Lanthanoid complexes of a tripodal acetal ligand: Synthesis, structural characterisation and reactivity with 3d metals

A novel tripodal ligand (H₃L¹) has been prepared by condensation of tris(2-aminoethyl)amine with 2,6-diformyl-4-methylphenol in MeOH. The compound has three equivalent side-arms, each containing four possible donor groups, an imine N atom, a phenol O atom and two O-donors from an acetal group. The crystal structure showed the arms to be arranged such that a non-crystallographic three-fold axis passes through the bridgehead N atom. Reaction of H₃L¹ with lanthanoid perchlorate salts resulted in the isolation of two series of complexes. With early lanthanoids compounds of stoichiometry [Ln(H₃L¹)(H₂O)][ClO₄]₃ were obtained and the compounds with Ln = La and Pr have been structurally characterised. The lanthanoid site in these complexes is ten co-ordinate, with a geometry which can be related to an icosahedron. For later lanthanoids, complexes of stoichiometry [Ln(H₃L¹)][ClO₄]₃ are found in which the lanthanoid site is nine-co-cordinate, with a tricapped trigonal-prismatic geometry. The complex with Ln = Y has been characterised by diffraction techniques. Mass spectroscopic studies indicated that the acetal functions within H₃L¹ are stabilised by co-ordination to the lanthanoid metals. Reaction of the complex [La(H₃L¹)(H₂O)][CIO₄]₃ with nickel(II) perchlorate led to a novel heterobimetallic complex in which both La and Ni are encapsulated within the tripodal ligand.