Syntheses, Structures And Photoluminescent, Catalytic And Magnetic Properties Of Rare Earth Coordination Polymers

Rare earth coordination polymers (RE-CPs) have received great attention, as animportant member of the coordination polymers (CPs) family, since their richcoordination characteristics and exceptional optical and magnetic properties arisingfrom their4f electrons. Compared with transition metal ions, the lanthanide ionspossess higher coordination numbers and more flexible coordination geometries,leading to the formation of coordination polymers with versatile motifs, such as{[Sm(L)2(NO3)3]·0.5H2O}∞and {[Er2(L)3(NO3)6]·2CH3OH}∞(L=4,4′-bipyridine-N,-N′-dioxide). The former showed rare two-fold interpenetrating three-dimensionalCdSO4-like nets, and the latter showed an unprecedented two dimensional4.82network. Optical fluorescent assays are ubiquitous in biotechnology and medicinalchemistry. RE-CPs have been used extensively as optical materials or analyticalsensors owing to their strong and easily detected emissions at visible andnear-infrared region (NIR). For instance, Eu(III) or Tb(III) compounds, havingcharacteristic emission of red or green luminescence, have long been recognized forthe detection of numerous analytes in biological samples. At the same time, NIRemission of Nd(III) and Er(III) compounds has been used in fibre-opticcommunications based on silica fibers that transmit and boost their signals in the1300-1550nm region. RE-CPs can act as heterogeneous Lewis acid catalysts becausethey can provide the coordinative unsaturated nodes or form the active metal omplexes incorporated into the linker ligands. Recently, scandium coordinationpolymers (ScCPs) with thermally stable framework have been proved to possessinteresting catalytic properties in the green chemistry. For example, Snejko hasprepared a new hybrid organic-inorganic polymer Sc2(OOCC2H4COO)2.5(OH), it canbe used as an effective Lewis acid catalyst and can be easily recycled and reusedwithout any appreciable loss in activity. Therefore, rationally design and constructionof LnCPs with desired geometries and properties is still a challenge.Reaction of3,3′,5,5′-biphenyltetracarboxylic acid (H4BPTC) with variouslanthanide ions, seven novel three dimensional (3D) LnCPs have been prepared undersolvothermal conditions, namely,[Ln3(BPTC)3(H2O)2]·3H3O·4H2O·3DMF (DMF=N,N-Dimethylformamide, Ln=Eu (1), Tb (2), Sm (3) Dy(4)),[Nd(BPTC)(H2O)2]·H3O·0.8DMF (5),[Er2(BPTC)(HCOO)3(H2O)2]·(CH3)2NH (6)and [Tm12(BPTC)8(HCOO)11(H2O)10]·10DMF·7(CH3)2NH (7). Combining with thedifferent lanthanide ions and diversity of coordination mood of H4BPTC ligand, sevencompounds display interesting structural characteristics. Of these, compounds1-4areisostructural and demonstrate a unique3D coordination framework containing twotypes of1D channel, which is built by the novel trinuclear [Ln3O22] SBUs. Compound5can be described as a new3D open-framework structure with quadrilateral-shaped1D channels based on [Nd2O16] SBUs. Compound6has a new3D pillar networkfeature constructed by trapezoidal chains cross-linked by bridging BPTC4ligands,whilst compound7exhibits a3D network with a number of rare oval-shaped channelsalong the [101] direction. The H4BPTC ligand exhibits five new coordination modes,which are firstly reported in M-BPTC frameworks. Compounds1-7all display theirtypical emission bands upon irradiation at the ligand band at room temperature.Compounds1-4present strong characteristic emissions in the visible region, of whichcompounds1and2show millisecond luminescence lifetimes. The NIRphotoluminescent of LnCPs is less observed, especially for the Tm(III) compounds.Owing to the good sensitization of H4BPTC ligand, compounds5-7displaynear-infrared region (NIR) with microseconds luminescence lifetimes. In addition,compounds2,5,6and7exhibit global antiferromagnetic behaviors, of which compound5showing a weak ferromagnetic coupling at235K.Six Sc-CPs, that is, the zero-dimensional structure [Sc2(OH)2(L1)2(H2O)4](8)(H2L1=1,2,3-triazole-4,5-dicarboxylic acid), the one-dimensional infinite chainstructure [Sc3(L2)4(H2O)4]·NO3·H2O (9)(H2L2=4,5-imidazole dicarboxylic acid), thetwo dimensional super-molecule structure [Sc(OH)(L3)2(H2O)](10)(HL3=isonicotinic acid), the3D supermolecule homochiral structure[Sc3O(CH3COO)6(HCOO)(H2O)]2H2O (11), the3D structure with hexagonal pore [Sc3O(L4)3(H2O)3(NO3)]·DMF (12)(H2L4=maleic acid) and the three dimensional structure with rhombic pores[Sc2(OH)2(L5)2]·0.05CH3CN (13)(H2L5=thiophene-2,5-dicarboxylic acid) have beensynthesized and investigated. Interestingly,8,9,10,12and13are activeheterogeneous catalysts for the high-yield cyanosilylation of aromatic aldehydes inacetonitrile, especially for p-nitrobenzaldehyde. Moreover, all the catalysts can bereused three times without losing activity or significant mass. bulk crystal samples of11were measured in the solid-state circular dichroism (CD) spectra indicated itshomochiral nature.In conclusion, under solvothermal conditions, thirteen LnCPs have beensuccessfully prepared and characterized. The luminescence emission shows that theligand sensitizes the luminescence of the Ln(III) ions emitting in the visible region forEu(III), Tb(III), Sm(III) and Dy(III) compounds as well as in the NIR for Nd(III),Er(III) and Tm(III) compounds. These six new solid materials (ScCPs) show chemicalstability in various solvents, as well as good Lewis acid catalytic ability forcyanosilylation of aromatic aldehyde by virtue of its coordinative unsaturated metalsites. Moreover, they could be easily recovered by filtration and reused at least inthree cycles without significant loss of yield. It is believed that more LnCPscontaining multi-carboxylate ligands with interesting structures with excellentproperties will be prepared in the future.