Communication between iron(II) building blocks in cooperative spin transition phenomena

In the present article we discuss the cooperative nature of the spin crossover phenomenon in iron(II) complexes, providing a perspective of the state of the art in this area. The first aspect we discuss is the role of the intermolecular interactions, more precisely the pi-interactions, in mononuclear complexes. We show that by playing with the nature of the ligands, aliphatic, aromatic, or extended aromatic, it is possible to create stronger cohesive forces and receive a more cooperative response from the compound. In the next step the singular family of bipyrimidine-bridged iron(II) dinuclear compounds is presented as the simplest example of polynuclear spin crossover complexes exhibiting a rich variety of magnetic behaviours, which stem from the synergistic effect between intramolecular and cooperative intermolecular interactions. Finally, a number of polymeric 1-3D architectures of varying dimensionality and topology are discussed in terms of the search for strong cooperative spin crossover systems. (C) 2002 Elsevier Science B.V. All rights reserved.