Synthesis of lanthanide(III) complexes of 20-membered octaaza and hexaaza Schiff-base macrocycles†

Abstract

Mononuclear lanthanide(III) complexes of the 20-membered octaaza Schiff-base macrocycle, 3,9,17,23-tetramethyl-2,10,16,24,29,30,31,32-octaazapentacyclo[23.3.1.1^4,8.1^11,15.1^18,22]dotriaconta-1(29),2,4,6,8(30),9,11,13,15(31),16,18,20,22(32),23,25,27-hexadecaene (L⁶), have been synthesized by the condensation of 2,6-diacetylpyridine and 2,6-diaminopyridine in the presence of lanthanide(III) templates. The complexes [La(L⁶)(NO₃)(H₂O)₃][NO₃]₂·2H₂O, [Ln(L⁶)(NO₃)(H₂O)₂][NO₃]₂·nH₂O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er or Y; n = 2 or 3), [Ln(L⁶)(ClO₄)₂(H₂O)]ClO₄·3H₂O and [Ln(L⁶)(CH₃CO₂)₃(H₂O)]·3H₂O (Ln = Eu or Tb) have been synthesized by using the lanthanide(III) nitrate, perchlorate or acetate as the metal template. The complexes [Dy(L⁶)(NO₃)(ClO₄)]NO₃·H₂O and [Ln(L⁶)(NO₃)(NCS)]NO₃·H₂O (Ln = Eu or Tb) have been synthesized by anion metathesis of the respective (nitrato)(aqua) complex with perchlorate or thiocyanate. For the 20-membered hexaaza macrocycle, 6,20-dichloro-2,10,16,24,29,31-hexaazapentacyclo[23.3.1.1^4,8.1^11,15.1^18,22]dotriaconta-1(29),2,4,6,8(30),9,11,13,15(31),16,18,20,22(32),23,25,27-hexadecaene-30,32-diol (H₂L⁷), complexes have been synthesized by the condensation of 4-chloro-2,6-diformylphenol and 2,6-diaminopyridine in the presence of lanthanide(III) nitrates yielding [Ln(HL⁷)(NO₃)(H₂O)₂]NO₃·nH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er or Y; n = 3 or 4). The formation of lanthanide(III) complexes of L⁶ and H₂L⁷ demonstrates the template potential of the lanthanide(III) cations in the assembly of ‘2 + 2’ symmetric Schiff-base macrocycles having pyridine or phenol head units and pyridine lateral units.