Anomalous Spin Transition Observed in Bis(2,6‐bis(pyrazol‐3‐yl)pyridine)iron(<scp>II</scp>) Thiocyanate Dihydrate

Abstract

Abstract Bis(2,6‐bis(pyrazol‐3‐yl)pyridine)iron( II ) thiocyanate dihydrate undergoes a two‐step singlet ( 1 A 1 ) ⇄ quintet ( 5 T 2 ) transition in which both steps are associated with thermal hysteresis. Thermal cycling of the sample results in its conversion to a second phase which displays a single‐step transition with a very narrow hysteresis loop. This second phase slowly reverts to the initial phase on standing at 300 K. The interconversions are completely reversible. The spin state changes have been monitored by measurement of magnetism and Mössbauer spectra and by differential scanning calorimetry (DSC) studies.