Structural Insights into Hysteretic Spin‐Crossover in a Set of Iron(II)‐2,6‐bis(1<i>H</i>‐Pyrazol‐1‐yl)Pyridine) Complexes
Nithin Suryadevara, Asato Mizuno, Lea Spieker, Soma Salamon, Stephan Sleziona, André Maas, Erik Pollmann, Benoı̂t Heinrich, Marika Schleberger, Heiko Wende, Senthil Kumar Kuppusamy, Mario Ruben
Abstract
Abstract Bistable spin‐crossover (SCO) complexes that undergo abrupt and hysteretic (Δ T 1/2 ) spin‐state switching are desirable for molecule‐based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)‐2,6‐bis(1 H ‐pyrazol‐1‐yl)pyridine) (bpp) complexes – [Fe(bpp−COOEt) 2 ](X) 2 ⋅ CH 3 NO 2 (X=ClO 4 , 1 ; X=BF 4 , 2 ). Stable spin‐state switching – T 1/2 =288 K; Δ T 1/2 =62 K – is observed for 1 , whereas 2 undergoes above‐room‐temperature lattice‐solvent content‐dependent SCO – T 1/2 =331 K; Δ T 1/2 =43 K. Variable‐temperature single‐crystal X‐ray diffraction studies of the complexes revealed pronounced molecular reorganizations – from the Jahn‐Teller‐distorted HS state to the less distorted LS state – and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2 . Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule‐based switching and memory elements.