Synthesis And Characterization Of Cr-Ln Heterometallic Compounds Based On Polycarboxylate Ligands

Single-molecule magnets (SMMs) bear slow magnetic relaxation behavior under applied fileds and at low temperature, and have potential applications in the fields of quantum chemistry and high-density storage. A large number of 3d-4f SMMs have been synthesized recently, such as Mn-Ln、Cu-Ln、Co-Ln、Ni-Ln and so on. However, Cr-Ln compound is still rare due to the chemical inertness of Cr ion. Herein with the aim of synthesis of high-nuclearity oxygen-bridge Cr-Ln SMMs, some Cr-Ln compounds based on polycarboxylate ligands, such as 3-Nitrophthalic acid and Citric acid, were prepared and their magnetic properties were characterized.(1) The research progress of Cr-Ln heterometallic clusters were summarized based on the classification of ligands, providing basis of the choosement of ligands for the thesis.(2) With 3-Nitrophthalic acid(H2L) as ligand, three OD compounds [Ln4Cr4(μ3-OH)4(μ4-O)4(L)4(H2O)12]·(ClO4)4·3H2O·7DMF (Ln=Gd(1);Tb(2);Dy(3)) were synthesized. Structural analysis shows 1-3 are isomorphic, all bearing a metal skeleton with composition of three coplanar Cubic-type cages. Magnetic measurements indicate that 1 are antiferromagnetically coupled. Besides,3 displays slow relaxation of magnetization of SMM with Ueff is 10.82K and σ0is 2.97×10-5s respectively.(3) With Citric acid(H4cit) as ligand, three 3D compounds based on {Cr2Ln2(cit)6} and mononuclear Na+ were synthesized:Na12[Cr2Ln2(cit)6]·18H2O(Ln=Gd(4);Tb(5);Dy(6)), Structural analysis shows 4-6 are isomorphic. Secondly other three 3D compounds Na4Ca4[Cr2Gd2(cit)6(H2O)18]·10H2O(7);(H3O)6·Na2Ca2[Cr2Ln2(cit)6(H2O)12]·9H2O(Ln=Tb(8); Dy(9)) were synthesized by the reaction of 4-6 with CaCl2 respectively. Magnetic measurements indicate that 5 and 8 display slow relaxation of the magnetization, the Ueff and σ0 of 5 and 8 are 9.94K,6.71×10-5s and 12.69K,4.24×10-5s respectively. TGA analysis shows 7-9 have good thermal stability. TOPOS analyses indicates 6 has a (6,6)-connected pcu topology,7 has a (3,6)-connected rtl topology,8 and 9 have a (3,9)-connected new topology.(4) The assembly rules of the high-nuclearity oxygen-bridge Cr-Ln compounds were summarized.