Kd. Matthews et al., PREPARATION, STRUCTURE, AND LUMINESCENCE OF DINUCLEAR LANTHANIDE COMPLEXES OF A NOVEL IMINE AMINE PHENOLATE MACROCYCLE, Inorganic chemistry, 33(7), 1994, pp. 1382-1387
Metal-free condensation of 2,6-diformyl-p-cresol with 3,6-dioxa-1,8-oc
tanediamine followed by reduction with sodium tetrahydroborate and add
ition of lanthanide(III) nitrate salts, in that order, yield (slowly)
crystalline dinuclear complexes of a novel imine-amine phenolate macro
cycle 2. The crystals of Ln22(NO3)4.1.2CH3OH are monoclinic, space gro
up 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)degree
s, V = 4438 angstrom, 3 and Z = 4. For 2282 observed data, R(w) = 0.03
9 and R = 0.037. The decacoordination geometry of the identical Pr3+ i
ons 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 amin
e nitrogens. Dinuclear lanthanide complexes of 2 appear to be more sta
ble than those of the totally reduced chelate 3 in alcoholic media. Th
e Tb22(NO3)4.1.2CH3OH and (La0.97Tb0.03)22(NO3)4.1.2CH30H compounds ex
hibit strong Tb3+ (5D4 --> 7F(J)) emission sensitized by the singlet s
tate of 2 at both 77 and 295 K. No Tb3+-Tb3+ self-quenching or N-H tra
pping effects are observed at 77 K (decay rate is 598 s-1); the coordi
nation cavities of 2 are therefore potentially good hosts for Tb3+ in
luminescent diagnostic agents. At room temperature the complex decay k
inetics of Tb3+ in Tb22(NO3)4.1.2CH30H are similar to those of Tb21(NO
3)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 li
gand-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.