The Self-assembly Of The Ln-TM Hetero Metals And Mixed Ligands

The design and construction of lanthanide-transition (Ln-TM)heterometallic compounds are of great popularity due to theirintriguing architectures and potential application in magnetism,luminescence, molecular sensors, ion-exchange and catalysis. Theheterocycle carboxylic acid ligands containing N donor have variouscoordination modes, and they are always potential hydrogen bondacceptors and donors. Therefore, it is a great synthetic strategy forthe construction of novel Ln-TM heterometallic compounds tointroduce these multidentate ligands. In this article, we chooseCo(Ⅱ), Ni(Ⅱ) and Ln(Ⅲ) cation as the metal centers, and choose2,3-pyridinedicarboxylic acid (H2pydc) and isonicotinic acid (HIN) as themultidentate ligands. Twelve Ln-TM heterometallic coordinationpolymers with three dimensional open framework structure havebeen obtained via adjusting the adding order and ratio of reactants,the time and temperature of reactions and the cooling rate underhydro(solvo)thermal conditions. All of them were characterized byinfrared spectroscopy (IR), X-ray powder diffraction andthermogravimetric analysis. The main work is summarized asfollows:1. Nine Ln-TM heterometallic complexes was synthesized by[LnCo(pydc)2IN(H2O)2]7H2O (Ln=Sm1, Eu2, Gd3, Dy4), [LnNi(pydc)2IN(H2O)2]7H2O (Ln=Eu5, Gd6, Tb7, Ho8),[LnNi(pydc)2IN(H2O)3]8H2O (Ln=La9). Same synthetic methods andreaction conditions can generate different products, which speakvolumes for the difficulty of accurate predictability of metal organicframeworks. It needs further researches to find the reasons causingthe different results.2. One Ln-TM heterometallic complexes was synthesized byusing H2pydc and HIN as ligands under hydrothermal conditions.Surprisingly, in situ reaction occurred and produced oxalic acid,which led to the generation of [LnCo(pydc)2(C2O4)0.5(H2O)3]·3H2O (Ln=Eu10). Hydro(solvo)thermal syntheses are often accompanied by insitu reactions, and generate unexpected products. However, it can yetbe regarded as a special way to prepare novel metal organicframeworks.3. Two isostructural Ln-Co heterometallic coordination polymerswere synthesized under solvothermal conditions by using H2pydcand HIN acid as multifunction ligand,[LnCo(pydc)2IN(H2O)2]·(CH3OH)·6H2O (Ln=Ho11, Yb12).4. The paper made a summary of the work, meanwhile, andrelevant conclusions were drawn.