Adaptive response of a metal-organic framework through reversible disorder-disorder transitions.

The ultrahigh porosity and varied functionalities of porous metal-organic frameworks make them excellent candidates for applications that range widely from gas storage and separation to catalysis and sensing. An interesting feature of some frameworks is the ability to open their pores to a specific guest, enabling highly selective separation. A prerequisite for this is bistability of the host structure, which enables the framework to breathe, that is, to switch between two stability minima in response to its environment. Here we describe a porous framework DUT-8(Ni)-which consists of nickel paddle wheel clusters and carboxylate linkers-that adopts a configurationally degenerate family of disordered states in the presence of specific guests. This disorder originates from the nonlinear linkers arranging the clusters in closed loops of different local symmetries that in turn propagate as complex tilings. Solvent exchange stimulates the formation of distinct disordered frameworks, as demonstrated by high-resolution transmission electron microscopy and diffraction techniques. Guest exchange was shown to stimulate repeatable switching transitions between distinct disorder states.

Structure solution with automated electron diffraction tomography data: different instrumental approaches.

Over the past few years automated electron diffraction tomography has become an established technique for structure solution of nano-crystalline material. The intentional choice of an arbitrary tilt axis and thus, the use of nonoriented diffraction patterns (off-zone acquisition) together with fine equidistant sampling of the reciprocal space result in high quality intensity data sets. Coupling automated electron diffraction tomography with electron beam precession (Vincent & Midgley, 1994) enables sampling of intensities between the static slices of reciprocal space and therefore enhances the quality of intensity data further; relatively complex structures have been solved using 3D electron diffraction intensities extracted from automated electron diffraction tomography data. Automated electron diffraction tomography data was collected initially using a dedicated automated module. In this manuscript we demonstrate that electron diffraction data of comparable quality can be collected using manual technique that mimics the automated process. A rather difficult material, i.e. a low symmetric (triclinic) sodium tetratungstate (Na(2) W(4) O(13) ) including heavy and light scatterers, was selected for testing. In this paper we show, that all collected data sets - automatic and manual, with and without electron beam precession - were able to provide data slightly different but suitable for ab initio structure solution and refinement.