1H NMR Study of Molecular Motion of Benzene and n-Decane Confined in the Nanocavities of Metal–Organic Frameworks

Abstract

The molecular motion of benzene and n-decane confined in the nanocavities of [Zn4O(O2CC6H4CO2)3]n (IRMOF-1) was investigated in terms of the temperature dependence of the proton spin–lattice relaxation time (1H T1). Both substances exhibited two components of T1, below 216 K for benzene and 181 K for n-decane, indicating that the guest molecules are localized separately in large and small cavities. For n-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 n-decane and is associated with melting of the confined n-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 t...