Synthesis And Characterization Of Acid-base Response Complexes Based On Acylhydrazone Ligand

Spin-cross complexes can achieve the transformation of spin state by regulating external factors,and are widely used in molecular sensors and molecular switches.The transition temperature of most spin-crossing complexes is far from room temperature,so they are not dominant in practical applications.Therefore,the design and development of multi-respponse spin-crossing materials that can be precisely controlled has become a new research focus and diffculty in recent years.In this dissertation,the Fe(II)complexes that can respond to acid-base are selected as the starting point to study the spin crossing phenomenon,and the spin-crossing behavior of complexes is adjusted p H to achieve the purpose of spin-change at room temperature.This paper is mainly divided into four chapters:The first chapter is the preface.It systematically introduces the research progress of spin-crossing complexes,inducing factors,and the development of Fe(II)complexes based on acylhydrazone ligands in spin-crossover.Finally,the topic selection ideas and research content of this thesis are described.In the second chapter,Fe(II)complexes Fe L₁(1)?Fe L₂(2)?Fe L₃·H₂O(3)based on acylhydrazone ligands HL₁-HL₃and their response to acid-base stimulation are studied.The keto and enol tautomerism of the acylhydrazone ligand occurs during coordination or protonation,so it may be used to synthesize a complex that responds to acid-base stimulation and can undergo a spin state transition near room temperature Things.Single crystal X-ray diffraction results show that complexes 1-3 are all single-core N₄O₂-type expected coordination structures.The magnetic susceptibility measurement indicates that the complex 1 is in a high-spin state in the entire test temperature range,and due to the combined effect of the substituents and the intramolecular interaction force,the complexes 2 and 3 are in the low-spin state.Various tests have confirmed that complex 1-3 can produce reversible response behavior to acid and base stimulation in solid phase and liquid phase.Under the action of acid,the complexes 2 and 3 will partially dissociate and cause the metal center to change from a low-spin state to a high-spin state.The base can restore the original coordination structure and magnetic behavior.However,high-spin solid-state coordination substance 1 does not change the spin state under the control of acid and base,but still has a reversible change of dissociation-recovery.In the third chapter,we report bidirectional spin-state switch and fluorescence modulation of an Fe(II)complex{[Fe(L)(HL)](Cl O₄)₃}·n H₂O(4),which based on a rhodamine B 2-pyridinecarbaldehyde hydrazone ligand in both solid state and solution.The complex is predominantly stabilized in low spin state at room temperature due to the strong ligand field strength imposed by acylhydrazone-pyridine.Heating to 400 K results in the change of the spin state to predominant high spin due to the loss of solvents and the desolvent sample shows reversible incomplete spin crossover in the following thermal cycles.Besides thermal-induced spin state change,acidification treatment of complex 4 results in iminol-amide tautomerization and dissociation of the complex,and hence the switch of the spin state to high spin at room temperature.Concurrent fluorescence enhancement was observed and was attributed to the intrinsic response of the rhodamine luminophore toward acid perturbation.The reverse switching is achieved upon further alkalization treatment.The fourth chapter is the summary and prospect of the above work.