Studies On The Molecular Magnetic Materials Based On The Nitronyl Nitrioxide Radicals

Single-molecule magnets(SMMs)and single-chain magnets(SCMs)are of special interest and play a significant role in the development of molecular magnetism due to their potential applications in spintronic devices and quantum computers.Paramagnetic bridging ligands can significantly increase the magnetic coupling,especially for lanthanide ions,which is believed to be able to efficiently quench the quantum tunnelling of magnetization(QTM)process and to enhance the SMM properties.Due to their stability and easy chemical modification,the paramagnetic nitronyl nitroxide radical ligands(NIT-R)are widely used to construct diverse SMMs and SCMs.By adjusting the R groups,magnetic complexes with unique structures,topologies and magnetic properties are anticipated.This dissertation aims at the construction of NIT-R bridged SMMs and SCMs.Here,six radical ligands and their corresponding complexes were synthesized and characterized structurally and magnetically.The mainly results in this thesis are as following:1.Six radical ligands were synthesized:single radical ligands(NIT-py-Br,NIT-py-Cl,NIT-py-F)based on pyridine formaldehyde with different halogen atoms;a single radical ligand NIT-biph and a biradical ligand BiNIT-biph based on 4,4'-bipenyldicarboxaldehyde;a single radical ligand NIT-anti based on trans-Cinnamaldehyde.Except for compounds NIT-py-Br and BiNIT-biph,the other compounds are not previously reported.Single crystal structure analysis revealed the existence of?…?interactions in single radical compounds NIT-py-Cl,NIT-anti and NIT-biph.On the other hand,due to the steric hindrance of the four methyl groups in the biradical compound BiNIT-biph,no obvious?…?interaction between conjugated ring structure is noticed.According to the magnetic measurements,intermolecular antiferromagnetic exchange interactions were found in compounds NIT-py-Br,NIT-py-Cl,NIT-anti and intermolecular ferromagnetic exchange interaction in compound NIT-biph are noticed,while intramolecular antiferromagnetic radical-radical interaction was found in the biradical compound BiNIT-biph.2.To inversigate the possible influence of the different halogen atoms in the radicals on the structures and magnetic properties of the resulting metal complexes,a series of new transition metal and lanthanide metal complexes based on the radicals NIT-py-Br,NIT-py-Cl,NIT-py-F were synthesized.Unexpectedly,during the reaction processes with M(hfac)_n·2H₂O,the NIT ligands were reduced,resulting in the reduced radical IM(imino nitroxide)ligand-based complexes(Br-Co,Cl-Co,Cl-Ni,Cl-Mn)or non-radical derivatives(HIM)-based complexes(Br-Mn,Br-Tb,Br-Dy,Br-Ho,Br-Er,Br-Yb,Cl-Tb,Cl-Dy,Cl-Er,F-Dy).All these compounds are isolated complexes.Magnetic measurement revealed that complexes with transition metal ions and non-Kramers Ln^III ions didn't show any slow magnetic relaxation with or without the applied dc fields.On the other hand,complexes with Kramers Ln ^III ions(Br-Dy,Br-Er,Br-Yb,Cl-Er,Cl-Dy and F-Dy)show frequency-dependent ac magnetic susceptibilities under an applied dc field,indicating field-induced SMM behavior in these compounds.No obvious relationship between the halogen substituents and magnetism in these complexes were identified.For ligands NIT-biph and BiNIT-biph,no new metal complexes were obtained because of their weak coordination ability.3.Based on the ligand NIT-anti,three compounds with one-dimensional chain structure(anti-Cu,anti-Dy,anti-Tb)are obtained.The NIT-anti ligand serves as a bridging ligand to link two metal ions with the O-N-C-N-O groups in the trans position of the metal centres.Because of the steric effect of the hfac ions,?…?packing interactions are not observed between the chains.Magnetic measurements revealed the intramolecular ferromagnetic exchange interaction between the radical and metal ions in all compounds.Unfortunatelly,frequency-dependent ac magnetic susceptibilities were not observed either under a zero or an applied dc field in complexes anti-Dy and anti-Tb,which indicates the simple paramagnetic property of these one-dimensional compounds.