Synthesis And Characterization Of Cr-4f Heterometallic Cluster Materials

Polynuclear metal clusters have drawn lots of attentions in inorganic chemistry, not only because of their various numbers and intriguing structures, but also excellent magnetic properties, such as the slow relaxation of the magnetization and the magnetocaloric effect (MCE), which may have potential applications in information storage and processing, ultra low-temperature refrigeration. Up to now most of the magnetic research is focused on focused transition metal clusters or3d-4f heterometallic clusters, such as Mn-Ln, Co-Ln, Cu-Ln, Ni-Ln. compounds. In contrast, polynuclear Cr-Ln heterometallic clusters and poly-dimensional compounds containing3d-4f cluster units are very rare. Therefore, in this thesis new poly-dimensional compounds containing Cr-Ln cluster units were designed and synthesized. Their magnetic properties were investigated.(1) With maleic acid as ligand, three2D coordination polymers based on{Na2Cr2Ln3} and mononuclear Na+ion nodes were synthesized:{[Na(H20)][Na2Cr2Ln3(u3-OH)6(maleato)6(H2O)i7]}·nH2O (Ln=Gd, n=19(1); Tb, n=16(2); Dy, n=15.5(3)). Structural analysis shows that compounds1-3are isomorphic and have a (6,3) honeycomb structure. The2p-3d-4f unit features a bicapped trigonal bipyramidal{NaiCr2Ln3} metal skeleton. Magnetic measurements reveal that compounds1-3have ferromagnetic interactions, while2and3also show relaxation of the magnetization.(2) With sulfate as ligand, three3D (6,6)-connected frameworks based on{Cr2Ln4} units with pcu topology were synthesized:[Cr2Ln4((μ4-O)2(μ3-OH)4(H2O)9(SO4)5]-nH2O (Ln=Gd, n=3(4); Tb, n=2.5(5); Dy, n=1(6)). Structural analysis shows that the{Cr2Ln4} unit has a face-shared, double cubane metal skeleton. Magnetic analysis shows that4and5have obvious antiferromagnetic interaction and6bears ferromagnetic interaction. Besides,4has a moderate magnetocaloric effect,5and6display slow relaxation of the magnetization, and6exhibits single relaxation process.(3) With1,3-diamino-2-hydroxy-propane-N, N, N’, N’-tetraacetic acid (Hshdpta) as ligand, a3D (4,4)-connected coordination polymer based on [Cr2(hdpta)(CH3COO)2]-and mononuclear Na+ion nodes were synthesized:Na[Cr2(hdpta)(CH3COO)2](7). Further reaction of7with Gd(NO3)3leads to a ID chain based on [Cr4(hdpta)2(OH)4]2" and [Gd(H2O)5]3+units:[Gd(NO3)3(H2O)4][Cr4Gd(hdpta)2(OH)4(H2O)5]-NO3-67H2O (8). The magnetic studies reveal that8shows overall antiferromagnetic interactions. (4) The assembly rules of the multi-dimensional compounds containing Cr-Ln clusters were summarized.