Tetrametallic lanthanide(iii) phosphonate cages: Synthetic, structural and magnetic studies

Abstract

The synthesis, structures and magnetic properties of a family of lanthanide complexes containing phosphonate ligands are reported. Reaction of hydrated lanthanide nitrate and tbutylphosphonic acid under reflux conditions in iso-butanol, in the presence of pivalic acid as a co-ligand produced five new lanthanide complexes; pyridine (py) was present as a base. The compounds formed are tetrametallic, with the general formula [pyH]4[Ln4(μ3-OH)(O3PtBu)3(HO3PtBu)(O2CtBu)2(NO3)6] where Ln = GdIII, 1; TbIII, 2; DyIII, 3; HoIII, 4 and ErIII, 5. The metal sites within the complexes lie on the vertices of a triangle-based pyramid, with phosphonate ligands on the triangular faces linking the apical Ln site to the Ln sites in the base. Each lanthanide(iii) site is eight-coordinate. Magnetic studies of the compounds show a decline in the product χMT with T; modelling the behaviour of 1 shows anti-ferromagnetic exchange between GdIII centres within the triangle with a negligible interaction to the fourth GdIII centre at the apex of the trigonal pyramid.