Matthews, Karen D.,; Kahwa, Ishenkumba A.; Williams, David J.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Preparation, structure, and luminescence of dinuclear lanthanide complexes of a novel imine-amine phenolate macrocycle
Date of Publication
Metal-free condensation of 2,6-diformyl-p-cresol with 3,6-dioxa-1,8-octanediamine followed by reduction with sodium tetrahydroborate and addition of lanthanide (III) nitrate salts, in that order yield (slowly) crystalline dinuclear complexes of a novel imine-amine phenolate macrocycle 2. The crystals of Ln22(NO3)4.1.2CH3OH are monoclinic, space group C2/c; with Ln=Pr (C31.2H46.8N8O19.2Pr2), a=21.780(4) A, b = 12.444(2) A,c =17.151 (3) A, b = 107.32 (3)°, V=4438 A,3 and Z =4. For 2282 observed data, Rw=0.039 and R=0.037. The decacoordination geometry of the identical Pr3+ ions is a Ccv 4A,6B -extended dodecahedron made up of two bidentate NO3- ions, two phenolate and two ether oxygens, and one imine and one amine nitrogens. Dinuclear lanthanide complexes of 2 appear to be more stable than those of the totally reduced chelate 3 in alcoholic media. The Tb22(NO3)4°1.2CH3-OH and (La0.97Tb0.03)22(NO3)4°1.2CH3OH compounds exhibit strong Tb3+(5D4®7Fj) emission sensitized by the singlet state of 2 at both 77 and 295 K. No Tb3+-Tb3+ self-quenching or N-H trapping effects are observed at 77 K (decay rate is 598 s-1); the coordination cavities of 2 are therefore potentially good hosts for Tb 3+ in uminescent diagnostic agents. At room temperature the complex decay kinetics of Tb3+ in Tb22(NO3)4.1.2CH3OH are similar to those of Tb21(NO3)4.H2O (Chem. Abstr. 1992, 117, 100045w). But for the dilute complex, (La0.97-Tb0.03)22(NO3)41.2CH3OH, unusual thermal equilibrium of the ligand triplet and Tb3+5D4 states occurs at room temperature; the ligand-to-Tb3+ energy-transfer rate is »4.36x104s-1, while Tb3+-to-ligand back energy-transfer is »7.2x104s-1....