Polyfunctional Receptors for Ionic Species: Theoretical and Applicative Aspects.

The endless game of Cations and Anions, together with their coordination chemistries, is presented and broken down for the Reader into several levels. First, the de facto asymmetry existing between Cation and Anion Coordination Chemistry is introduced and explained from an historical point of view, undertaking a brief excursus from prehistory up to present-day. In second instance, concepts and tools of Supramolecular Chemistry are set forth, including Host-Guest Chemistry, mainly with metal cations in mind, and an overview of intermolecular forces, anion recognition being the focus. Lastly, core differences between Anions and Cations are discussed from a chemico-physical perspective building on the aforesaid supramolecular concepts. Experimental results and their interest are arranged following the natural distinction between oppositely charged species. On the Cations’ side applied research was conducted, focusing on the obtainment of Pd(II)-based green nanostructured heterogeneous catalysts for the Sonogashira cross-coupling reaction through a non-covalent approach. Ligands design, choice of the functionalization strategy and of the supporting substrate (MWCNTS) are illustrated in the light of the principles of Supramolecular Chemistry exposed in the introductory part. The material is organized hierarchically moving from the design, synthesis and characterization of isolated tectons up to the self-assembled working catalysts, passing for the study of the binary receptor-metal cation, receptor-MWCNTs and metal cation-MWCNTs systems. Beyond the promising results, other possible applications of the overall methodology are sketched out, with particular reference to the preparation of small (< 5 nm) supported Cu(0) nanoparticles. The Anionic section has a more basic research connotation, focusing on solution thermodynamics and solid-state structural features of the anion-π interaction. For this purpose, a new series of homologous ligands (L1-L4), featuring s-tetrazine as a binding site, was prepared. Protonation and structural features of the free ligands are pre-emptively presented and related to variations in their structures. Results of the study of their interactions with anions is broken down into four different paragraphs as follows: introductory investigation featuring inorganic anions, complexes of organic anions, the case-study of L2, forming adducts with the whole series of halide anions, and stabilization of polyiodide systems in the solid state through anion-π interactions, in view of their possible use as crystalline conductors. 21 crystal structures and about 100 determined equilibrium constants (shared between protonation and complex formation reactions) strongly support anion-π interaction as a valuable asset for the design of selective receptors for anions, shedding light on its interplay with different supramolecular forces and solvent effects beyond what can be summarized in these few lines.