Synthesis,Structures And Properties Of Linear 3d/4f Functional Coordination Compounds

The research on design, synthesis and magnetic properties of polynuclear clusters of paramagnetic metal ions has long been a focus of coordination chemists due to potential applications. In this thesis, nine new compounds have been synthesized by the reactions of polydentate salicylaldehyde ligands with transition metallic and lanthanides ions.All compounds were characterized by elemental analysis, IR, X-ray diffraction, fluorescence spectra as well as direct current and alternating current magnetic susceptibility measurements. The works are listed as follows:1. Ln₂Mn?_C7H₅O₂?₈ ?Ln= Gd ?1?, Tb ?2?, Dy ?3?, Ho ?4? and Er ?5?? family:Three metal ions are connected by six ?2-phenolate oxygen atoms of six salicylic aldehyde ligands, resulting in perfect linear [Ln?-Mn?-Ln?] structures. Magnetic studies of these complexes have been performed and AC susceptibility measurements show the presence of temperature-dependent out-of-phase ac signal for complexes 2 and 3 indicating single-molecule magnets ?SMMs? behavior. The Dy?2Mn? compound shows double relaxation pathways which may originate from the single ion behavior of individual Dy? ions and the weak coupling between Dy? and Mn? ions, respectively. The Ueff of 92.4?2? K is a relatively high value among 3d-4f SMMs. Moreover, complexes 2 and 3 represent the first linear Mn-Ln SMMs containing only divalent manganese ion as far as we know. The result suggests the positive effects of magnetic coupling to enhance their SMM behavior, presenting a promising strategy for constructing efficient heterometallic SMMs.2. The synthesis, structural characterization and magnetic properties of four related heterometallic complexes with formulas [Dy?2Co??_C7H₅O₂?₈]·6H2O ?6?, [Dy?2Ni??_C7H₅O₂?₈]·?C7H6O2?2 ?7?, Tb?2Con?_C7H₅O₂?₈ ?8?, and Dy?2Cd??_C7H₅O₂?₈ ?9? were reported. Each of complexes has a perfectly linear arrangement of the metal ions with two terminal Ln??Ln?= Dy?, Tb?? ions and one central Mn ?M?= Co?, Ni?, Cd?? ion. It was found that 6-8 displayed obvious magnetic interactions between the spin carriers according to the direct current ?dc? susceptibility measurements. Alternating current ?ac? magnetic susceptibility measurements indicate that complexes 6-9 all exhibit single-molecule magnet ?SMM? behavior while the replacement of the diamagnetic Cd11 by paramagnetic ions leads to a significant slowing down of the relaxation thanks to the magnetic interactions between 3d and 4f ions, resulting in higher relaxation barrier for complexes 6 and 7. Moreover, both Dy2Co and Dy2Ni compounds exhibit dual relaxation pathways which may originate from the single ion behavior of individual Dy? ions and the coupling between Dy? and Co?/Ni? ions, respectively, that can be taken as the feature of 3d-4f SMMs. The Ueff for 6 of 127 K is a relatively high value among the reported 3d-4f SMMs. The results demonstrate that the magnetic coupling between 3d and 4f ions is crucial to optimize SMM parameters. The synthetic approach illustrated in this work represents a promising route to design nd-4f based SMMs via incorporating suitable paramagnetic 3d even 4d and 5d ions into d-f system.