Chemically Induced Spin-Crossover in an Iron(II) Bis(Pyrazol-1-yl)pyridine-Based Complex in Solution

Bis(pyrazol-1-yl)pyridine (1-BPP)-based iron(II) spin-crossover complexes have been widely investigated in the solid state. However, the application of such systems in the solution phase remains challenging. Here, we report a series of boronic acid-featured 1-BPP iron(II) complexes, one of which is capable of undergoing spin-state switching upon binding with acetate ions in solution. This finding enables us to develop spin-crossover molecular sensors for small anions.