Over the past five years, the spin-crossover (SCO) phenomenon has experienced a clear new lease of interest from the scientific community coinciding with the recent publication of remarkable new advances. This perspective paper describes five illustrative examples of SCO systems, published during the past twelve months, showing new aspects of the unique and very appealing behaviour of these molecular switches, which may find interesting applications in the near future.

The two-step spin crossover of a new mononuclear iron(II) complex is studied by magnetic, crystallographic and calorimetric methods revealing two successive first-order phase transitions and an ordered intermediate phase built by the repetition of the unprecedented [HS–LS–LS] motif.