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[23.3.1.14,8.111,15.118,22]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[23.3.1.14,8.111,15.118,22]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.