Observation of proton-transfer-coupled spin transition by single-crystal neutron-diffraction measurement

Abstract

The application of single-crystal neutron diffraction (SCND) to observe proton-transfer phenomena in crystalline compounds exhibiting unusual protonation states or proton dynamics has garnered significant research interest in recent years. However,...

Development of an Iron(II) Complex Exhibiting Thermal- and Photoinduced Double Proton-Transfer-Coupled Spin Transition in a Short Hydrogen Bond

“…The Fe complex [Fe­(HL) 2 ] is the first to exhibit double PT coupled with spin crossover in a metal center. This behavior is in contrast to typical PCST complexes, in which intramolecular PT occurs in only one of the two ligands. − Spin crossover in a metal center from the HS to the LS state reduces the p K a of N Hyd , which is located in close proximity to the coordination sites in the ligands. This reduction in p K a is caused by the slightly increased level of electron donation from the ligands to the metal center with the geometric change around the metal center.…”

“…The occurrence of double PT is mainly attributed to the short HB, which reflects the small pK a difference between the hydrazone-N (N Hyd ) and phenol-O (O Phe ), indicating that PT can occur in response to subtle changes in pK a . 39,40 In this molecule, the positions of two protons can be controlled reversibly by temperature and photoirradiation in crystals as proton tautomerism, resulting in a distinct protonation state.…”