Spin crossover in iron(II)-containing complex compounds under pressure

The spin crossover phenomenon consists in the switching between two spin states of the central ion in 3d transition metal molecular complexes. The paper crossover can be induced and controlled by temperature, pressure, light radiation etc. The paper reviews all aspects of hydrostatic pressure influence on spin-crossover properties of iron(II) complex compounds. The applied hydrostatic pressure make it possible to influence the crystal lattice, revealing the role of elastic fields in the cooperative interaction of spin-crossover complexes, and to change directly the volume characteristics of complex molecules, the distances between the central ion and ligand atoms, and thus to have effect on crystal field strength. The experimental results for all types of iron(II) containing spin-crossover structures are discussed in details, and the theoretical consideration of the observed effects is given. The physical principles of the molecular spin crossover are adequately described by the ligand field theory while the macroscopic properties are under-stood on the basis of electron-phonon coupling and elastic properties of the crystal lattice.