Transition metals spin crossover phenomenon

The spin crossover phenomenon is known to take place in cubic coordination systems of transition metal compounds (TMC) with electronic configurations that may produce either HS or LS complexes, subject to the strength of the ligand field [24, 25]. For some values of the latter the two electronic configurations, HS... 

The thermally induced spin crossover phenomenon found in the solid state, as well as in solutions of the complexes of iron(II), iron(III) and cobalt(II), is a very promising, relatively new research field. In these complexes, the spin state of the central atom changes from high spin to low spin when the temperature is lowered. This phenomenon is expected to find application in the treatment of some tumors by hyperthermy. A transition metal complex is expected to be designed in such a way that its upper-limit transition temperature corresponds to the temperature desired for the treatment of some tumors by hyperthermy. It should be expected that the crossover phenomenon will attract a number of researchers. 

The spin crossover (SCO) phenomenon was studied extensively over the last 50 years (26). Compounds that exhibit a transition between the LS and HS states upon changes in temperature, pressure, or irradiation with light are attractive candidates for the development of magnetic sensors and memory devices (27). Most of the SCO compounds documented in the literature are Fe(II) complexes. An examination of the coordination environment of Fe(II) ions in many of these structures, includingthe very first Fe(II) SCO complex, [Fe (phen)2(NCS)2] (272), suggests that spin transition also can be observed in compounds where CN acts as a bridge between metal ions and is N bound to the Fe(II) center. 

Transition metal complexes of the 3d" type (n = 4, 5, 6, or 7), for which the spin state of the central metal atom changes from high-spin to low-spin when the temperature is lowered, constitute a phenomenon that has been much discussed lately.A review article of Giitlich et al. citing 192 references covers the field thoroughly until 1993. The phenomenon is accom-" panied by changes of magnetic and optical properties, which enable the so-called spin crossover (or spin transition) to be easily followed. 

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