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)AR= 0.081, R′= 0.061]. An approximately equilateral triangle of La atoms (La ⋯ La ≈ 4 A) is bridged by a µ3-OH– ligand and encapsulated by the (3 + 3) macrocycle.