| With the development of science and technology,the research on the molecule-based magnets has attracted more and more attention.The magnetic materials with bistability have been of intense interest due to their fundamental importance and unique potential applications in the light/heat switching and information storage devices.Molecular nanomagnet with slow magnetic relaxation behavior under low temperature,and spin-crossover complex with spin transition behavior near the room temperature are the most studied magnetic materials which display bistable magnetic states.With these in mind,in this dissertation,we focus on the syntheses and magneto-structural studies of new lanthanide-based SMMs and spin-crossover complexes with novel structures and functional properties.The main achievements of this work are listed as below:1.Pentanuclear lanthanide pyramids based on thiacalix[4]arene ligand exhibiting slow magnetic relaxationA series of pentanuclear Ln? clusters,[Ln5??4-OH???3-OH?4?L1??acac?6]?H4L1=p-teri-butylthiacalix[4]arene;acac = acetylacetonate;Ln = Dy,Ho,Er?and[Ln5??5-OH???3-OH?4?L1??L2?2?acac?2?CH3OH?2]?H3L2 = 5,11,17,23-tetrakis?1,1?dimethylethyl?-25,26,27-trihydroxy-28-methoxy thiacalix[4]arene;Ln = Dy,Ho,Er?,have been synthesized based on thiacalix[4]arene ligand.All of these complexes feature a square-based pyramid with four triangular Ln3 structural motifs.One ?4-OH group bridges four Ln? ions in the basal plane of 1-3,while the OH group in complexes 4-6 adopts ?5-coordination mode.Our results enrich the coordination modes of the versatile thiacalix[4]arene ligands and its application on new cluster compounds.Magnetic studies of all complexes reveal weak antiferromagnetic coupling among lanthanide metal ions.Among them,frequency dependent ?"?signals are observed for two Dys pyramids?1 and 4?,which may result from the presence of fast zero-field magnetic relaxation.2.Thiacalix[4]arene-supported heterodinuclear Ni?-Ln? complexes:slow magnetic relaxation behavior in dysprosium analogueThree heterodinuclear complexes,[?NiL4?Ln?L3??CH3OH?]·acetone?Ln = Gd?7?,Tb?8?,Dy?9?;H3L4 = 1,1,1-tris[?salicylideneamino?methyl]ethane?,were stepwise synthesized based on a thiacalix[4]arene ligand?H2L3?5,11,17,23-tetrakis?1,1-dimethylethyl?-25,27-dihydroxy-26,28-dimethoxy thiacalix-[4]-arene?.In 7-9,Ni? and Ln? ions are doubly bridged by two phenoxo 0 atoms of L4.The Ni? ion,only coordinated by the L4 ligand,features a {NiN3O3}coordination sphere;and Ln? ion adopts a seven-coordinated {LnO7} environment,capped by one thiacalix[4]arene ligand in a bowl-shaped conformation.Magnetic studies on all complexes reveal that ferromagnetic couplings are operative between the Ni? and Ln? ions.The dysprosium analogue?9?exhibits the field-induced single-molecule magnet?SMM?behavior under a dc-applied field of 800 Oe.Moreover,the Dy:Y?1:10?magnetically diluted sample?9'?shows slow magnetic relaxation at zero dc field.3.Solvent-induced change of magnetic properties in phthalocyanine supported dinuclear Ln? complexesThree dinuclear lanthanide complexes,[Ln2?thd?4Pc]· 2C6H6?Hthd =2,2,6,6-tetramethylheptanedione,Ln = Sm?10?,Tb?11?,Dy?12??,have been synthesized based on phthalocyanine?Pc?.They can be reversibly transformed into[Ln2?thd?4Pc]?Ln = Sm?10'?,Tb?11'?,Dy?12'??via desolvation and resolvation of the lattice benzene molecules.This change generates the dramatic influences on the structural and magnetic properties of the dysprosium analogue.In complex 12,one crystallographically independent metal center is observed,and it exhibits a single relaxation process of the magnetization with the energy barrier of 55.7 K.Upon desolvation,the resulted complex 12' contains two types of metal centers,and shows the field-induced single-molecule magnetic behavior with two thermally activated magnetic