Synthesis, Structure And Properties Of Functional Coordination Polymers Based On Arylpolycarboxylate Ligands

In recent years, coordination polymers (CPs) have been great interest for chemists not only because of their many practical applications in luminescence, magnetism, gas storage and heterogeneous catalysis as new materials, but also due to their impressive structural diversity in architectures. So far, various CPs have been successfully synthesized and characterized. The arylpolycarboxylate ligands have recently attracted much interest owing to their diverse coordination modes with metal ions, and the fact that the molecular architecture can be altered with the coordination habits of the metal ions. In addition, they provide the possibility of hydrogen bonds and π-π aromatic stacking interactions, which contribute to the higher-dimensional supramolecular structures. In this paper, we employed three arylpolycarboxylate ligands, including biphenyl-3,3’,5-tricarboxylic acid (H3bpta), 3-(2,4-dicarboxylphenyl)-2,6-dicarboxyl-pyridine (H4dpdp), and 1H-benzimidazole-5,6-dicarboxylic acid (H3Bidc) to construct 32 novel CPs under hydrothermal conditions:[Ln(bpta)(H2O)5·(H2O)3]n (1), [Ln(bpta)(H2O)5·(H2O)2.5]n (2), [Nd(bpta)(H2O)5·(H2O)1.75]n (3), [Sm(bpta)(H2O)5·(H2O)0.5]n (4), [Ln(bpta)(DMF)(H2O)3· (H2O)]n [Ln=Eu(5), Gd(6), Tb(7), Dy(8)], [Zn3(bpta)2(H2O)7·5H2O]n(9), [Zn2(bpta)(bip)2Cl·2H2O]n (bip= 2,6-bis(imidazole-1-yl)pyridine)(10), [Mn3(bpta)2(bip)2]n(11), [La(Hdpdp) (H2O)2·2H2O]n(12), [Ln2(Hdpdp)2 (H2O)4·H2O]n [Ln= Sm(13), Eu(14)], [Ln(Hdpdp)(H2O)3·H2O]n [Ln= Gd(15), Tb(16), Dy(17), Ho(18), Er(19)], [Ln2Co(HBidc)2(SO4)2·(H2O)8]n[Ln= Pr (20), Eu (21), Gd (22), Tb (23), Dy (24), Ho (25), Er (26)], [Gd2Mn(HBidc)2(SO4)2·(H2O)7]n (27) and [Ln2Mn(HBidc)2(SO4)2·(H2O)8]n[Ln= Ho (28), Dy (29), Sm (30), Tb (31), Eu (32)], and the crystal structure, luminescence and magnetic properties have also been investigated. The main work and resuls are as follows:Complexes 1-9 were prepared based on H3bpta with Ln3+(Zn2+), and 10-llbased on a combination of H3bpta and bip with Zn2+ or Mn2+. X-ray crystal structure analyses revealed that 1-9 form a 1D linear chain, and assemble into a 3D supramolecular network structure through hydrogen bonds and π-π stacking among chains. Complexes 10-11 form a 2D layer and 11 further extends to a 3D supramolecular network structure through C-H…O hydrogen bonding and C-H…π interactions. The luminescence of 3-5 and 7-10 was studied, yielding the typical emission spectra for lanthanide-centered luminescence for 3-5 and 7-8. By evaluating the lifetime behavior complex 7 as function of temperature, the different non-radiative decay.paths were discussed. Study of magnetism show compounds 4 and 5 exhibited strong spin-orbit couplings, while weak antiferromagnetic couplings exist in 6. The negative J value of 11 indicates the presence of antiferromagnetic coupling between the Mn(II) ions within a trinuclear unit.Complexes 12-19 were synthesized based on H4dpdp with Ln3+. X-ray crystal structure analyses revealed that 12-19 form a 2D layer and further assemble into a 3D supramolecular network structure through O-H…O hydrogen bonds. The luminescence of 13-14 and 16-17 show the typical emission and excitation peaks at the expected positions for the relevant 4fn-4fn electronic transitions in the trivalent lanthanides.Complex 20-32 were constructed based on H3Bidc with Ln3+ and Co2+ or Mn2+. X-ray crystal structure analyses revealed that 20-32 are a series of Ln-Co(Mn) heterometallic organic framework containing a three-dimensional 4,4-connected PtS-type topology. The study of their photophysical properties show that complexes 21,23-24 and 28-32 display characteristic lanthanide-centered luminescence with low quantum efficiency, presumably due to the crowded energy level structure of these transition metal ions or the presence of water molecules. Besides, ac magnetic susceptibility shows that complex 24 may be a single molecule magnet.Above all, functional coordination polymers from 1D,2D to 3D were designed and prepared by varying the steric hindrance of the arylpolycarboxylate ligands and controlling the reaction condition. The fluorescence and magnetic properties of complexes were discussed in detail to proide theoretical basis for further application as functional materials.