W0269

Structure Determination from Powder Diffraction Data – Challenging Open Framework Materials. Peter Y. Zavalij and M. Stanley Whittingham, Institute for Materials Research and Dept. of Chemistry, SUNY-Binghamton, Binghamton, NY 13902-6000.

Crystal structure determination from powder data (SDPD) is not a straightforward process because of the accuracy in integrated intensity that is due to the peaks overlapping, preferred orientation and other factors. It is even more challenging in case of open framework materials, where those factors are intensified and often unavoidable.

In recent years, we have been involved in developing new materials that can be used as a cathode in rechargeable lithium batteries. These materials have usually open framework structure, mostly layered, which along with often relatively low crystallinity and inability to grow crystals provide additional challenges for SDPD. Nevertheless, ab-initio crystal structure solution was successfully used to determine the crystal structure of over 15 compounds.

This presentation summarizes the results of solving structures from powder data and discusses problematic cases. Most of the structures were challenging in many different ways: ab-initio indexing in the presence of other phases; powder pattern decomposition with substantial peak broadening at elevated angles; preferred orientation correction (prior to solving structure) and refinement (several different axes). Of course the main challenge was solving the structure that was done using different methods: direct (automatic) or heavy atom (manual), geometry optimization (DLS) or energy minimization (DMol), but always involving de facto or a priori chemical and structural knowledge as well as any available analytical data.