This lecture explores the reactivity of pyridine complexes, focusing on the synthesis of pyridinium salts through reactions with Rx at high temperatures. The properties of these salts can be tuned to be hydrophilic or hydrophobic by modifying the functional groups or changing the anion. The process of anion exchange, illustrated with the example of silver iodide, is discussed, along with the driving force behind such transformations and the relevance of cations and anions in material properties.