Template burning effects on stability and boron coordination in boron levyne studied by in situ time resolved synchrotron powder diffraction

The thermal behaviour of a boron levyne containing quinuclidine was studied using in situ synchrotron X-ray powder-diffraction in the 25–900 °C temperature range. Rietveld refinements allowed to monitor the continuous transformations of the framework in real time providing information on the effects of the template removal on the framework geometry. Above 500 °C the dramatic change in the unit-cell parameters was related to the decomposition and expulsion of organic molecules. The structural deformation mechanism observed above this temperature was a cooperative tilting of the tetrahedra belonging to the double 6-membered ring accompanied by a simultaneous torsion along the [0 0 1] axis. The evolution of the bond distances and O–T1–O angles indicated the formation of trigonal boron in very good agreement with the NMR and FTIR analyses reported by Millini et al. (1992). A further framework deformation above 800 °C lead to a progressive lost of crystallinity defining the final thermal stability limit of the studied boron-substituted levyne.

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► In situ dehydration of [B4.4Si49.6O108]·6Q·18H2O was studied between 25 and 900 °C.
► Above 500 °C a cooperative tilting of the tetrahedra was accompanied by a torsion along the c-axis.
► Evolution of the T–O and O–T1–O angles indicated the formation of trigonal boron.
► Tetrahedral to trigonal boron conversion was related to template burning.