Virginie Niel

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

Abstract 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 π-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.

Cooperative thermal and optical switching of spin states in a new two-dimensional coordination polymer

(Fe(pmd)2[Cu(CN)2]2) (pmd = pyrimidine) displays a rigid two-dimensional structure and undergoes thermal- and optical-driven spin crossover behaviour; cooperative elastic coupling between iron(II) ions in the framework induces thermal hysteresis in the HS <--> LS conversion and sigmoidal HS --> LS relaxation of the photo-induced HS state at low temperatures.