Oxamato/oxamidato-based multifunctional porous coordination polymers

Resumo

The main goal of this Ph.D. Thesis concerns the design and synthesis of multifunctional materials which is one of the most challenging topics for chemists and physicists working together in the multidisciplinary field of Materials Chemistry. In order to do so, we have taken advantage of the new developments of the metallosupramolecular chemistry, in particular the molecular-programmed self-assembly methods that exploit the coordination preferences of the metal ions and the versatility of the tailored ligands. In this sense, we have chosen functionalised oxamato and oxamidato derivatives to build extended architectures which can exhibit interesting features, the control of the porosity being one of them. Our efforts have been devoted to prepare porous coordination polymers (PCPs) and investigate the introduction of new physical properties such as chirality, gas sorption and separation or magnetic properties, among others. In this respect, two separated research lines have been explored whose results are shown in Parts 1 and 2. Part 1 deals with the development of a synthetic strategy to obtain chiral porous materials in an easy and effective manner. It consists of the functionalisation of enantiopure amino acids (alanine, valine, leucine and phenylglycine) whose encoded chiral information is efficiently transmitted to their derivatives and their different aliphatic residues play a non-negligible role in the self-assembling processes of the extended structures. In turn, Part 1 has been divided into Parts 1.A and 1.B, focusing on oxamato- and oxamidato-based compounds, respectively. Interestingly, both families of ligands gave rise to very different metalloligands and consequently, to a wide variety of fascinating chiral 3D frameworks which display interesting properties. In Part 1.A, we demonstrate that our metalloligand strategy represents an effective synthetic route to rationally prepare chiral PCPs, one of the unprecedented and striking result being the synthesis of a rod-like MOF from a preformed chiral 1D building unit. Among the oxamidato-derived PCPs shown in Part 1.B, we report a family of calcium(II)-derived PCPs which serves as an excellent platform to study how the gas sorption and selectivity can be tailored by tuning the electron density of the channels of the PCPs, thus achieving an easy manner to separate, for instance, methane from longer hydrocarbons in natural gas. Part 2 concerns the use of several post-synthetic methods (PSMs) to introduce new physical properties into preformed materials and thus to obtain multifunctional PCPs. In this chapter, we have explored three PSMs which are discussed in Parts 2.A, 2.B and 2.C. Taking advantage of the porous and anionic nature of the preformed PCPs and the resulting presence of counter-balancing cations within their 3D frameworks, we have performed the substitution of such cations and investigated the physical properties that the new materials show. In Part 2.A, we show how the exchange of the sodium(I) ions by lithium(I) and potassium(I) cations affords the derived PCPs which exhibit improved structural stability, gas sorption and magnetic properties. In Part 2.B, we are able to encapsulate a preformed iron(III) cationic complex within the pores of a PCP through cation exchange. This encapsulation results into interesting properties for both, the encapsulated complex and the original PCP. We go a step forward in Part 2.C and explore the substitution of not only the counter-balancing cations but also the metal ions constituting the coordination framework. Hence, we satisfactory exchange the diamagnetic magnesium(II) ions by paramagnetic cations from the first-transition row through transmetallation processes, affording two new magnetic materials which could not be prepared by direct synthesis.