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

Abstract

Uncharged complexes, formulated as trimeric metallocycles of type [M3(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 H2L(1) (R = t-Bu) and of its trinuclear (triangular) nickel(II) complex [Ni3(L(1))3(Py)6].3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L(1), [Co3(L(1))3(Py)6], [Ni3(L(1))3(Py)6], [Cu3(L(1))3], [Zn3(L(1))3(Py)6] and [Fe4(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).

New Cobalt-Mediated Radical Polymerization (CMRP) of Methyl Methacrylate Initiated by Two Single-Component Dinuclear β-Diketone Cobalt (II) Catalysts

“…Another recent paper reports the same compound as a water solvate and argues that it must be trinuclear, like other characterized members having the same stoichiometry [20]–[24].…”

Supramolecular Coordination: Self-Assembly of Finite Two- and Three-Dimensional Ensembles

“…168 While 1,3-phenylene-linked bis-β-diketonato ligands led to the formation of dinuclear metallacycles, 169,170 1,4-phenylene-linked bis-β-diketonato ligands gave trinuclear assemblies. 171,172 These planar ‘platform-like’ macrocycles, upon interaction with ditopic heterocyclic bases, led to the formation of both sandwich-like discrete and extended 3D supramolecular architectures. 173,174 Recently, the same group reported one of the largest neutral triangular supramolecular assemblies.…”

Designed Topology and Site‐Selective Metal Composition in Tetranuclear [MM′⋅⋅⋅M′M] Linear Complexes

“…[19] The use of b-diketone groups as part of ligands has been used also by other groups for the assembly of a variety of coordination complexes. [20][21][22][23][24] We have recently directed our attention towards ligands capable of keeping metals separate into two semi-independent groups within a molecule, since these types of assemblies have been proposed as good candidates to become two-qbit quantum gates for quantum computing. [25] An attractive ligand for this purpose is H 4 L (Scheme 1, top), which exhibits two separate pairs of coordination pockets designed to assemble chains of four metals as two independent dimers.…”