Syntheses, Structures And Performances Of Rare-earth Coordination Polymers With Carboxyl Ligands

Recently, the construction of coordination polymers with carboxyl ligands has been a field of rapid growth not only for their intriguing architectures and topologies but also for their applications in areas of catalysis, sorption, separation, luminescence, magnetism, nonlinear optical property etc., In particular, rare-earth carboxylates coordination polymers have been of more great interests due to: (1) the atoms of rare-earth elements can act as hard acids being strongly coordinated by oxygen atoms behaved as hard bases. (2) The rare-earth elements possessing high coordination numbers and variable coordination geometry might be fruitfully utilized to generate interesting topological nets. (3) The 4f obitals being very efficiently shielded by the fully occupied 5s and 5p oribitals may give unique properties. In this paper, different reaction systems have been selected to synthesize four series of coordination polymers in order to study on the effect factors influencing the structure of the coordination polymers, such as solvent, pH and temperature etc. of the final products at hydrothermal conditions. The assembly reactions of ligands containing carboxyl and rare earth elements have yielded 20 coordination polymers. The IR, UV-Vis-NIR, XRD, TG-DTA, fluorescence spectra and magnetism have also been studied, which would take an important role in the explorations of structures and functions for coordination polymers.1. Five rare earth coordination polymers with citric acid, [Ln(Hcit)(H2O)]n (Ln = Ce(1), Pr(2), Sm(3), Dy(4) and Er(5)), have been synthesized and characterized by elemental analysis, IR, TGA and single-crystal X-ray diffraction. X-ray structural analysis reveals that compounds 1 and 2 are isomorphous and feature 3D networks showing five-connected distorted BN topology, while the isostructural 3-5 display 2D layer structures with two kinds of 13-membered rings. The comparison of Ln–O average bond lengths in compounds 1-5 and other Ln–citrate compounds containing one only ligand reported in the literatures shows that the Ln–O average bond lengths decrease as atomic numbers of Ln increase (except Nd). This trend is in agreement with lanthanide contraction rule. Variable-temperature magnetic susceptibility measurements for compounds 1 and 5 indicate there are antiferromagnetic interactions between magnetic centers. Compound 5 presents Er(III) characteristic emission in the NIR region.2. Five 3D lanthanide(III) compounds with 5-sulfosalicylic acid (H3SSA) as bridging ligands, [Ln(SSA)(H2O)2]n [Ln = Ce(6), Pr(7), Nd(8), Dy(9) and Pr0.5+Nd0.5 (10)], have been synthesized and characterized by elemental analysis, IR, XRD and single-crystal X-ray diffraction. X-ray structural analysis reveals that isostructral compounds 6-10 possess 3D structures with 4664 topology. H3SSA exhibits a new coordination mode. Complexes 6-10 exhibit broad intraligand fluorescent emission bands. Complexe 8 also presents Nd(III) characteristic emission in the near-IR region and complexe 9 presents sensitized luminescence of Dy(III) ions in the visible region. There are weak antiferromagnetic interactions between the Pr(III) ions in 7, between the Nd(III) ions in 8. There exists ferromagnetic interaction between the Dy(III) ions in 9.3. Five rare earth coordination polymers, [(Him)Ln(ip)2(H2O)]n [Ln = La(11), Pr(12), Nd(13) and Dy (14)] and [Y2(ip)3(H2O)2]n·nH2O (15) [H2ip = isophthalic acid, im = imidazole], have been synthesized and characterized by elemental analyses, IR, UV-NIR and single-crystal X-ray diffraction analyses. The isostructural compounds 11-14 possess 3-D structures with three different kinds of channels. Compound 15 features a 2-D network making of two different kinds of quadruple-helical chains. Compounds 12 and 13 present the characteristic emissions of Pr(III) and Nd(III) ions in NIR region, respectively. Compound 14 shows sensitized luminescence of Dy(III) ions in visible region. There are weak antiferromagnetic interactions between the Pr(III) ions in 12, between the Nd(III) ions in 13, between the Dy(III) ions in 14.4. Two rare earth coordination polymers, [Ln(ox)0.5(pdc)(H2O)2]n·nH2O [Ln = Pr(16) and Dy(17), H2ox = oxalic acid,H2pdc = Pyridine-3,5-dicarboxylic acid] and three rare earth compounds, (H2pip)3Ln2(pdc)6(H2O)20 [Ln = Pr(18), Nd(19) and Dy(20), H2pdc = Pyridine-2,6-dicarboxylic acid, pip = piperazine], have been in detail described. There exists 1D channel in the 3D structure. The crystal water fills in the 1D channel. The isostructural compounds 16 and 17 possess 3D structures with interesting topological networks. The compounds 18-20 display an interesting 3D supramolecular network through hydrogen bonding. Interestingly, there exists a 2D water layer in the 3D supramolecular network. Complexes 18-20 exhibit broad intraligand fluorescent emission bands.