Low-dimensional Carboxylate-based Coordination Complexes:Syntheses,Structures,and Magnetic Studies

As a rapidly developing research field,molecular based magnetic materials are mainly used to design and research new electronic and magnetic devices with adjustable properties.Compared with traditional solid materials,molecular magnetic materials have the advantages of light weight,solubility,versatility,and so on.Low dimensional metal complexes have attracted much attention from both physical and chemical perspectives due to their beautiful and complex structures and interesting physical properties,especially molecular magnetism.The choice of ligands is very important to obtain the complexes with expected structures.Carboxylate ligands have a variety of coordination modes:mono-or bis-chelate fashion,μ²-η:η,bridging mode,and so on,which are conducive to the structural diversity of the target complexes.Therefore,using 4-methyl-3-nitrobenzoic acid（HL）as ligand,we have successfully obtained five low dimensional complexes with transition metals and lanthanidemetals,Co^ⅡL₂（CH₃OH）₄（1）,Ni^ⅡL₂（CH₃OH）₄（2）,[Fe₆^ⅢL₁₂（CH₃OH）₄（H₂O）（OH）（μ₃-O）₂]·Cl·7H₂O·3CH₃OH（3）,{Gd₃^ⅢL₉（H₂O）₃（CH₃OH）₃}_n（4）,and{Dy₃^ⅢL₉（H₂O）₃（CH₃OH）₃}_n（5）,respectively.We studied the structures and magnetic properties of compounds 1-5.The details are as follows:（1）We have successfully prepared three zero dimensional clusters by slow solvent evaporation at room temperature,Co^ⅡL₂（CH₃OH）₄（1）,Ni^ⅡL₂（CH₃OH）₄（2）,and[Fe₆^ⅢL₁₂（CH₃OH）₄（H₂O）（OH）（μ₃-O）₂]·Cl·7H₂O·3CH₃OH)（3）.In complexes 1and 2,the COO^-groups coordinate with metal centers in a mono-chelate fashion,thus forming mononuclear clusters.Theμ₂-η¹:η¹ COO^-anions in compound 3 connect Fe^Ⅲthrough an end-to-end mode,obtaining a cyclic cluster.Magnetic studies show that antiferromagnetic interaction exists in compound 3.Compound 3 is composed of triangles[Fe₃^Ⅲ（μ₃-O）]⁷⁺cations and exhibits spin frustration with ground state spin S_T=1/2.（2）By solvothermal method,two new low dimensional carboxylate complexes were successfully prepared,Gd₃L₉（H₂O）₃（CH₃OH）₃（4）and Dy₃L₉（H₂O）₃（CH₃OH）₃（5）.In compounds 4 and 5,the COO^-groups alternatively linked Gd^Ⅲ/Dy^Ⅲ to form one-dimensional chains by using theμ₂-η¹:η¹ mode.The magnetic studies show that there is antiferromagnetic interaction in compound 5.