Incomplete Absorption Correction Results in an Increased Positive Mean Value of Weighted Residuals

Incomplete absorption correction procedures in single-crystal diffraction experiments leave a characteristic trace—a “fingerprint”—in the residuals. Specifically, weak intensities are systematically overestimated, contributing disproportionately and sometimes even dominantly to the chi-square sum in least squares refinements. An analysis of six published crystal structures spanning a wide range of absorption coefficients reveals a consistent positive shift of the weighted residuals, which were significant for crystals with >5.02 mm−1. This shift is all the stronger the greater the absorption coefficient and is accompanied by a proportionally increasing fraction of positive excess residuals. The simultaneous increase in the mean value of the residuals and the fraction of positive excess residuals proves that the shift is not caused by strong reflections or isolated outliers, but rather by the systematic overestimation of many weak intensities. Diagnostic plots and statistical metrics are presented for additional published data sets, supporting the generality of the findings. These findings can support the development of improved methods for absorption correction, which lead to physically meaningful thermal motion parameters even with strong absorption.