Spin crossover with thermal hysteresis in cobalt(ii) complexes and the importance of scan rate

Abstract

In this perspective article, firstly the handful of cobalt(II) complexes reported to date that show abrupt spin crossover (SCO) with thermal hysteresis is reviewed, focusing on the synthesis, structures and magnetic behaviour (which includes examples of multi-step SCO and of reverse-SCO). Secondly, the abrupt and hysteretic SCO complex [CoII(dpzca)2] is used as a simple case study to illustrate some of the effects of scan-rate on hysteresis loop shape, position and width. The key message is that, whilst often overlooked, kinetic considerations are important to SCO behaviour, so the mode (settle or sweep) and scan rate used for such studies should always be reported, ideally alongside a scan rate study of the hysteresis loop region, and relaxation rate studies within it.