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Pure Appl. Chem., 2008, Vol. 80, No. 6, pp. 1281-1292

Isoequilibrium relationships and cooperative effects in spin-state transitions in solution

Nader Hassan1, Andrei B. Koudriavtsev2 and Wolfgang Linert1

1 Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163-AC, A-1060 Vienna, Austria
2 Analytical Centre, D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia

Abstract: Thermal induced spin transitions between low- and high-spin states of Fe(II) complexes are commonly observed in the solid state. Cooperative effects, such as abrupt and two-step spin crossover, are typical for these objects and arise from intermolecular interactions described by several formalisms. These phenomena appear as deviations from the linearity of the respective van't Hoff plots. In solutions, molecular interactions manifest themselves in isoequilibrium relationships (IERs) as well as in a few cases of specific deviations of van't Hoff plots from linearity. The nature of these phenomena will be discussed on the basis of a statistical-thermodynamic model of spin crossover.