A LANTHANIDE-TEMPLATED SCHIFF-BASE CONDENSATION REACTION TO GIVE A TRINUCLEAR MACROCYCLIC COMPLEX

Template condensation of 2,6-diacetylpyridine with 1,3-diamino-2-hydroxypropane in refluxing methanol in the presence of Ln(NO3)3.xH2O (Ln = La, Pr, Eu or Gd) gives [Ln3L3(OH)2(NO3)4].nH2O (n = 4-7), where L3 is a trianionic Schiff-base macrocyclic ligand formed from three diketone and three diamine units. Analogous reactions with Ln(NCS)3.xH2O (Ln = La, Pr, Eu or Gd) as template give [Ln3L3(OH)(NCS)5]-7H2O, while Ca(NO3)2.xH2O gives [CaL2(NO3)2], where L2 is a ring-contracted '2 + 2' Schiff -base macrocycle. The crystal structure of [La3L3(OH)2(NO3)4].7H2O has been determined [orthorhombic, space group Pbca (no. 61), a = 22.74(2), b = 21.130(5), c = 23.245(6) angstrom; R = 0.081, R' = 0.061]. An approximately equilateral triangle of La atoms (La...La almost-equal-to 4 angstrom) is bridged by a mu3-OH- ligand and encapsulated by the (3 + 3) macrocycle.