Synthesis,Structures And Properties Of Rare Earth Complexes Based On Carboxylates

The carboxylate ligands have been used to construct a variety of functional complexes because of their strong coordination capability and great variety of binding modes. Among them rare earth complexes with carboxylate ligands is the most important. Due to the extensive applications in magnetism, photoluminescence, catalysis, and other advanced functional materials, the rational design and synthesis of rare earth complexes with carboxylate ligands has become a hot spot of the current research. The introduction of chirality into rare earth complexes with carboxylate ligands can expand their function, and leading them to be an important research field in multifunctional materials of rare earth complexes. Interest in magnetic refrigeration has mushroomed in recent years for its advantage, such as environment friendly and high refrigerant capacity. Among them, GdIII-based complexes are regarded as promising candidate materials for magnetic refrigerators, because of the large-spin ground state(S), negligible magnetic anisotropy(D = 0), and weak exchange interaction of GdIII ion. In this thesis, we report fourteen new rare earth complexes with carboxylate ligands derived from three primary ligands, including R-2-phenylbutyric acid, 2-thiophenecarboxylic acid and iminodiacetic acid. These complexes are synthesized under diffused or hydrothermal condition, followed by structural and performance. The main contents are summarized as follows:1. Study on synthesis and properties of rare earth complexes derived from chiral carboxylate ligands is introduced. Twelve chiral dinuclear lanthanide complexes [Ln(R-PBA)3(phen)]2(Ln = La(1)、Ce(2)、Pr(3)、Nd(4)、Sm(5)、Eu(6)、Gd(7)、Tb(8)、Dy(9)、Ho(10)、Er(11)、Yb(12) have been synthesized by using(R)-2-phenylbutyric acid(R-PBA) as primary ligand, 1,10-phenanthroline(phen) as subsidiary ligand and lanthanide chlorates as rare earth ion sources by liquid/liquid diffusion. The single X-ray crystallography studies revealed that complexes 1–10 are isostructural and crystallize in the chiral space group P21. Moreover, their enantiomers [Ln(S-PBA)3(phen)]2 were obtained in the same way, and their chirality were further confirmed by the CD spectra. The photoluminescent measurements showed the photoluminescence of complexes 6, 8 and 9 in CHCl3 solution are typical narrow emission bands of their lanthanide cations. Magnetic investigations on complexes 7–11 revealed that 7 and 11 exhibit ferromagnetic couplings between the two LnIII ions, while antiferromagnetic couplings between the two LnIII ions exist in 8–10. And the alternating current magnetic susceptibilities of complexes 9 showed that it does’ t exhibit slow magnetic relaxation behavior.2. Study on the synthesis and properties of GdIII-based magnetic refrigerants is presented. A dinuclear GdIII-based complexes [Gd(2-TCA)3(phen)]2·H2O(13) was obtianed by employing 2-thiophenecarboxylic acid(2-TCA), 1,10-phenanthroline(phen) and Gd2O3 under hydrothermal reactions, and the CrIII-GdIII complexes [Gd Cr(IDA)2(C2O4)]n(14) was synthesized by using iminodiacetic acid(IDA), Cr O3 and Gd2O3 under hydrothermal condition. Structural determination revealed that 13 is a single-molecule compelex and crystallizes in the space group P1_, while 14 is a 3D coordination polymer with two-fold interpenetrating structrue and crystallizes in the space group P42/mbc. The magnetic properties have been investigated and revealed that both two complexes exhibit antiferromagnetic couplings between the metal ions. And complexes 14 showed relatively large magnetocaloric effect, having potential application for ultralow-temperature refrigeration.