Synthesis of lanthanide(III) complexes of chloro- and bromo substituted 18-membered tetraaza macrocycles

Lanthanide(III) complexes of the chloro substituted 18-membered tetraaza ma crocycle, 14,29-dichloro-3,10,18,25-tetraazapentacyclo[25.3.1.1(12,16).0(4, 9).0(19,24)]dotriaconta-1(31),2,4,6,8,10,12,14,16(32),17,19,21,23,25,27,29- hexadecaene-31,32-diol (H2L4), and the bromo substituted 18-membered tetraa za macrocycle, 14,29-dibromo-3,10,18,25-tetraazapentacyclo[25.3.1.1(12,16). 0(4,9).0(19,24)]dotriaconta-1(31),2,4,6,8,10,12,14,16(32),17,19,21,23,25,27 ,29-hexadecaene-31,32-diol (H2L5), have been synthesized by the template co ndensation of 2,6-diformyl-4-chlorophenol and 2,6-diformyl-4-bromophenol wi th 1,2-diaminobenzene, respectively, in the presence of hydrated lanthanide (III) nitrates in acetonitrile. Discrete mononuclear lanthanide(III) comple xes of the composition [Ln(H2L4)(NO3)(CH3CN)](NO3)(2).nH(2)O (Ln=Nd3+-Tm3and Y3+, except Pm3+; n=1 for Nd3+ and Y3+, n=2 for Sm3+, Gd3+, Tb3+, Dy3+, Ho3+ and Tm3+ and n=3 for Eu3+ and Er3+) and [Ln(H2L5)(NO3)(CH3CN)](NO3)(3 ).nH(2)O (Ln=Sm3+-Tm3+ and Y3+; n=2 for Sm3+, Dy3+, Ho3+ and Er3+ and n=3 f or Eu3+, Gd3+, Tb3+, Tm3+ and Y3+) have been synthesized in 20-35% yield. T he chloro and bromo substituents on the macrocyclic framework do not affect the template potential of the lanthanide(III) cations. The formation of th e complexes of H2L4 and H2L5 with lanthanide(III) ions is due to the adapta bility of these macrocycles to coordinate according to the geometrical requ irements of the metal ions and to the steric demands of the exocyclic ligan ds. The macrocycles coordinate as neutral ligands and the phenolic protons remain intact. The magnetic moments of the complexes are very close to the van Vleck values of the free lanthanide(III) cations. The complexes are sta ble in methanol and DMF over a period of 1 month. The complexes exhibit hig h thermal stability and the coordinated macrocycles are stable up to 360 de grees C. (C) 1999 Elsevier Science Ltd. All rights reserved.