Abstract
Variable temperature X-ray diffraction has been used to probe the structure and dynamics of the solid adducts of 1,3,5-trimethylbenzene (mesitylene) and hexafluorobenzene. PXRD patterns and DSC traces of near equimolar mixtures reveal two solid-state phase-transitions at 179.2 K and 111.0 K. The crystal structures of all three solid phases of this material have been solved by SXD. In contrast to previous studies on the adduct benzene–hexafluorobenzene, there is pairing of the mesitylene and hexafluorobenzene molecules in all three phases, each consisting of close-packed parallel columns of alternating C6H3(CH3)3 and C6F6 molecules packed face to face in a staggered conformation. Differences in structure between the phases illustrate the subtle interplay of quadrupole versus bond-dipole electrostatic interactions.
Highlights
Variable temperature X-ray diffraction has been used to probe the structure and dynamics of the solid adducts of 1,3,5trimethylbenzene and hexafluorobenzene
Powder X-ray diffraction (PXRD) patterns collected in 10 K intervals reveal the presence of three solid phases below the melting point[25] (Fig. 1 and S1‡)
In the PXRD patterns for the highest temperature phase I, the observed positions of the diffraction peaks are in good agreement with the unit cell and space-group symmetry determined by the pioneering 1970's single crystal diffraction (SXD) study,[10] Initially, indexing of the PXRD patterns of the intermediate phase II and the lowest temperature phase III were problematic due to some additional peaks with lower intensity
Summary
Variable temperature X-ray diffraction has been used to probe the structure and dynamics of the solid adducts of 1,3,5trimethylbenzene (mesitylene) and hexafluorobenzene. In the PXRD patterns for the highest temperature phase I, the observed positions of the diffraction peaks are in good agreement with the unit cell and space-group symmetry determined by the pioneering 1970's single crystal diffraction (SXD) study,[10] Initially, indexing of the PXRD patterns of the intermediate phase II and the lowest temperature phase III were problematic due to some additional peaks with lower intensity.
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