Structural characterisation, EPR and magnetic properties of f-f and f-d lanthanide(III) phenolic cryptates

The Schiff base axial macrobicyclic ligand L-1 forms 4f-4f and 4f-3d cryptates with formula [Gd-2(L-1 - 3H)(NO3)(2)]-( NO3).1.5H(2)O (1), [Tb-2(L-1 - 3H)(NO3)(2)](NO3).3EtOH.H2O (2), [GdCu(L-1 - 3H)(NO3)](NO3).H2O(3), [LuCu(L-1 - 3H)(NO3)](NO3).H2O (4) and [GdZn(L-1 - 3H)(NO3)](NO3).H2O (5). The macrobicyclic receptor L-1 is an azacryptand N[(CH2)(2)N=CH-R-CH=N-(CH2)(2)](3)N (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-C-3 symmetries around the metals. In the solid state, the conformation of the cation in 1 and 2 is Lambda(deltadeltalambda)(5)(deltadeltalambda)(5) or its enantiomeric form Lambda(lambdalambdadelta)(5)(lambdalambdadelta)(5), while in 3, 4 and 5 it can be described as Lambda(deltadeltalambda)(5)(delta'delta'delta')(5) (or Lambda(lambdalambdadelta)(5)(lambda'lambda'lambda')(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(L-2 - 3H)(DMF)](ClO4)(2).MeCN. In spite of the similar coordination environment of the Gd() 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.