Syntheses,Structures And Magnetism Of Some Bridged Complexes Based On Nitronyl Nitroxide

Molecular magnets have been of intense interest due to their potential applications as information storage,quantum computing devices and molecular spintronics.Molecular magnets of novel structures and interesting magnetic properties,including single-molecule magnets(SMMs),single-chain magnets(SCMs),high Tc magnets,photo-responsive magnets,spin-crossover(SCO)compounds and so on,have been prepared and reported.In the field of molecular magnets,nitronyl nitroxide radicals not only as act an excellent organic spin carrier,but could transfer the magnetic coupling,which have attracted the attention of numerous scientists all over the world.This thesis investigated the bridged transition metal or lanthanide single molecular magnets constructed by NIT-2-Pm or IM-2-Pm,in which 2-pyrimidinyl is a substituent group of Ullman type nitronyl nitroxide radical.The main results are as follows.First,we synthesized two unreported radical ligands 1(NIT-2-Pm)and its reduced radical 2(IM-2-Pm).Five new complexes have been synthesized and characterized structurally and magnetically,of which NIT-2-Pm or IM-2-Pm can be regarded as either a terminal or a bridging ligand depending on the synthetic conditions.Complexes 3 and 4 belong to mononuclear metal double spin system intead of exhibit single-molecular magnet behavior and just exhibit paramagnetic behavior.Compounds 5 and 6 are attribute to binuclear metals three spin system and do not show the frequency-dependent properties at zero field until at a 1 kOe dc field.Due to the isotropy of Mn?,the complex 5 just shows the field-induced frequency dependent behavior.Complex 6 is field-induced single-molecular magnet and the spin-reversal energy barrier is 13.5 K according to the Arrhenius law,indicating that the radical ligand can transfer the magnetic coupling effectively.Compound 7 displays characteristic paramagnetic behavior in the temperature range investigated since neither at zero field nor 1 kOe dc field can frequency-dependent propreties be observed.Four mononuclear lanthanide double spin system complexes have been synthesized and relevant magnetic properties have aslo been characterized.Similar to SMM behavior,all of them exhibit the frequency-dependent properties at zero field.However,no peak maxima are observed for ?m'' above 2 K.A static magnetic field was applied to suppress any possible quantum tunneling process(QTM).At a 1 kOe dc field or higher dc field,the in-phase susceptibility curves show no frequency dependent peaks.Based on that,six binuclear lanthanide three spin system complexes have also been synthesized.Ac magnetic susceptibility measurements were performed for 13-16 to probe dynamic magnetic behaviors.Under zero dc field,frequency dependence of the in-and out-of phase signal is observed for complex 14 alone.Complexes 13,15 and 16 display characterstic paramagnetic behaviors in the temperature investigated.Based on the above results,one unusual mixed 2p-3d-4f compound,of formula(?-NIT-2-Pm)Dy(hfac)3(H2O)Mn(hfac)2,exhibits the frequency-dependent property at zero field resembling SMM behavior.Its magnetic behavior is characteristic for antiferromagnetic interactions within the metal center and the coordinated free radical ligand.At last we got two samples of triradical compounds.Triradical 20 displays characterstic paramagnetic behavior in the temperature investigated.