Ferrocene-based compartmental ligand for the assembly of neutral ZnII/LnIII heterometallic complexes

A ferrocene-based compartmental ligand, H2L, was synthesized by the reaction of diacetyl ferrocene with hydrazine hydrate followed by a condensation reaction with o-vanillin. [L](2-) possesses a dual coordination pocket, an inner pocket of 2 imino nitrogens and two phenolate oxygens and an outer pocket of two phenolate and two methoxy oxygen atoms. Utilizing this ligand, several Zn-II/Ln(III) heterobimetallic complexes were assembled: [LZn(mu-OAc) Dy(NO3)(2)] (2), [LZn(mu-OAc)Tb(NO3)(2)] (3), [LZn(mu-OAc)Gd(NO3)(2)center dot 2CHCl(3)] (4), [LZn(mu-OAc)Er(NO3)(2)] (5), [LZn(mu-OAc)Ho(NO3)(2)] (6), [LZn(mu-OAc)Eu(NO3)(2)] (7). All of these metal complexes are neutral and isostructural: the Zn-II ion occupies the inner coordination pocket while the Ln(III) ion occupies the outer coordination pocket of the doubly deprotonated ligand [L](2-). Zn(II) has a coordination number of 5 (2N, 3O) in a square pyramidal coordination geometry while Ln(III) has a coordination number of 9 (9O) in a distorted tricapped trigonal prismatic geometry. Zn(II) and the 4f metal ion are bridged to each other by two phenolate oxygen atoms and an acetate ligand. ESI-MS reveals that 2-7 retain their structural integrity in solution. Cyclic voltammetry of 1-7 revealed a quasi-reversible oxidation (involving the ferrocene motif) and an irreversible reduction of the hydrazone unit. Magnetic studies of 2, 3 and 6 were carried out. Ac susceptibility studies did not reveal slow relaxation of magnetization.