relaxation processes.The anisotropy barriers for 12' are as high as 63.3 K and 109.6 K,respectively.By desolvation and resolvation cycle of benzene solvent,a reversible change of the magnetic properties is successfully achieved.4.Modulating single-molecule magnetic behavior of a phthalocyanine supported dinuclear Er? complex by solvent exchange[Er2?thd?4Pc]·2C6H6?13?,obtained as green crystals from the reaction of[Er?thd?3]·2H2O with Lithium Phthalocyanine,Li2Pc,is a stable dinuclear complex with two Er? centers.Its lattice benzene solvent can be exchanged by soaking the crystals in dichloromethane to give[Er2?thd?4Pc]·2CH2Cl2?14?.The magnetic susceptibility data suggest different coupling interactions for the two complexes.While 13 exhibits fast relaxation and an estimated energy barrier of Ea = 2.6 cm-1 under 600 Oe dc field,the SMM behavior of 14 is field-induced and the energy barrier is higher at 34.3 cm-1.The source of this magnetic variation is probably related to disparate coupling interactions and subtle structural differences,as confirmed by ab-initio calculations.Importantly,the single molecule magnetic properties can be reversibly tuned through the exchange of solvent molecules,confirmed by further measurements on the reversed solvent complexes 13-re and 14-re.5.Modulating single-molecule magnetic behavior of a phthalocyanine supported Dy2 complex via bridging ligandTwo novel dinuclear dysprosium complexes,[Dy2?Pc?2?MeO-L5?2?H2O?]·2THF?15,MeO-HLs = 3-Methoxysalicylaldehyde?and[Dy2?Pc?2?EtO-L5?2?H2O?]·2THF?16,EtO-HLs =3-ethoxy-2-hydroxybenzaldehyde?,have been synthesized based on complex 12' and salicylaldehyde derivatives?RHL5?.15 and 16 are the similar mixed ligand triple-decker complexes,and both of them have two crystallographically independent Dy? ions,which two RL5 ligands coordinated between them.Each Dy?ions locates in {DyN4O4?coordination environment with four N donors from the outer Pc ligands and four O donors from the inner RL5 ligands or the coordinated water molecule.The magnetic susceptibility data suggest different coupling interactions for the two complexes.15 exhibits zero field single-molecule magntic behavior with two relaxation processes,which maybe attributed to two unequivalent metal centers.While the relaxation process of 16 is very fast under zero dc field due to the strong quantum tunneling effect.The source of this magnetic variation is probably related to disparate coupling interactions as confirmed by ab-initio calculations.The different coupling interactions is closely related to the subtle structural differences resulting from different spatial size and charge distribution of RL5 bridging ligand.6.Solvent sensitive Fe? complexe and correlations between spin crossover and fluorescenceOne novel complex[Fe?L6??L7?]·1.5?CH2Cl2??17·1.5CH2Cl2?were successfully synthesized based on[FeL6?MeOH?2]precursor and L7?1,1,2,2-tetrakis?4-?pyridin-4-yl?phenyl?-ethene?ligand.Complex 17·1.5CH2Clv2 shows a 4-fold interpenetrated two-dimentional structure,where the solvent molecules are stabilized in the crystal lattice through several non-classical hydrogen bonds.The magnetic susceptibility data of 17 and 17·1.5CH2Cl2 suggest that the solvent affect the SCO behavior observably.17 sows an incomplete SCO transition and T1/2=205 K.17·1.5CH2Cl2 shows a wide thermal hysteresis loop?24 K?.Interestingly,the SCO behavior of 17 can be finely tuned via changing the solvent molecules.Complex[Fe?L6??L7?]·3?CH3OH??17·3CH3OH?was obtained in methonal solvent,where the width of thermal hysteresis loop increases to 29 K.The most important is that the luminescent properties of the grafted fluorophores L7 can be adjusted by the spin states of 17 because of the synergetic effect between fluorescence and SCO. |
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