The design of the crystals structure study. I. Optimization of data collection on modern diffractometers

The disadvantages of the “strategy” scan-lists for diffraction experiments created by the diffractometer software are shown. The reason for these disadvantages is that the traditionally used target function has a limited, local meaning, for example, to obtain the best coverage of the reciprocal space. An approach is proposed that implements the principle of statistical randomization of the experiment and makes it possible to achieve the strategic goal of structural analysis – obtaining a model capable of reflecting the subtle details of the atomic structure. A scan-list balanced by most factors has been found, which in less time leads to obtaining experimental data of significantly higher quality than traditional lists. The use of a reference crystal, previously measured dozens of times on diffractometers around the world, has shown the advantage of experimental data obtained by a new method. Increasing the balance and accuracy of the data resulted in a maximum improvement in the values of the refinement criteria to R1/wR2 = 0.53/0.59% and Δρ = –0.47/+0.30 e/ų. The achievement of the strategic goal of the research of the reference crystal (confirmation of the anharmonic model of atomic displacement parameters) could be confirmed not only by the “purification” of difference Fourier syntheses of electron density, which is sometimes visual and subjective, but also by a statistically flawless decrease in the R-factors of refinement by 30–40 relative %. Data of such high quality are needed to study the dynamics of structural models under external conditions, for the detection and modeling of phase transitions, critical points, bio- and chemical activity of compounds, verification of computational methods of structures.