Synthesis, Single-molecule Magnetic Behavior And Fluoescent Properties Of Lanthanide-organic Coordination Compounds

Metal-organic coordination compounds from metal ions with multifunctionalorganic ligands are currently of great interest due to their potential applications incatalysis, molecular magnets, photoluminescence, and gas adsorption. The research ofthe metal-organic coordination compounds is a hot topic in the filed of inorganicchemistry, physical chemistry, and material chemistry. Lanthanide coordinationcompounds are widely studied for their unique intrinsic optical and magneticproperties arising from4f electrons of the lanthanide centers. The significant magneticanisotropy arising from the strong spin-orbit coupling for lanthanide ions makeslathanide-based compounds highly promising systems that display diverse magneticproperties. The4f lanthanide ions usually exhibit a large ground-state spin and astrong easy-axis magnetic anisotropy that generates an energy barrier opposing thereversal of the magnetization, resulting in the slow magnetic relaxation behaviortypical of single-molecule magnets (SMMs). These molecular magnets can be viewedas potential candidates for spin electronics based on molecules and high-densityinformation storage devices.There are a variety of hydrothermal parameters such as reaction time,temperature, the chemical and physical properties of the reaction media, pH value,template, and molar ratio of reactants, and small changes in one or more of theparameters can have a profound influence on the final reaction outcome. The reportedmetal-organic coordination compounds are mostly obtained by the conventionalsolution synthesis, hydrothermal synthesis, and solvothermal synthesis methods.Recently there is a growing interest in using ionic liquids (ILs) as solvents forpreparation of crystalline metal-organic coordination compounds, which is a newsynthetic methodology developed-ionothermal synthesis. ILs comprising onlycompletely dissociated molecular cations (such as1-ethyl-3-methyl-imidazolium) andanions (such as halides) are a class of organic solvents. Deep-eutectic solvents (DESs)comprising mixtures of organic halide salts, such as choline chloride, with hydrogenbond donors, such as amides, amines, alcohols, and carboxylic acids are a class ofionic liquids. One advantage of DESs such as choline chloride/urea (or its derivatives) is their low cost, which makes DESs particularly desirable for applications in thelarge-scale synthesis of new functional materials. Urothermal synthesis is the usingthe urea or urea derivative as the solvent, which is another new synthesis method.New crystalline metal-organic coordination compounds with diverse physicalproperties and structures can be made via such unconventional synthesis methods,which are much different from those of synthesis methods in the conventionalsolvents such as water, ethanol, and N,N’-dimethylformamide.In the thesis, the ionothermal synthesis with the deep-eutectic mixtures as solventand the urothermal synthesis have been used for synthesizing a variety oflanthanide-organic oordination compounds. Ten lanthanide-organic coordinationcompounds with novel structures have been synthesized. The crystal structures of allcompounds have been determined by X-ray single-crystal diffraction. Some of thecompounds have been characterized by element analysis，powder X-ray diffractionpatterns (PXRD)，thermal analysis, and fluorescence spectra. Additionally, somecompounds are magnetically characterized. These ten compounds can be divided intothree groups based on the organic ligand used:(a) the first series of thelanthanide-organic coordination compounds based on the6-sulfonyl-1,4-naphthalenedicarboxylate (sndc) ligand,{[Ln(sndc)(e-urea)2](e-urea)}n(Ln=La(1) and Ce(2)), e-urea=ethyleneurea);(b) the second series of thelanthanide-organic coordination compounds with the2,2’-biphenyldicarboxylate(2,2’-bpdc) ligand,[Ln(bpdc)(NO3)(e-urea)3]n(Ln=Eu(3),Gd(4)and Tb(5)) and{[Ln4(bpdc)6(e-urea)2(H2O)2](e-urea)2}n(Ln=Dy(6) and Tb(7)) and (c) the thirdseries of the lanthanide-organic coordination compounds with the ethyleneurea(e-urea) ligand,[Ln(e-urea)8](NO3)3(Ln=Gd(8),Dy(9) and Tb(10)).The paper is divided into four parts:Chapter1: A brief introduction of metal-organic coordination compounds andlatest research progress of the metal-organic coordination compounds are presented.Chapter2: This chapter describes the synthesis and crystal structures ofcompounds {[Ln(sndc)(e-urea)2](e-urea)}n(Ln=La(1) and Ce(2)). Both compoundsexhibit a two-dimensional double-layered structure. The luminescent properties of thedoped with europium(III) based on the {[La(sndc)(e-urea)2](e-urea)}ncompounds arealso provided in this chapter.Chapter3: This chapter presents the synthesis and crystal structures of the fivecompounds,[Ln(bpdc)(NO3)(e-urea)3]n(Ln=Eu(3),Gd(4) and Tb(5)) and{[Ln4(bpdc)6(e-urea)2(H2O)2](e-urea)2}n(Ln=Dy(6) and Tb (7)). Compound [Ln(bpdc)(NO3)(e-urea)3]nhas a one-dimensional helical chain structure and thedetailed luminescent properties of Eu(3) and Tb(5) have been investigated. Compound{[Ln4(bpdc)6(e-urea)2(H2O)2](e-urea)2}nis also a one-dimensional chain structure butbased on the linear tetranuclear lanthanide cluster units. The magnetic properties ofthe {[Ln4(bpdc)6(e-urea)2(H2O)2](e-urea)2}nare studied in detail and the Dy(6)compound exhibits slow magnetic relaxation.Chapter4: Three compounds，[Ln(e-urea)8](NO3)3(Ln=Gd(8), Dy(9) and Tb(10)，have been synthesized and crystal structurally characterized in this part. Theseisomorphous compounds are discrete monoclear structures based on eight e-urealigands. The magnetic properties of Dy(9) and Tb(10) showed that the compoundDy(9) displays slow magnetic relaxation, which is the first example prepared from theurothermal synthetic method with a single ion magnetic behaviorChapter5: The summary and outlook of the thesis are proided in this chapter.