Catching new modulated high-pressure phases of δ-chlorpropamide: when the experimental setup matters

The antidiabetic drug chlorpropamide [1-(4-chlorophenyl)sulfonyl-3-propylurea, CPA] has one of the highest numbers of reported polymorphs, making it an excellent model system for studying structural responses to pressure or temperature. The densest polymorph, δ-CPA, was probed by single-crystal X-ray diffraction at both laboratory and synchrotron facilities. A new high-pressure phase with tripled cell parameter b as compared with the ambient pressure phase was discovered. High-brilliance synchrotron sources and fast data collection strategies allowed us to also detect the formation of the intermediate incommensurately modulated phase at 2.37 (5) GPa. The experiments revealed the effect of the pressure-increasing protocol on the structure evolution on hydrostatic compression. The importance and necessity of conducting both laboratory and synchrotron experiments for the same compound when studying solid-state transformations is illustrated. The opportunities provided by synchrotron sources for studying phase transformations are discussed, together with specific characteristics of synchrotron experiments that should not be overlooked.