Syntheses, Crystal Structures And Magnetic Properties Of Lanthanide-carboxylate Coordination Compounds

Lanthanide-based molecular magnetic materials are currently of interest because of their potential applications in high-density information storage and quantum computing. Most lanthanide ions are good spin carriers with large ground state S values and have the large anisotropic moments resulted from the large spin-orbital coupling, which makes lanthanide-based coordination compounds displaying diverse magnetic behavior. However, rational design of the lanthanide-based magnets and regulation of the magnetic behavior of the lanthanid coordination compounds remains an exciting challenge.Seven novel lanthanide coordiantion compounds with the carboxylate organic ligands have been synthesized under hydro(solvo)thermal or ionothermal conditions.These coordination compounds are divided into three types of compounds according to the different organic ligands used.(a) Three chiral coordination compounds based on the chiral(S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid(HL1) ligand, namely,Ln2(μ2-L1)4(L1)2(phen)2(Ln = Dy(1),Gd(2), and Er(3); phen = 1,10-phenanthroline),have been presented.(b) Three coordination compounds({Ln4(μ3-OH)4(L2)8}n(Ln =Dy(4),Gd(5) and Er(6)) with the 2-(3-chlorophenoxy)propionic acid(HL2) ligand featuring tetranuclear Dy4(μ3-OH)4 cubane core units are obtained.(c) One three-dimensional compound, [{(EMIM)[Dy3(BDC)5]}n(7), obtained uner ionothermal reaction also synthesized in this thesis. All compounds have been characterized by X-ray single-crystal diffraction, IR spectra, elemental analyses, and thermogravimetric analyses. Additionally, some compounds are magnetically characterized in detail and the resuls show that the Dy-based compounds exhibit slow magnetic relaxation.This thesis contains five chapters.A brief introduction and the synthesis methods for the metal-organic coordination compounds are presented in the first chapter. Moreover, the latest research progress of the magnetic metal-organic coordination compounds is summarized in this chapter.The second chapter describes the synthesis and crystal structures of three chiral compounds Ln2(μ2-L1)4(L1)2(phen)2(Ln = Dy(1), Gd(2), and Er(3)) based on the(S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid(HL1) ligand. In these compounds two dysprosium ions are bridged by four carboxylate ligands to form the discretenoncentrosymmetric dinuclear Dy2 structures. The magnetic properties of these compounds have been investigated and the result show that a weak antiferromagnetic interaction between the Gd(III) ions are observed in the dinuclear structure. The Dy(1)analogue displays field-induced slow magnetic relaxation behaviour. However, no slow relaxation phenomenon was observed for the Er(3) derivative even in the presence of 2 k Oe applied field.Three compounds, namely, [Ln4(μ3-OH)4(L2)8]n(Ln = Dy(4), Gd(5) and Er(6)))with the 2-(3-chlorophenoxy)propionic acid(HL2) ligand have been syntheisized and crystal structural characterized, which is the topic of the third chapter. In these compounds four lanthanide ions are linked by four μ3-OH groups to give a tetranuclear cubic Ln4(μ3-OH)4 unit, which is further bridged by the carboxylate groups of the 2-(3-chlorophenoxy)propionic ligands to generate a one-dimensional chain. The magnet data of the compound Dy(4) show this compound display a slow magnetic relaxation in the absence of the applied field.Compound [{(EMIM)[Dy3(BDC)5]}n(7) with three-dimensional framework has been synthesized under ionothermal condition. Compound(7) is consist of the extraframework charge-balancing specie of imidazolium [EMIM]+ cation and the[Dy3(BDC)5]n–nanionic framework with hex topology. The 3D [Dy3(BDC)5]n–n framework is constructed from the 1D rod-shaped Dy-carboxylate secondary building unit inwhich the 6-, 8-, and 9-coordinated Dy(III) ions are alternately arranged.Detailed static and dynamic magnetic analysis of compound(7) revealed that compound 1 exhibits a field-induced slow magnetic relaxation behavior.The summary and outlook of the thesis are provided in the last chapter.