MACROCYCLIC COMPLEXES OF LANTHANIDES IN IDENTICAL LIGAND FRAMEWORKS .1. SYNTHESIS OF LANTHANIDE(III) AND YTTRIUM(III) COMPLEXES OF AN 18-MEMBERED DIOXATETRAAZA MACROCYCLE

Lanthanide(III) and yttrium(III) complexes of the 18-membered dioxatetraaza macrocyclic ligand L(2) are synthesized by the Schiff base condensation of 2,6-diformyl-4-methylphenol with 1,2-diaminobenzene in the presence of hydrated lanthanide(III) nitrate or yttrium(III) nitrate pentahydrate in dry acetonitrile at ambient temperature. Discrete mononuclear lanthanide(III) complexes of the type [Ln(L(2)) (NO3) (H2O)] (NO3)(2) . nH(2)O (Ln = Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+; n = 1 for Pr3+, Nd3+ Sm3+, Eu3+; n = 2 for Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+) and the yttrium(III) complex [Y(L(2)) (NO3) (H2O)] (NO3)(2) . H2O have been synthesized in 28-70% yield in the solid state. The condensation of the same organic precursors in the absence of the metal template yields the diimine-diamine macrocycle L(3) in 65% yield. Reaction of the preformed macrocycle L(3) with hydrated lanthanide(III) nitrate does not yield complexes. The ability of the lanthanide (III) cations to serve as templates in the formation of the complexes of L(2) is attributed to the remarkable ability of this tetraimine macrocycle to adapt to the geometrical requirements of the lanthanide(III) cations. The electronic and steric requirements of the central metal ions appear to be fully satisfied by coordination of the four nitrogen and two oxygen donors of the macrocycle and to the oxygen donors of a bidentate chelating nitrate ion and to a water molecule. The coordination number of the metal ions is 9. The two phenolic protons of the macrocycle remain intact in the complexes. The lanthanide(III) and yttrium(III) complexes of L(2) are stable in methanol over a period of two months. The complexes exhibit high thermal stability and the macrocyclic entity remains unchanged up to 320 degrees C.