Design of half-sandwich ruthenium complexes with dynamic porosity

Abstract

The main subject of this doctoral thesis is the realization of a new class of wheel-and-axle systems, designed on the basis of half-sandwich Ru(II) organometallic building blocks (WAAMO = wheel-and-axle-metallorganic). Our goal is to create a host unit that in the solid state, when exposed to an external stimulus, like gas or solvent vapors, is able to undergo a packing rearrangement in order to accommodate the guest molecules within its crystalline scaffold; moreover, this process should be completely reversible, i.e. the guest should be induced to leave the system (for example through an increase in temperature) by restoring the original structure without loss of crystallinity. In other words, we aim to generate flexible and dynamic networks with “pores on demand”, similar to the 3rd generation hosts described by Kitagawa for metal organic frameworks (MOF). Our complexes are constituted by two bulky half-sandwich Ru(II) metallorganic moieties [(arene)RuCl2] that are placed at the terminal ends of the molecule as wheels, and a linear spacer which may be built either by a ditopic bridging ligand or by supramolecular dimerization of the carboxylic functions present on properly chosen ligands. All the synthesized complexes have been characterized through IR and NMR spectroscopy, elementary and thermal analysis; finally they were structurally analysed by means of single crystal and powder X-ray diffraction. A particular interest was focused on the study of solvates, obtained both from solution synthesis and from crystallization experiments. The analysis of the structures allowed us to understand the influence of the guest presence on the resulting packing and led to the formulation of some hypothesis about the mechanism of conversion between the different crystal forms. Finally the solvation-desolvation processes of our systems were investigated and their reversibility was verified; in some cases guest-exchange experiments were performed and monitored through X-ray powder diffraction.