The Synthesis, Structure, Characterization And Luminescence Properties Based On Nicotinic N-oxide Or 1,4-Naphthalene Dicarboxylate Of Lanthanide Metal Organic Coordinations Compounds

(1) Two series of lanthanide(Ⅲ)-organic frameworks with the molecular formula [Ln2(NNO)2(OX)2(H2O)4]n (Ln= Eu 1, Tb 2, Sm 3, Dy 4, Gd 5) and [Ln2(NNO)4(OX)(H2O)2]n (Ln= Eu 6, Tb 7, Sm 8, Dy 9, Gd 10) were synthesized successfully under same hydrothermal conditions with nicotinic N-oxide (HNNO) and oxalic acid (H2OX) as the mixed ligands merely through varying the molar ratio of the reactants. The compounds were characterized by IR, elemental analysis, UV, TG-DTA and powder XRD. X-ray single-crystal diffraction analyses of compounds 1 and 7 selected as representatives and powder XRD analysis of the compounds revealed that both of the two series of compounds feature three-dimensional (3-D) open frameworks, crystallize in triclinic P-1 space group while with different unit cell parameters. In compound 1, pairs of Eu3+ ions and pairs of NNO" ligands connect each other alternately to form a 1-D infinite Eu-NNO double chain, the adjacent 1-D double-chains are then joined together through OX2- ligands leading to a 2D layer, the 2-D layers are further ’pillared’by OX2- ligands resulting in a 3-D framework. In compound 7, the 1-D Tb-NNO infinite chain and its 2-D layer are formed in almost similar fashion to that adopted in compound 1. The difference between the structures of the two compounds 1 and 7 is that the adjacent 2-D layers in compound 7 are further connected by NNO" ligands resulting in a 3-D framework. The photoluminescence properties and energy transfer mechanism of the compounds were studied systematically. The energy level of the lowest triplet states of the HNNO ligand (23148 cm-1) was determined based on the phosphorescence spectrum of compound 5 at 77 K. The 5D0 (Eu3+) and 5D4 (Tb3+) emission lifetimes (0.46 ms,0.83 ms,0.69 ms and 0.89 ms) and overall quantum yields (1.03%, 3.29%,2.58% and 3.78%) for the compounds 1,2,6 and 7, respectively.(2) Lanthanide organic frameworks with nicotinic acid N-oxide (HNNO), {[Ln(NNO)(MA)(H2O)3]·2H2O}n (Ln-Eu 1, Tb 2, Sm 3, Dy 4, Gd 5), were synthesized successfully under the solution conditions, and fully characterized by elemental analyses, IR, UV, powder X-ray diffration (XRD), TG-DTA. The X-ray crystal structure of compound 1 reveals crystallizes in the monoclinic P2(1)/c space group. In compound 1,-OOC-CH2-COO- and Eu3+ connected each other alternatively to form a 1-D chain along b direaction, the adjacent 1-D chains are then joined together through the NNO-ligands forming a 2D layer in be plane then the adjacent 2-D layers are further connected by π-π conjugative effect between adjacent parallel NNO-pyridine ring and resulting a 3D supramolecular structure. The photoluminescent properties the compounds 1 and 2 were studied and the luminescence intensity of 2 is stronger than 1, the rusults in agreement with our energy transfer mechanism study, which the energy level of the lowest triplet states of the HNNO ligand is calculated to be 22935 cm"’(436 nm) indicating HNNO is a suitable sensitizer for the luminescence of Tb3+rather than Eu3+ ion. The 5D0 (Eu3+) and 5D4 (Tb3) emission lifetimes (0.40 ms and 0.56 ms) and overall quantum yields (0.824% and 2.58%) of compound 1 and 2 were determined, respectively, and the sensitization efficiencies (12.69%) of compound 1 were calculated.(3) Millimeter dimensional lanthanide organic frameworks: {Eu2(NDC)3(DMF)4}n 1 were synthesized successfully under hydrothermal conditions with 1,4-naphthalenedicarboxylate (1,4-H2NDC) as the ligand, and fully characterized by elemental analyses, IR, UV, powder X-ray diffration (XRD), TG-DTA. The X-ray crystal structure of {Eu2(NDC)3(DMF)4}n reveals crystallizes in the triclinic P-1 space group,with a 2D layer structure, then the adjacent 2-D layers are further connected by π-π conjugative effect between adjacent parallel NDC2- naphthalene ring and resulting a 3D supramolecular structure.We also synthesised the nanometer and milimeter sized isomorphic (S1-S4) crystal under the assistance of hexadecyltrimethylammonium(CTAB) and triethylamine(TEA) as surfactant. SEM micrographs shows the S2 crystals with regular shape and uniform size of 100-200 nm. The analysis result of IR and powder XRD shows that the compounds of compound 1 and S1-S4 are the same structure. We also studied the growth mechanism of S1-S4 crystal by systematically changing the molar ratio of CTAB and TEA of the solvothermal process. The photoluminescent properties the compounds 1 and S1-S4 were studied and the luminescence intensity of S1-S3 is stronger than 1,the result can be explained by nanometer size effect.