Study of the pseudopolymorphism in the host–guest systems
Аннотация
Supramolecular chemistry has opened a broad field of investigations to solid state physicists by its ability to produce new self-assembly materials [1]. A prototype tubular example of supramolecular self-organization is given by inclusion crystals, such as urea nanoporous compounds The host urea molecule forms hydrogen-bonded hexagonal channels of 5.5 diameter in which long guest chains like alkanes are densely packed in a one-dimensional arrangement. This simple paradigm crystal offers a unique opportunity to address at a fundamental level the question of the nature and the roles of interactions in self-organized architectures. Original physical properties in these host-guest materials are related to their aperiodic feature which, unambiguously, appears in their superspace diffraction pattern Here, we will present two quite new and unexpected results obtained in urea-alkane using neutron diffraction under Helium hydrostatic pressure: -the existence of a selective compressibility of the host and guest sublattice [4] -a total unexpected ordered phase where ordering does not require any apparent deformation of the host [5].