Synthetic, structural, electrochemical and solvent extraction studies of neutral trinuclear Co(II), Ni(II), Cu(II) and Zn(II) metallocycles and tetrahedral tetranuclear Fe(III) species incorporating 1,4-aryl-linked bis-β-diketonato ligands

Uncharged complexes, formulated as trimeric metallocycles of type [M-3(L-1)(3)(Py)(6)] (where M = cobalt(II), nickel(II) and zinc(II) and L-1 is the doubly deprotonated form of a 1,4-phenylene linked bis-beta-diketone ligand of type 1,4-bis(RC(O)CH2C(O))C6H4 (R = t-Bu)) have been synthesised, adding to related, previously reported complexes of these metals with L-1 (R = Ph) and copper(II) with L-1 (R = Me, Et, Pr, t-Bu, Ph). New lipophilic ligand derivatives with R = hexyl, octyl or nonyl were also prepared for use in solvent extraction experiments. The X- ray structures of H2L1 (R = t-Bu) and of its trinuclear (triangular) nickel(II) complex [Ni-3(L-1)(3)(Py)(6)]center dot 3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L1, [Co-3(L-1)(3)(Py)(6)], [Ni-3(L-1)(3)(Py)(6)], [Cu-3(L-1)(3)], [Zn-3(L-1)(3)(Py)(6)] and [Fe-4(L-1)(6)] (all with R = t-Bu) show that oxidative processes for the complexes are predominantly irreversible, but several examples of quasireversible behaviour also occur and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as involving metal-centred oxidations. The reduction behaviour for the respective metal complexes is not simple, being irreversible in most cases. Solvent extraction studies (water/chloroform) involving the systematic variation of the metal, bis-beta-diketone and heterocyclic base concentrations have been performed for cobalt(II) and zinc(II) using a radiotracer technique in order to probe the stoichiometries of the respective extracted species. Significant extraction synergism was observed when 4-ethylpyridine was also present with the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies demonstrated a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).