Synthesis And Properties Of Coordinated Multiferroics With Croconic Acid And Rare Earth

In recent years, the inorganic-organic hybrid multiferroic materials gradually come into people’s sight. Owing to it possessing the advantages of inorganic multiferroic materials and organic multiferroic materials, it is a multi-functional material with bistable properties simultaneously in many channels, and more and more attentions are focused. The mechanism of ferroelectricity and magnetism is opposite, so one of the common strategies in synthetizing multiferroic material is adding magnetic elements into ferroelectric. Croconic acid, which has large spontaneous polarization at room temperature, is an organic ferroelectric, and it has been welcomed by many scientists since it was found to have ferroelectricity. On the other hand, with excellent photoeffect and magnetic effect, rare earth is ageless in the long journey of scientific research.In this research, croconic acid is employed as main ligand, and rare earth group as center cations in all complexes, and 2,5-pyridinedicarboxylic acid and alkali metal cation K+ are used as the second ligand/metal in order to adjust the polarity of crystal structures. Sixteen novel complexes have been obtained by means of volatile solvent and characterized by X-ray single crystal diffraction, infrared spectra, elemental analysis, ICP and powder diffraction. We studied their properties via thermogravimetric-differential thermal analysis, fluorescence spectrum, electric hysteresis loop and magnetic properties as while. The five main conclusions are given blow.1、Four new Tb3+ complexes (1-4) have been synthesized. Two of them crystallize in polar space group. Namely, complex 3 is a ternary complex containing the second ligand 2,5-pyridinedicarboxylate and complex 4 combines with the second metal K+. The other binary compounds 1 and 2 without the second ligand or cation crystallize in nonpolar space group. The results give us a hint that 2,5-pyridinedicarboxylic acid and alkali metal cation K+ may regulate the polarity of the system based on croconic acid and rare earth. Briefly, they can induce the generation of polar space group. Property determinations show that the four complexes can exist stably under 250 K and have characteristic emission peak on 530 nm, with an intensity order of complex 4>complex 3>complex 2 ≈complex 1. This result indicates that the second ligand 2,5-pyridinedicarboxylic acid and the second metal cation K+ can effectively improve the efficiency of fluorescence. Ferroelectric and magnetic measures of complex 4 display ferroelectric feature at room temperature and antiferromagnetic interaction between Tb(III) ions. Thus, complex 4 should be a potential multifunctional materials with optical, electric and magnetic properties.2、Four new complexes (5-8) have been synthesized with Dy3+ as center cation. Complexes 5 coupled with 6 crystallize in nonpolar space group and complexes 7 coupled with 8 crystallize in polar space group. The structures of complexes 5-7 are similar to complexes 1-3. Althoug the structure of complex 8 has none assistant ligand or metal cation, it is only obtained by adding K+ in the synthesis. This phenomenon demonstrates once more that 2,5-pyridinedicarboxylic acid and alkali metal cation K+ can regulate the polarity of the system. In additon, electric hysteresis loops at room temperature shows that complex 8 is a ferroelectric.3、Other rare earth elements were also studied. Complexes 9-12 and 14 have been synthesized with Pr3+, Er3+, and Lu3+, and crystallized in nonpolar space group. Complexes 13 and 15 have been obtained with Er3+ and Lu3+, and crystallized in polar space group when 2,5-pyridinedicarboxylic acid and alkali metal cation K+ are employed. The structures of complexes 13 and 15 are similar to complexes 3 and 8. Here, 2,5-pyridinedicarboxylic acid and alkali metal cation K+ seem easier regulate the polarity of the system based on medium and heavy rare earth. In addition, the complex 10 shows fluorescence emission spectrum at room temperature, so it is a potential luminescent material.4、A new complex (16) has been synthesized with Ag+ and croconic acid for the first time. It shows strong green emission at room temperature, which is relatively rare in silver complex.