Solid State NMR Studies of n-Alkane/urea Inclusion Compounds

Abstract

The molecular characteristics of n-alkane chains in urea inclusion compounds are examined over a large temperature range (100 K to 300 K) using dynamic ²H NMR techniques. Particular emphasis is given to the guest properties in the vicinity of a solid-solid phase transition which is known to be accompanied by a distortion of the urea lattice. The analysis of the NMR data reveals several intra-and intermolecular motional processes which are responsible for spin relaxation in these systems. Likewise, it can be distinguished between confor-mational and overall chain order. Both the molecular dynamics and chain ordering are found to be strongly affected by the solid-solid phase transition. It is concluded that with respect to the guest components the phase transition can be assigned to a dynamic order-disorder transition.

Key Words:

• urea inclusion compounds
• ²H NMR spectroscopy