2 research outputs found
<sup>1</sup>H NMR Study of Molecular Motion of Benzene and <i>n</i>-Decane Confined in the Nanocavities of Metal–Organic Frameworks
The molecular motion of benzene and <i>n</i>-decane confined in the nanocavities of [Zn<sub>4</sub>O(O<sub>2</sub>CC<sub>6</sub>H<sub>4</sub>CO<sub>2</sub>)<sub>3</sub>]<i><sub>n</sub></i> (IRMOF-1) was investigated in terms of the temperature dependence of the proton spin–lattice relaxation time (<sup>1</sup>H <i>T</i><sub>1</sub>). Both substances exhibited two components of <i>T</i><sub>1</sub>, below 216 K for benzene and 181 K for <i>n</i>-decane, indicating that the guest molecules are localized separately in large and small cavities. For <i>n</i>-decane below 181 K, methyl reorientation is excited although the rate of reorientation in large and small cavities differed, whereas the overall motion was frozen. A thermal anomaly accompanies the translational diffusion of <i>n</i>-decane and is associated with melting of the confined <i>n</i>-decane. For benzene, translational diffusion was also excited at the thermal anomaly at 216 K, indicating melting of benzene molecular assemblies in IRMOF-1. Below 216 K, the molecular motions in the large and small cavities differed. In the large cavities, benzene undergoes isotropic reorientation, which is unaffected by the thermal anomaly at 150 K, whereas in small cavities in-plane <i>C</i><sub>6</sub> reorientation occurs, and the isotropic reorientation and the intracavity diffusion are successively excited as the temperature increases. In particular, the acceleration of the isotropic reorientation of benzene accompanies the thermal anomaly at 150 K, corresponding to the partial melting of molecular assemblies in the small cavities
Structure and Dynamic Behavior of the Na–Crown Ether Complex in the Graphite Layers Studied by DFT and <sup>1</sup>H NMR
Diffusion
of alkali metals in graphite layers is significant for
the chemical and electrochemical properties of graphite intercalation
compounds (GICs). Crown ethers co-intercalate into graphite with alkali
metal (Na and K) cations and form ternary GICs. The structures and
molecular dynamics of 15-crown-5 and 18-crown-6 ether coordinating
to Na<sup>+</sup> or K<sup>+</sup> in GICs were investigated by DFT
calculations and <sup>1</sup>H solid state NMR analyses. DFT calculations
suggest a stacked structure of crown ether–metal complex with
some offset. <sup>1</sup>H NMR shows two kinds of molecular motions
at room temperature: isotropic rotation with molecular diffusion and
axial rotation with fluctuation of the axis. The structure and dynamics
of crown ether molecules in GIC galleries are strongly affected by
the geometry of the crown ether molecules and the strength of the
interaction between alkali metal and ligand molecules