A wide‐bandpass multilayer monochromator and its application to the determination of absolute structure

A diffraction system has been constructed at the Synchrotron Radiation Centre at Ritsumeikan University, in which a wide-band parallel X-ray beam is produced by reflection from the depth-graded multilayer monochromator. The band width is 600 eV and the monochromator is useful in the photon energy range from 6500 to 7700 eV. In diffraction patterns of an oscillating single crystal recorded using the beam, Bragg reflections appear in an elongated form on an imaging-plate detector and, if the absorption edge of an atom in the crystal is included in the band, a characteristic intensity profile is seen due to anomalous dispersion. As an application of the system, the absolute configuration was determined for a newly synthesized compound, 4-(1-hydroxyethyl)phenylferrocene, C18H18FeO, with an enantiomorphic structure, choosing the Fe atoms as anomalous scatterers. In the intensity profiles of the Friedel pairs of reflections, clear contrast between the pair was observed at the absorption edge, leading unequivocally to the S form. Further possible application of the wide-bandpass parallel beam is discussed.