A Reversible Hydrogen-Bond Isomerization Triggered by an Abrupt Spin Crossover near Room Temperature

The spin crossover salt [Fe(bpp)(2)](isonicNO)(2). 2.4 H2O (1.2.4 H2O) (bpp=2,6-bis(pyrazol-3-yl)pyridine; isonicNO=isonicotinate N-oxide anion) exhibits a very abrupt spin crossover at T-1/2=274.4 K. This triggers a supramolecular linkage (H-bond) isomerization that responds reversibly towards light irradiation or temperature change. Isotopic effects in the thermomagnetic behavior reveal the importance of hydrogen bonds in defining the magnetic state. Further, the title compound can be reversibly dehydrated to afford 1, a material that also exhibits spin crossover coupled to H-bond isomerization, leading to strong kinetic effects in the thermomagnetic properties.

Automated summary

The spin crossover salt [Fe(bpp)(2)](isonicNO)(2). 2.4 H2O undergoes a very abrupt spin crossover at 274.4 K, with reversible response to light irradiation or temperature change; Isotopic effects in the thermomagnetic behavior highlight the significance of hydrogen bonds in determining the magnetic state; The compound can be reversibly dehydrated to produce 1, which also exhibits spin crossover coupled with H-bond isomerization, resulting in strong kinetic effects in the thermomagnetic properties.