PREPARATION, STRUCTURE, AND LUMINESCENCE OF DINUCLEAR LANTHANIDE COMPLEXES OF A NOVEL IMINE AMINE PHENOLATE MACROCYCLE

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.sN8O19.2Pr2), a = 21.780(4) angstrom, b = 12.444(2) angstrom, c = 17.151(3) angstrom, beta = 107.32(3)degrees, V = 4438 angstrom, 3 and Z = 4. For 2282 observed data, R(w) = 0.039 and R = 0.037. The decacoordination geometry of the identical Pr3+ ions is a C2v 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)4.1.2CH3OH and (La0.97Tb0.03)22(NO3)4.1.2CH30H compounds exhibit strong Tb3+ (5D4 --> 7F(J)) 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 Tb3+ in luminescent diagnostic agents. At room temperature the complex decay kinetics of Tb3+ in Tb22(NO3)4.1.2CH30H are similar to those of Tb21(NO3)4.H2O (Chem. Abstr. 1992, 117, 100045w). But for the dilute complex, (La0.97Tb0.03)22(NO3)4.1.2CH3OH, unusual thermal equilibration of the ligand triplet and Tb3+ 5D4 states occurs at room temperature; the ligand-to-Tb3+ energy-transfer rate is almost-equal-to 4.36 X 10(4) s-1, while Tb3+-to-ligand back-energy-transfer is almost-equal-to 7.1 X 10(4) s-1.