Structure:Function Relationships in Molecular Spin-Crossover Materials

A full understanding of cooperativity of a spin-transition requires detailed knowledge of structure of sample and of structural differences between different spin states. This chapter surveys the available structural data from different classes of complex, with a view to correlate cooperativity and structure changes associated with spin-crossover (SCO). The survey is necessarily incomplete, because structural data from spin-crossover compounds are often unavailable, or only available in one spin state. That is particularly true for the most cooperative materials where the large structure changes causing the cooperativity often lead to crystal decomposition during spin-crossover. None-the-less, enough structure: function data are available to allow some conclusions to be drawn. Examples of these cooperative materials discussed in the chapter include six-coordinate spin-crossover iron(II), iron(III), cobalt(II), and manganese(III) complexes. The chapter presents detailed discussions on molecular shape, crystal packing, and wide thermal hysteresis.