Thermal Behavior of Tetrahydropyran‐Intercalated VOPO 4 : Structural and Dynamics Study

The thermal behavior of tetrahydropyran‐(THP‐)intercalated VOPO 4 was probed by an extensive combination of experimental methods (XRD, DSC, FTIR, solid‐state NMR) and quantum chemical calculations. Two temperature‐induced transitions were detected and all polymorphs exhibit a high degree of molecular order and tight packing of THP in VOPO 4 . The first reversible thermal transition at around 100 °C was attributed to boat/chair conformation changes of the THP molecules. Most probably, a low‐temperature boat conformation of the guest molecules present in the interlayer space of VOPO 4 changes to a high‐temperature chair conformation. This rearrangement of the THP molecules was confirmed by variable‐temperature 13 C CP/MAS NMR spectroscopy. Quantum chemical calculations using a B3LYP functional and 6‐31G(d) basis set also support this idea. The second change at around 140 °C is probably caused by a weakening of the donor–acceptor bond between the oxygen molecule of THP and the vanadium atom of the host and the formation of a disorder in packing of the THP molecules. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)