MS20-P03 Scope and limitations on refinement strategy. Service Crystallographer’s publishing woes Arkady Ellern (Chemistry Department. Iowa State University, Ames, Iowa, United States of America)email: ellern@iastate.eduSmall molecule X-Ray structure determination can be considered as a three step process where each step is dependent the previous one.
Data collection. All special techniques (unstable samples, low temperature, high pressure experiments etc.) were well established many years ago. The revolution in computing during the last two decades speed up this step significantly as modern diffractometers with power radiation sources can collect full-sphere data with high redundancy in a few hours. As a result this step nowadays is absolutely routine in all specialized facilities.
Structure Solution/Refinement. “Black-box”, like Bruker EXPRESSO, obtains good results for simple samples by users without sufficient background in symmetry, crystallography, diffraction, refinement and even chemistry. However, in real life the majority of structures must be resolved unambiguously only by experienced professionals to consider the best route and final point of analysis, which is not always obvious and beyond a reasonable doubts.
As an example, giant spherical keplerate cluster structures like {Mo72V30} require a lot of restrains to model the disorder during the refinement to hold outer and inner ligands at reasonable positions and with acceptable temperature factors. The concomitant difficulties are: the split positions for metal core, the huge voids filled with diffused water solvent, uncertainties in the valence state of metals and occupancy of counter-ions. Where is the limit of data “massaging” and “fixing” on the way of supporting our model of choice?  Where should we stop?
Majority of customers use X-Ray structure determination for the qualitative and quantitative analysis which means they are fully satisfied with the connectivity table to assure the synthetic path and the proof of obtaining the target substance. How far should we go with such structures? The refinement for the simple metallo-organic complex can illustrate how stepwise split of disordered benzene solvent position influence the geometrical and thermal parameters of the main cluster.
Publication. Can we trust old X-ray structural results even though they can hardly pass the new strict requirements for publication? How many different expert opinions can we have on one simple structure like [Cr3(C3H5O2)6O(H2O)3]NO3 x 0.5H2O and what is wrong with publishing questionable (or even unintentionally wrong) results? Should we still describe the structure in a paper if we must supply CIF with all intensity/refinement data? Why one might still consider service crystallographer as a valuable co-author of publication? Let us try to get a consensus on those and some other questions
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Keywords: refinement, publication, checkcif