Application of triple-channel 13C{1H,19F} NMR techniques to probe structural properties of disordered solids

Temperature-Dependent Structural Properties and Crystal Twinning in the Fluorocyclohexane/Thiourea Inclusion Compound

“…The re"ned isotropic displacement parameters for these guest atoms are large, clearly representing a smeared out (although nonuniform) time-averaged electron density distribution within the tunnel. Such structural disorder of the guest molecules is consistent with conclusions from solid state NMR studies (14,16,17). Figure 4 shows the single-crystal X-ray di!raction rotation photograph recorded for #uorocyclohexane/thiourea in the low-temperature phase (see Section 3).…”

“…Interestingly, the conformational properties of #uorocyclohexane (C H F) guest molecules in the thiourea tunnel structure (16,17) di!er signi"cantly from those of other monohalogenocyclohexane guest molecules (C H X, for X"Cl, Br, and I). For #uorocyclohexane, there are approximately equal amounts of guest molecules in the axial and equatorial conformations (16,17), whereas the other monohalogenocyclohexane guest molecules have a substantial excess of the axial conformation (12) (mole fraction in the range 0.85 to…”

The structural and dynamic properties of 1‐bromodecane in urea inclusion compounds investigated by solid‐state 1H, 13C and 2H NMR spectroscopy

“…head-to-head, tail-to-tail and head-to-tail [10,11] two resonances of the terminal groups reflect different terminal group arrangements. A previous report assigned the 13 C resonance of 1-fluorotetradecane/UICs, [48] similarly, it is concluded that the resonance at 15.6 ppm reflects CH 3 · · ·H 3 C end-group environment while the resonance at 15.3 ppm results from the CH 3 · · ·BrH 2 C endgroup environment. The intensity ratio of the two resonances is found to be 1 : 1, which indicates that for a given CH 3 (or CH 2 Br) group, there is an equal chance of having either CH 3 or CH 2 Br as a neighbour -neither alignment is more preferable over the other.…”

“…According to previous studies of UICs containing n-alkanes with a terminal functional group, [5,48] compared with the signals in solution. [5] Moreover, CH 2 Br carbon resonance shows a downfield shift of about 2.5 ppm, suggesting that 1-bromodecane in urea adopts an all-trans conformation while there is a mutual exchange between the gauche and trans conformation in solution.…”

Ring inversion of fluorocyclohexane in its solid thiourea inclusion compound

“…Furthermore, we have improved the 13C measurements by using triple-channel double-decoupling 13CÈM1H, 19FN spectra (both bandshape and selective polarization inversion) to increase both the resolution and temperature range of the 13C NMR experiments in comparison with the earlier work.2 A preliminary report of our 19F NMR study of the ÑuorocyclohexaneÈthiourea inclusion compound has been published. 15 Crystalline thiourea inclusion compounds16 are composed of an extensively hydrogen-bonded arrangement of thiourea molecules (the "hostÏ structure) in which there are uni-directional, non-intersecting tunnels. This host structure is stable only when it is Ðlled with suitable "guestÏ molecules, examples of which include branched hydrocarbons, cyclohexane and certain derivatives, and small organometallic molecules such as ferrocene.…”