Syntheses, Structures And Properties Of Lanthanide Complexes Based On Pyrazine Carboxylic Acid

A series of pyrazine-2,3,5,6-tetracarboxylate alkali-lanthanide metal-organicframeworks, namely,[NaLn(pztc)(H2O)3]·H2O [Ln=Ce (1), Sm (2), Eu (3), Gd (4) andTb (5); H4pztc=pyrazine-2,3,5,6-tetracarboxylic acid] have been synthesized byreacting Ln(NO3)3·6H2O with H4pztc in the presence of NaOH under room temperature.X-ray crystallographic analysis reveals that complexes15are isostructural featuringthree-dimensional (3D) networks with a unique (4116882)(43628)(43) topology inwhich the ligand displays a novel μ7-coordination mode. The photoluminescence (PL)spectra in the solid state reveal that complexes2,3and5exhibit the characteristicluminescence of Sm(III), Eu(III) and Tb(III) ions, respectively, while complex4displays a broad band in the range of400650nm (λmax=505nm) which exhibits about103nm red-shift and enhancement compared to the band of the free ligand. Further, theisostructural two component Eu(III)-doped Gd(III) complexes realize color-tunableluminescence from red to yellow, white, green and blue by variation of excitationwavelengths. It presents the first example towards full-color-tunable emission inlanthanide metal-organic frameworks (LnMOFs) by variation of excitation light.Three novel alkali-lanthanide heterometal-organic frameworks, namely,[K5Ln5(pztc)5(H2O)19]·7H2O [Ln=Dy (6), Ho (7) and Yb (8); H4pztc=pyrazine-2,3,5,6-tetracarboxylic acid] have been facilely synthesized. X-raycrystallographic analysis reveals that complexes68are isostructural featuring unique3D open frameworks, which possess a rare (4,8)-connected net with the Schl fli symbolof (4156128)(456)2. The3D coordination framework involves ladder-like squarecolumns structure by pztc4–ligands bridging metal ions, exhibiting1D channels alongthe b axis. The magnetic analysis suggests that complexes6and8exhibitfrequency-dependent out-of-phase signals in alternating current magnetic susceptibilitymeasurements indicating their slow magnetic relaxation characteristics. It is the firstreport of slow magnetic relaxation behavior existing in Yb3+based HMOF.One pyrazine-2,3-dicarboxylic acid Ag+homometallic framework,[Ag4(pzdc)2]·H2O (9) and five Ln Ag heterometallic frameworks, namely, [Gd2Ag6(pzdc)6(H2O)9]·8H2O (10) and [LnAg(pzdc)2(H2O)2]·nH2O [Ln=Tb, n=2.5(11); Ln=Dy, n=2(12); Ln=Ho, n=2(13); Ln=Er, n=2(14); H2pzdc=pyrazine-2,3-dicarboxylic acid] have been synthesized under room temperature.Complex9exhibits3D metal organic framework (MOF) by Ag2ions connecting1Dsquare columns consisted of Ag1ions and pzdc2ligands, possessing a unique trinodal(3,6)-connected net with {426}{43}{456483103} topology. Complex10displays3Dheterometal organic framework (HMOF) with a novel twelve-nodal (3,4)-connectedtopological net constructed by Gd1ions linking the adjacent Ag-pzdc2anion layers.Complexes1114are isostructural2D Ln Ag heterometallic frameworks featuringuninodal4-connected net with {4462} topology. The magnetic analyses suggest thatcomplexes12and14exhibit field-dependent slow magnetic relaxation, which representthe first slow magnetic relaxation behavior existing in Er3+-based2D heterometallicframework, extending the recent reports on the structure and the single moleculemagnets (SMMs) of f d heterometallic coordination polymers.