Rotational disorder of bis(mesitylene)vanadium in channels of a triazine inclusion compound

Electron paramagnetic resonance (EPR) was applied to study rotational disorder of bis(mesitylene)vanadium (VBM, S = ½) in channels of 2,4,6-tris(4-Br-phenoxy)-1,3,5-triazine. To ensure a magnetically dilute system, decamethylbis(cyclopentadienyl)ruthenium was used as a main guest to fill the channels. X-ray diffraction confirmed inclusion formation, resulting in an incommensurate host–guest system. EPR spectra were measured using prismatic single crystals oriented to have Bo either parallel to the channel axis c or at any angle in between c and the perpendicular direction. Temperature-dependent spectra were recorded down to 80 K. The analysis revealed two types of paramagnetic guest entities, i.e. VBM (I) and VBM (II). Both showed dynamical effects due to a reorientational motion. VBM (I) is confined to show a molecular axis z distributed around c by a small angle (± 1.25°), whereas for VBM (II) the distribution is completely disordered. The reorientational motions are frozen at low temperature giving for VBM (II) a powder-like EPR spectrum. Analysing EPR intensities allowed us to conclude that the ratio of (I)/(II) species is of the order of 1.5.