A lanthanide-templated Schiff-base condensation reaction to give a trinuclear macrocyclic complex

Abstract

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