Solid-State Reactions of Molecular CrystalsBruce M. Foxman, Brandeis University, DMR 0504000

In 1968 Professor Keith Prout (Oxford University) synthesized diaquabis(2-hydroxy-2-propionato)copper (I, below). The complex crystallized in space group C2/m. Unfortunately, the structure solution could not be completed at that time, and featured very large anisotropic displacement parameters. Professor Prout called this problem to our attention 20 years ago, as the crystals were also radiation-sensitive, but we were unable to make significant progress until this year, at last putting to rest a 40-year old literature problem.

Using our new Apex2 Kappa CCD diffractometer, undergraduate Ben Heyman could readily reproduce the “problem structure”. Mr. Heyman found a phase transition at -3 ºC that leads to an ordered phase (II). The carboxylate ligands in the ordered phase are not as rigorously “planar” as in I, and it is apparent that I is a disordered and twinned composite of II with C2h symmetry, to give an average structure with the appearance of I. Finally, screening of numerous crystals shows that II may be also be obtained as a polymorph at room temperature without cooling!

I II

Solid-State Reactions of Molecular CrystalsBruce M. Foxman, Brandeis University, DMR 0504000

Their crystals of sucrose, one of the suggested materials in the tutorial, were not suitable for X-ray diffraction purposes, but they had grown beautiful crystals of another substance, cupric chloride dihydrate. A crystals was selected, cut to size, and checked with polarized light; all the students had the opportunity to observe this procedure. Data collection and structure solution were accomplished in just over an hour’s time. The demonstration was followed by a tour of Brandeis' Chemistry Department, and a discussion of possible science career paths, with emphasis on Chemistry or how Chemistry relates to other disciplines. All in all, a very successful day!

Education & Outreach: Last year Prof. Foxman, along with local high school teachers Michael Vela (Concord-Carlisle Regional High School) and Tae Cho (Sharon High School) conceived and wrote a tutorial, Crystalline Insights, with the advanced high school science student in mind. Since most high school chemistry classes only briefly discuss aspects of crystal structure, the goal of the tutorial is to extend the subject to a demonstration of the practical operations of X-ray diffraction and structure determination. Version 1.0 of the tutorial contains > 110 PowerPoint "slides” and many external links.  Connection to the internet is not required, as all external links are included with the distribution. Copies of the tutorial are available at http://www.xray.chem.brandeis.edu .

Science teachers Catherine Botsford-Milne and Bert Gardner of Attleboro High School, along with 30 students, downloaded and tested the tutorial in June 2007, grew crystals, and came to the Brandeis facility on 14 June 2007.