing could now be made “perfect”.’ This comment finds relevance within the next article by Anthony Linden on “Crystallographic Data Validation - Ten Years On.” Besides a brief history and overview on the IUCr’s structure validation facilities, “minor” checkCIF alerts are elaborated as applied to some published imine structures. The molecular diagram of one such imine is given in Figure 2, and Anthony’s article elaborates on which and why one of the nitrogens is more likely an oxygen. One conclusion of the article is that even “minor” validation alerts should be carefully considered and pondered. Another is that traditional examination of ORTEPs and hydrogen-bonding diagrams should still be performed as “our eyes often reveal things to us that numerical data may not.”

Completing the newsletter’s articles on validation is one on the use of the Topas software for validation of a complex inorganic crystal structure using bond valence restraints by Ivana Radosavljevic Evans. In other articles, Patrick Carroll describes on online course in the fundamentals of X-ray crystallography to supplement a traditional lecture-type course. Zia Khan provides two articles on the history and challenge of teaching molecular symmetry, and crystallography in general to chemistry and physics students in Pakistan. Roxana Flacau discusses the combined Rietveld/MEM (Maximum Entropy Method) as implemented in the RIETAN-2000/PRIMA software with an example of the method being applied to the electron density analysis of high pressure phases using powder diffraction data.

[Radiation dose]Figure 3: Estimated radiation dose levels based on the known X-ray flux for a Copper sealed-tube (at its maximum power rate). Note the radiation dose at the tube-tower beam-port is in the region of ten million (107) rem/hr (100rem is 1Sv)
Finally is Joseph Reibenspies’ submission titled “X-ray Safety for Analytical Instrumentation: It’s what you cannot see or feel that will hurt you!” A nicely conceived diagram of expected radiation fields within a sealed-tube diffractometer is reproduced here as Figure 3. Commercial vendors of modern integrated diffraction equipment set extremely high standards of operator safety, however aging, poorly maintained or custom X-ray apparatus may be a different matter; especially if illegal ad-hoc modifications have occurred. Users of analytical X-ray apparatus are well advised to understand the hazards of high intensity X-ray beams; as well as modern safety regulations requiring full interlocked radiation enclosures to ensure there is no significant chance of the operator coming into contact with incident or diffracted X-ray beams.

The next edition of the newsletter is expected to be in mid to late 2009. Articles relating to crystallographic teaching, including historical, regional and national overviews, are very welcome and can be sent to the newsletter editor at lachlan.cranswick@nrc.gc.ca.

Lachlan Cranswick