Molecules with many spin-crossover sites could be used as multistepped molecular switches. The CNbridged molecular square [Fe II 4 (m-CN) 4 (bpy) 4 (tpa) 4 ](PF 6 ) 4 (bpy = 2,2'-bipyridine; tpa = tris(2-pyridylmethyl)amine), a Prussian blue analogue, undergoes thermally induced, two-step spin conversion. For more information, see the Communication by H. Oshio and co-workers on the following pages.

An iron(II) complex with ferrocenyl groups, [Fe(dppFc)2](BF4)2·2Et2O (1·2Et2O, dppFc = 1-ferrocenyl-2-{(2,6-bis(pyrazolyl)pyridyl}ethylene), was prepared. X-ray crystallographic analyses revealed that 1·2Et2O underwent a single-crystal-to-single-crystal transformation with the release of crystal solvent molecules. In magnetic susceptibility measurements, a reversible conversion between paramagnetism and spin-crossover induced by solvent molecules was observed.

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