Synthesis And Structure Of Alkaline-earth Complexes Based On Aromatic Carboxylate Ligands: From Monometal To Heterometal

The design and synthesis of new alkaline-earth metal complexes is an emerging area of interest owing to the potential applications of these complexes in various fields such as catalysis,materials,and biochemistry.However,most of the Previous works have been focused on complexes containing only one kind of alkaline-earth metals base on aromatic carboxylate ligands,while two-mixed-metallic complexes containing not only alkaline-earth metals but also other metals have seldom been explored,and these complexes fastened mainly on alkaline earth-transition metals systems.Compared with two-mixed-metal complexes,three-mixed-metal complexes based on alkaline-earth metals were even rare.A series of new alkaline-earth metal complexes(from monometal to heterometal) based on aromatic carboxylate ligands have been synthesized.These complexes were characterized by elemental analysis,infrared spectroscopic,thermal analysis,and X-ray crystallography,some thermochemical data were given.The main research contents and conclusions are summarized as follows:1)Complexes 1～7 based on 5-hydroxyisophthalate acid,5-nitroisophthalate acid and 2-pyrazinecarboxylate acid have been synthesized.The coordination numbers of Ca(Ⅱ)in complex 1 was 8,Sr(Ⅱ)in complexes 2 and 4 were 9,and Ba(Ⅱ)in complexes 3,5,6 and 7 were 9,9,9 and 10,separately,which revealed that the coordination numbers of alkaline-earth metal were in the sequence of Ca(Ⅱ)＜Sr(Ⅱ)＜Ba(Ⅱ);One types of metals were first chelated by heteroatoms and adjacent carboxylate groups oxygen atoms of heterocyclic carboxylate ligands,leaving the other uncoordinated oxygen atoms of carboxylate groups for the reaction with other kinds of metal salts,which provided the possibility for constructing the mixed-metal complexes.2)Two-mixed-metal complexes of 8-14 have been obtained by choosing pyridine-2,6-dicarboxylic acid ligand with suitable coordination capability,rigidity, sterically hindered and many coordination sites,when selecting lanthanide metal cations with appropriate Pauling electronegativities and coordination numbers. Investigation of the effect of pH in such complexes is of particular importance because it plays an important role in the crystal growth.3)Three-mixed-metal complexes of(Ae-Ln-A and Ae-Ln-Ae)15～21 were designed and synthesized under hydrothermal conditions,which revealed that metal cations of different hydroxide could also take part in coordination in the condition of higher pH;three different metals could be linked by pyridine-2,6-dicarboxylic acid ligands in three kinds of coordination modes.4)The data of thermochemical study enrich the physical chemistry about such alkaline-earth metal complexes.