Materials containing disordered moieties and/or amorphous or liquid-like phases or showing surface- or defect-related phenomena constitute a problem for their characterization using X-ray powder diffraction (XRPD), and Raman spectroscopy can provide useful complementary information. We have designed and realized a novel experimental set-up  [1] for simultaneous in situ Raman/<High-resolution XRPD> experiments, to take full advantage of the complementarities of the two techniques in investigating solid-state transformations at non-ambient conditions. The invaluable added value of the proposed experiment is the perfect synchronization of the two probes with the reaction coordinate and the elimination of possible bias caused by different sample holders and conditioning modes used in “in situ but separate” approaches. The set-up was developed by the Swiss-Norwegian Beamline at the European Synchrotron Radiation Facility in Grenoble and tested on  the photoinduced 2+2 cyclization of (E)-furylidenoxindole. In this experiment the surface-bulk complementarities of the Raman and XRPD probes were exploited. Raman allowed to detect the reaction speed at the surface in  the first step of the reactions, when no reaction is detected by XRPD. The complex polymorph space of the product phase (one stable and two metastable crystalline phase and one amorphous phase) was fully understood and the structure of one metastable phase was also solved.

[1] E. Boccaleri, F. Carniato, G. Croce, D. Viterbo, W. van Beek, H. Emerich and M. Milanesio, In situ simultaneous Raman/high-resolution X-ray powder diffraction study of transformations occurring in materials at non-ambient conditions, J. Appl. Cryst., 2007, 40, 684-693.

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