Phase determination and extension using X-ray multiple diffraction and the maximum-entropy method

The extension of the phases of the structure factors of the organic crystal C25H25NO2 from 77 starting individual phases using the maximum‐entropy method is reported. These starting phases were determined from 90 experimental triplet phases calculated from 215 measured ‐scan three‐beam and four‐beam diffraction profiles obtained with a rotating‐anode X‐ray source, where the scans were around the reciprocal‐lattice vectors of the 001, 002 and 003 reflections. The extension of the structure factors with phase values was carried out using the maximum‐entropy method for 2040 measured two‐beam Bragg diffraction intensities with 77 starting phases and the symmetry of the space group as the constraints. Use of structure‐factor triplets as constraints for entropy maximization was also attempted. The minimum χ2 criteria were applied to the maximum‐entropy extrapolation to discern the best phase set to be used as the new constraints for the next step of generating new phases. With this phase‐extension procedure, more than 100 phases were determined and an electron‐density map at 1.97 Å was deduced.