Synthesis, Structure, And Performance Of The Lanthanide Meatal-Organic Frameworks

The lanthanide metal–organic frameworks (Ln-MOFs) are attracting much attention, owing totheir excellent performance in luminescence, electricity, magnetism, and catalysis especiallyin luminescence. Lanthanide ions are characterized by a gradual filling of the4f orbitals.The combination of organic ligands and lanthanide ions can obtain diverse geometric patternsand remarkable physical and chemical properties by synergistic effect. In this paper, a seriesof crystalline Ln-MOFs materials are synthesized by the advisable organic ligands andlanthanide ions, and the structure and performance of Ln-MOFs are characterized. The maininnovative work as follows:1. Under conventional reaction conditions, a series of novel Ln-MOFs[Ln(BTPCA)(H2O)]·2DMF·3H2O (Ln=Eu3+(1), Ce3+(2), Pr3+(3), Nd3+(4); DMF=N,N-dimethylformamide) are synthesized using a ligand H3BTPCA(1,1?,1??-(benzene-1,3,5-triyl)tripiperidine-4-carboxylic acid). The readily accessiblemultiple Lewis basic triazinyl N atoms allow for complexation of incoming metal ions guests,and such interactions are established quantitatively and unambiguously. Depending on theinteraction and the resulting perturbation to the electronic structure of the ligand, theefficiency of ligand–to–lanthanide energy transfer is affected, leading to the quenching orenhancement of luminescence. The essentially complete quenching and drastic enhancementof the Eu3+luminescence upon respective incorporation of metal ions into the inherentlyluminescent MOF suggest specifically the potential use of the MOF for metal ions sensing.[Eu(BTPCA)(H2O)]·2DMF·3H2O (1)[Ce(BTPCA)(H2O)]·2DMF·3H2O (2)[Pr(BTPCA)(H2O)]·2DMF·3H2O (3)[Nd(BTPCA)(H2O)]·2DMF·3H2O (4)2. The isostructural Ln-MOFs are synthesized through the spontaneous self-assembly ofH3BTPCA ligands and lanthanide ions (Ln=La3+, Tb3+, Sm3+, etc.). Prompted by theobservation that the different lanthanide ions have identical coordination environment in theseLn-MOFs, we explored and succeeded in the preparation of mixed-lanthanide analogs of thesingle-lanthanide MOFs by way of in situ doping using a mixture of lanthanide salts. Withcareful adjustment of the relative concentration of the lanthanide ions, the color of theluminescence can be modulated, and white light-emission can indeed be achieved. Themechanisms possibly responsible for the observed photophysical properties of thesemixed-lanthanide MOFs are also discussed.[La(BTPCA)(H2O)]·2DMF·3H2O (5)[Sm(BTPCA)(H2O)]·2DMF·3H2O (6) [Tb(BTPCA)(H2O)]·2DMF·3H2O (7)3. The isostructural Gd-MOF (8) is synthesized through H3BTPCA ligands and Gd3+ions.The adjacent Gd3+ions are bridged by carboxylic group of BTPCA ligands to generate a1Dchain structure. The adjacent Gd3+···Gd3+distance is4.046(3), and the Gd3+Gd3+Gd3+angle is171.375(18)°. The magnetic measurements show that8reveales weakferromagnetic interactions, and acts as a cryogenic magnetic refrigerant having magneticentropy change, ?Sm, of20.40J kg1K1(?H=7T at3K).[Gd(BTPCA)(H2O)]·2DMF·3H2O (8)4. An oxalate-and carbonate-based three dimension Ln-MOF[Eu2(CO3)(ox)2(H2O)2]·4H2O (9, ox=oxalate) is synthesized, and demonstrated the firstwater-mediated proton conduction under above100oC without humidity. Although9isneutral, coordinated water molecules are rendered sufficiently acidic by EuIIIto contributeprotons to the adjacent ox groups and thereby enhance the conductivity. The reportedcompound {[Eu(H2O)3]2(ox)3}·4H2O (10) with similar thermostability as9, is used as acomparative study to explain that1D hydrogen-bonding channel of coordinated watermolecules and the adjacent ox groups is critical importance for proton conduction. Thetemperature-dependent photoluminescent (PL) properties of9are pressed to illustrate thecontribution of the coordinated water molecules for proton conduction.[Eu2(CO3)(ox)2(H2O)2]·4H2O (9){[Eu(H2O)3]2(ox)3}·4H2O (10)4. Under conventional reaction conditions, a series of lanthanide-organic complexesbased on polyoxometalates (POMs)[Ln2(DNBA)4(DMF)8][W6O19](Ln=La(11), Ce(12),Sm(13), Eu(14), Gd(15); DNBA=3,5-dinitrobenzoate) are synthesized. These complexesconsist of [W6O19]2-and dimeric [Ln2(DNBA)4(DMF)8]2+cations. The luminescenceproperties of14are measured in solid state and different solutions, respectively. Notably,the emission intensity increases gradually with the increase of solvent permittivity, and thissolvent effect can be directly observed by electrospray mass spectrometry (ESI–MS).[La2(DNBA)4(DMF)8][W6O19](11)[Ce2(DNBA)4(DMF)8][W6O19](12)[Sm2(DNBA)4(DMF)8][W6O19](13)[Eu2(DNBA)4(DMF)8][W6O19](14)[Gd2(DNBA)4(DMF)8][W6O19](15)...