Spin Crossover Properties Of Complexes Constructed From Pyridine-2,6-bis(Oxazoline)and Terpyridine Tridentate Ligands

Spin crossover compounds have received extensive attention due to their broad applications in molecular switch,information storage,and biosensing.This thesis mainly focuses on the structural modulation of pybox and terpyridine ligands,and attempts to introduce functional groups which aim to develop multifunctional spin crossover compounds.The detailed research includes the following aspects:1.Chirality induces structural symmetry changes and thus affects the spin transition behaviors.Meso and optically pure pybox ligands substituted with phenyl were exploited to construct meso(1),optically pure(2)and rac(3)[Fe(pybox)₂]²⁺complexes.The structures were obtained from X-ray single crystal structures and optimized ones via density functional theory(DFT)showed that the steric congestion between adjacent phenyl substituents caused the distortion of the coordination sphere of central Fe(?)ions.In three complexes,there is a distinct correlation between the midpoint temperatures of the SCO transition in solution and steric congestion of the structure.The greater the steric congestion,the lower the spin transformation temperature was observed.2.Complementary ligand pair strategy to construct hetero-ligand Co(?)SCO complexes.Inspired by the complementary pairing strategy of terpyridine in constructing complicated supramolecular systems,a family of heteroligand Co(?)complexes was synthesized from tranditional terpyridine(tpy)ligand and a clip tpy ligand modified with 2,6-dimethoxybenzene.The influence of the substituents on tpy on the SCO behavior of Co(?)complexes was discussed,and the fluorescent groups pyrene and triphenylamine were introduced into the ligands to construct multifunctional molecular materials.This strategy can also be used to develop multinuclear SCO compounds,and the obtained binuclear Co(?)complex contains an asymmetric thermal hysteresis loop with a width of 47 K.3.Halogen counterions tune the spin state of[Fe(pybox)₂]²⁺complexes.Pybox(or thio-pybox)ligands and different Fe(?)salts is used to synthesize a series of Fe(?)complexes with halogen as the counterions.Among them,1·2I₃ is a paramagnetic compound.There is a structural phase transition after annealing,and the saturation magnetic susceptibility increases after the phase transition.However,after annealing of the 1·I,whose complex solution has a shorter oxidation process in the air,exhibits abrupt transition with a thermal hysteresis loop of?T=27 K at 320-400 K.Up to date,the accurate structure of the compound has not yet been obtained.The substituents of the ligand and the flexibility of the five-membered ring can also significantly adjust the SCO activity.