From Gas Phase Observations to Solid State Reality: The Identification and Isolation of Trinuclear Salicylaldoximato Copper Complexes

Conditions have been identified in which phenolic aldoximes and ketoximes of the types used in commercial solvent extraction processes can be doubly deprotonated and generate polynuclear Cu complexes with lower extractant:Cu molar ratios than those found in commercial operations. Electrospray mass spectrometry has provided an insight into the solution speciation in extraction experiments and has identified conditions to allow isolation and characterization of polynuclear Cu-complexes. Elevation of pH is effective in enhancing the formation of trinuclear complexes containing planar {Cu₃-μ₃-O}⁴⁺ or {Cu₃-μ₃-OH}⁵⁺ units. DFT calculations suggest that such trinuclear complexes are more stable than other polynuclear species. Solid structures of complexes formed by a salicylaldoxime with a piperidino substituent ortho to the phenolic OH group (L⁹H₂) contain two trinuclear units in a supramolecular assembly, {[Cu₃OH(L⁹H)₃(ClO₄)](ClO₄)} ₂, formed by H-bonding between the central {Cu₃-μ₃-OH}⁵⁺ units and oxygen atoms in the ligands of an adjacent complex. Whilst the lower ligand:Cu molar ratios provide more efficient Cu-loading in solvent extraction processes, the requirement to raise the pH of the aqueous phase to achieve this will make it impractical in most commercial operations because extraction will be accompanied by the precipitation (as oxyhydroxides) of Fe(III) which is present in significant quantities in feed solutions generated by acid leaching of most Cu ores.

The structural manipulation of a series of Ni4 defective dicubanes: Synthesis, X-ray Structures, Magnetic and Computational analyses

We report the synthesis and characterization of four new tetranuclear Ni(ii) complexes, C1-C4, all of which exhibit defective dicubane cores. C1-C4 are derived from the same salicylaldoxime derived ligand, H2L1. Complexes C1 and C4 have isostructural cores, differing in structure only by solvate molecules. Magnetic and computational analyses have revealed that complexes C1, C2, and C4 exhibit competing ferro- and antiferromagnetic interactions, however the different solvated species in C1 and C4 leads to notably different magnitudes in their magnetic coupling constants. Theoretical magneto-structural studies show that the pairwise magnetic exchange interaction is highly dependent on the Ni-X-Ni angle, as revealed by orbital overlap calculations.

New salicylaldoximato-borate ligands resulting from anion hydrolysis and their respective copper and iron complexes

Anion hydrolysis reactions between salicylaldoximato ligands (L'-L''') and copper and iron BF₄^- metal salts, have resulted in the formation of new salicylaldoximato borate containing transition metal complexes: [Fe₂(L' + 2H)₂](BF₄)₂(MeOH)₄ (C1), [Fe₃(L'' + 4H)(OH)₂(Py)₂](BF₄)₂(H₂O)₂(Py)₂ (C2), and [Cu₂(L''' + H)₂Cl₂] (C3). Each of the complexes have been structurally characterised, revealing the indirect role boron plays in the formation of these complexes. For complexes C1 and C2, Mössbauer spectroscopy confirmed the existence of Fe(iii) oxidation states. SQUID magnetometry measurements were performed on complexes C2 and C3, revealing the presence of two competing exchange pathways between the three Fe(iii) centres in C2, with antiferromagnetic exchange dominating. For C3 weak antiferromagnetic exchange dominated between the two Cu(ii) centres.

The synthesis of three new Cu5, Cu8 and Cu12 clusters via the use of a semi-flexible aminotriazine-based bis-methylpyridine ligand

The use of a semi-flexible aminotriazine-based bis-methylpyridine ligand afforded three new Cu₅, Cu₈ and Cu₁₂ complexes.