Structural Characterization and Magnetic Properties of f-f and f-d Lanthanide(III) Phenolic Cryptates

F. AVECILLA; C. PLATA-IGLESIAS; R. RODRÍGUEZ-CORTINHAS; G. GUILLEMOT; C. D. BRONDINO; C. F. G. C. GERALDES; A. DE BLAS; J. G. BÜNZLI; T. RODRIGEZ-BLAS

JOURNAL OF THE CHEMICAL SOCIETY, DALTON TRANSACTIONS

RCS

Año: 2002 p. 4658 - 4665

0300-9246

The Schiff base axial macrobicyclic ligand L1 forms 4f–4f and 4f–3d cryptates with formula [Gd2(L1 - 3H)(NO3)2]-(NO3).1.5H2O (1), [Tb2(L1 - 3H)(NO3)2](NO3).3EtOH.H2O (2), [GdCu(L1 - 3H)(NO3)](NO3).H2O (3),[LuCu(L1 - 3H)(NO3)](NO3).H2O (4) and [GdZn(L1 - 3H)(NO3)](NO3).H2O (5). The macrobicyclic receptor L1 is an azacryptand N[(CH2)2N=CH–R–CH=N–(CH2)2]3N (R =1,3-(2-OH-5-Me–C6H2)). The crystal structures of the five compounds have been determined by X-ray crystallography. The ligand is helically wrapped around the two metal ions, leading to pseudo-C3 symmetries around the metals. In the solid state, the conformation of the cation in 1 and 2 is Λ(δδλ)5(δδλ)5 or its enantiomeric form Δ(λλδ)5(λλδ)5, while in 3, 4 and 5 it can be described as Λ(δδλ)5(δ´δ´δ´)5 (or Δ(λλδ)5(λ´λ´λ´)5). In 1, only one enantiomer is found in the crystal lattice, whereas in the other four compounds, both enantiomers are co-crystallised. The magnetic behaviour of the homodinuclear (Gd, Gd) and the heterodinuclear (Gd, Cu) cryptates points to a significant magnetic interaction between the two metal ions. This magnetic interaction is antiferromagnetic in the case of the Gd–Gd cryptate 1 (J = -0.194(6) cm-1), but ferromagnetic for the Gd–Cu one (J = 2.2(1) cm-1). The antiferromagnetic coupling observed for 1 is one of the largest ever reported. Although the ferromagnetic coupling observed for 3 is relatively weak, which is attributed to the strong bending of the bridging network, it is considerably stronger than the one reported for [GdCu(L2 - 3H)(DMF)](ClO4)2.MeCN. In spite of the similar coordination environment of the Gd(III) ion in compounds 1, 3 and 5 their EPR spectra are different, thereby confirming the magnetic interactions between the Gd(III) ion and the Cu(II) ion in 3 and the other Gd(III) ion in 1.