The sites and dynamics of p-xylene guest molecules in Dianin’s inclusion compound; a deuteron NMR study

Abstract

Abstraet. Single crystals of Dianin's inclusion eompound with methyl and ¡ deuterated p-xylene guest molecules were grown and studied by FT deuteron NMR. The spectra from the deuterated methyl groups reveal that these groups reo¡ rapidly down to 12 K; thereat~er they enter hato the tunneling regime. The rings of the p-xylene guests become motionless when T reaches 110 K. By measu¡ the orientation dependence of the quadrupole splittings, determining from these data the quadrupole eoupling tensors of the ring deuterons and relating these tensors to the C-D bond directions we infer the sites of the p-xylene guests in the cages of Dianin's inclusion compound. We final two sets of independent sites. Each contains three C 3 related individual sites. In each set the population of one of the sites is strongly depleted. The only large-angle molecular motions are 180 ~ rotational jumps about the long molecular axes. From measurements of T~ we conclude that these jumps are thermally activated, ro = 5.10 -~4 s, AE = 20 kJ/mol. Additional motions are rapid librations, also about the iong molecular axes. Their amplitude increases with increasing temperature, at 300 K it reaches 20 o. With 2D-exchange speetra we demonstrate that a p-xylene guest cannot change its site on a timescale of 100 ras anda tempe¡ expe¡ suggests that this is true on a timescale of several days even at T = 371 K.

Deuterium NMR studies of guest motions in urea inclusion compounds of 1,6-dibromohexane with analytical evaluation of spectra in the fast motion limit

“…The rotation angle of the alkane chain is quantified by the jump angle of the 13 deuterons, AO,, which is identical for both (3 deuterons. For deuterons 1 and 2, respectively, AO,(l) and O4a (2) give the angles between the C-D bonds from the initial gauche to the final orientation brought about by the rotation of the chain by AØ. Tetrahedral angles are assumed between all bonds.…”

“…His important work on clathrates [1][2][3][4][5] is but one example of his substantial impact on the field of nuclear magnetic resonance (NMR) spectroscopy of dynamic processes in solids. Here we present results on another host-guest system, the urea inclusion compounds.…”

Distance Measurements between13C Nuclei in Singly Labeledp-Xylene/Dianin's Inclusion Compound by 2D-RFDR

“…This is accomplished by inclusion of singly labeled p-xylene molecules at one of the methyl positions in the void cages of Dianin's compound. These methyl carbons do not experience any significant molecular motion (19). In this case we expect the value of T 2 ZQ to be large and, as will be shown, the experimental RFDR decay signals of the natural abundant host 13 C nuclei to provide nuclear distances.…”

Precision Measurement of the Quadrupole Coupling and Chemical Shift Tensors of the Deuterons in α-Calcium Formate

“…(7,28). It is built around a narrow-bore 11-T Bruker cryomagnet whose driftrate fell over the years well below the 10 −9 /h level, which is important for the present project.…”