2(4)-Aminopyridines as Ligands in the Coordination and Extraction Chemistry of Platinum Metals

Abstract

The specific behavior of aromatic amines in the coordination and extraction processes of isolation and separation of platinum and other metals is discussed using the example of 2(4)-aminopyridines (2(4)-AP). As intrasphere ligands, 2(4)-AP have a high electron-donor capacity due to the pumping of an easily polarizable π-electron density. The chemistry of the extraction of platinum metals, iridium in particular, is considered: depending on the conditions, ion associates, coordination-solvated compounds or compounds containing an amine in the inner and outer coordination sphere of the metal are extracted. In the extraction of simple singly charged anions, there is a violation of the exchange-extraction series established for a large set of aliphatic amines. Soft anions (according to Pearson), for example, SCN- and I-, are best extracted, while for aliphatic amines such an anion is hard СlO4−. In the coordination compounds of platinum metals, 2(4)-AP acts as an electron donor, is coordinated by heterocyclic nitrogen with a redistribution of electron density not only to the accepting metal-complexing agent, but also further along the N-Me-X chain (X is an acido ligand in the composition of the complex), which leads to even greater covalence of the molecule as a whole.