Clegg, Jack K., Bray, David J., Gloe, Kerstin, Gloe, Karsten, Jolliffe, Katrina A., Lawrance, Geoffrey A., Lindoy, Leonard F., Meehan, George V., and Wenzel, Marco (2008) 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-beta-diketonato ligands. Dalton Transactions, 2008. pp. 1331-1340.

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Abstract

Uncharged complexes, formulated as trimeric metallocycles of type [M3(L1)3(Py)6] (where M = cobalt(II), nickel(II) and zinc(II) and L1 is the doubly deprotonated form of a 1,4-phenylene linked bis-b-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 L1 (R = Ph) and copper(II) with L1 (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 [Ni3(L1)3(Py)6]·3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L1, [Co3(L1)3(Py)6], [Ni3(L1)3(Py)6], [Cu3(L1)3], [Zn3(L1)3(Py)6] and [Fe4(L1)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-b-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-b-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).

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