Structural variations in (CuL) 2 Ln complexes of a series of lanthanide ions with a salen-type unsymmetrical Schiff base(H 2 L): Dy and Tb derivatives as potential single-molecule magnets

A new series of heterometallic trinuclear Cu Ln complexes [lanthanide ions Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)] has been synthesized using a Cu(ii)-metalloligand derived from a N O donor unsymmetrical Schiff base, H L (where H L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), and structurally characterized. Among these complexes, [(CuL) Gd(NO ) (CH CN) ] (1), [(CuL) Tb(NO ) (CH CN) ] (2) and [(CuL) Dy(NO ) (CH CN) ] (3) are isomorphic and isostructural. In these complexes two metalloligands coordinate to the central Ln(iii) (Ln = Gd, Tb and Dy respectively) ion in a transoid fashion viaμ -phenoxido oxygen atoms. The Ln(iii) ions are deca-coordinated with a distorted tetradecahedron geometry. The two terminal Cu(ii) ions of the complexes possess a hexa-coordinated distorted octahedral geometry. In contrast, in complexes [(CuL) Ho(NO ) (CH CN)], (4) and [(CuL) Er(NO ) (CH CN)]·0.5(CH CN) (5), the two metalloligands coordinated to the Ln(iii) ions in a cisoid fashion. The Ho(iii) ion in 4 is nona-coordinated with a distorted tricapped trigonal prismatic geometry and the Er(iii) ion in 5 is octa-coordinated with a distorted square antiprismatic geometry. The two terminal Cu(ii) ions in complexes 4 and 5 are penta-coordinated with a distorted square-pyramidal geometry. The dc magnetic susceptibilities and field dependent magnetization measurement of complex 1 reveal the occurrence of ferromagnetic interactions between Cu(ii) and Gd(iii) ions as well as intermolecular antiferromagnetic interactions. Both complexes 2 and 3 show ferromagnetic interactions between Cu(ii) and Ln(iii) ions. The ac magnetic susceptibilities of all the complexes were also recorded and it was found that only complexes 2 and 3 exhibit slow relaxation of magnetization reorientation below 10 K at 2000 Oe applied dc field, this being characteristic of single molecule magnets.