Synthesis and characterization of multifunctional coordination networks: from structure to properties

This study presents the synthesis of new multifunctional materials, ranging from coordination polymers and metal-organic frameworks, to supramolecular peptide frameworks, and their structural investigation via X-ray diffraction techniques in order to correlate their structures to their properties. Eleven new compounds were synthesised while aiming to construct Hofmann-type networks, six of those exhibiting the expected topology. Their SCO properties were investigated, exhibiting a variety of different behaviours. AZO-1 and NICO-1 did not show SCO activity, staying in the HS state between 250 K - 100 K. In compound ISO-2, a crystallographic phase transition was detected upon cooling, although no change in the spin state was observed. BPA-2 exhibited a spin transition within the 200-290 K temperature range, being an interesting case of a SCO active material constructed with a flexible ligand though the topological control of a template ligand. Finally, the two isostructural PINA-1 and PINA-2 exhibited respectively an abrupt spin transition with 15 K hysteresis, and a gradual and incomplete transition with no hysteresis. The different SCO behaviours were attributed to the different amount of solvent present within the pores, which causes the transition to be incomplete. The porosity and host-guest properties of three other distinct materials were then investigated. The crystalline sponge method was used to attempt the incorporation of DASAs in the pores of the MOF material tptZn·xG, in order to explore the solid-state behaviour of their photoswitching mechanism. Despite the variety of conditions attempted, it was not possible to incorporate the DASA molecules into the network at sufficient levels for analysis via single crystal diffraction. Two new porous coordination polymers, compounds BDTC-1 and BDTC-2, were synthesised with lanthanoid ions and the flexible ppz-bdtc ligand, representing the first porous compound constructed with this ligand in which ppz-bdtc, as well as the framework, form in situ by self-assembly. Finally, a new crystalline supramolecular peptide framework with the capability to reversibly collapse and reinflate upon guest inclusion was constructed by self-assembly of a tetraproline helix in the polyproline II conformation.