Supramolecular Magnetic Materials

Abstract

The incorporation of localized unpaired electrons into molecules and molecular materials provides the basis for a wealth of fascinating and rapidly developing science. Beyond an interest in the intrinsic properties of systems with localized spins (i.e. relating to attributes such as colour, magnetic moment, and chemical reactivity) comes a diverse range of magnetic and electronic phenomena in which transitions can be induced between different spin and spin-ordered states, with dramatic resulting changes in properties observed. Such phenomena perhaps most notably span the field of molecular magnets, in which the unpaired spins align with respect to each other through exchange-coupled pathways to give a rich array of spin-ordered ground states, and the field of spin-crossover, in which transition metal centres may be switched between alternate spin states in response to stimuli such as temperature, pressure, and light irradiation. Of further interest under this broad umbrella are properties such as valence tautomerism, in which spin-switching is achieved through metalligand intervalence charge transfer, and mixed-valency, in which differing oxidation states (commonly involving unpaired spins) may exist within the one system, including with varying degrees of delocalization. A unifying feature of all of these phenomena, other than that they involve unpaired electrons, is that they depend intimately on various types of communication between the electronic spins, each of which are subject to considerable variation through molecular, supramolecular, and materials design. Accordingly, a particularly intriguing aspect of this science – one that is in abundant display in the contributions that make up this Research Front – is the highly complex nature of the links between structure and resulting function for these systems. This complexity makes advances in this area dependent on a multidisciplinary approach in which new molecules and materials are synthesized, their structures and properties determined, relationships between these gleaned, and, subsequently, new systems are designed and synthesized, subject to the considerable whims of molecular selfassembly. Driving these efforts are a fascination with the endless complexity of this chemistry and, increasingly, the desire to