Structure:function relationships in molecular spin-crossover complexes

Abstract

Spin-crossover compounds are becoming increasingly popular for device and sensor applications, and in soft materials, that make use of their switchable colour, paramagnetism and conductivity. The de novo design of new solid spin-crossover compounds with pre-defined switching properties is desirable for application purposes. This challenging problem of crystal engineering requires an understanding of how the temperature and cooperativity of a spin-transition are influenced by the structure of the bulk material. Towards that end, this critical review presents a survey of molecular spin-crossover compounds with good availability of crystallographic data. A picture is emerging that changes in molecular shape between the high- and low-spin states, and the ability of a lattice to accommodate such changes, can play an important role in determining the existence and the cooperativity of a thermal spin-transition in the solid state (198 references).

Four new spin-crossover salts of [Fe(3-bpp)2]2+ (3-bpp=2,6-bis[1H-pyrazol-3-yl]pyridine)

“…In any case, however, the absence of any direct hydrogen bonding or strong - interactions between the iron centres in 1 and 2, and the increased rigidity of their lattices induced by Ag...Ag or Au...Au bonding, are both consistent with the observed poorly cooperative spin-crossover [35]. The gradual spin-crossover behaviour of 4 is less surprising, given the encapsulation of each cation by the anions in the lattice (Fig.…”

A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes

“…The relationship between chemical structure and spin state is central to these phenomena 2, 11. A sterically crowded ligand sphere generally leads to high‐spin complexes 12.…”

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption

“…A possible approach to overcome this challenge consists of taking advantage of the sensitivity of spin-crossover complexes to subtle structural changes in metal coordination environments, which do not require magnetic cooperativity [13][14][15] . Thus, it has been shown that MOFs based on these molecular complexes exhibit magnetic switching at room temperature on physisorption of specific molecules within the porous framework 16,17 .…”