A series of bis-salicylidene based N₂S₂ copper macrocycles were prepared, structurally characterised and subjected to electrochemical analysis. The aim was to investigate the effects of length of polymethylene chains between either the imine donors or the sulfur donors on redox state and potential of the metal. The complexes structurally characterised had either distorted square planar or tetrahedral geometries depending on their oxidation state (Cu²+ or Cu+, respectively), and the N–(CH₂)n–N bridge was found to be most critical moiety in determining the redox potential and oxidation state of the copper macrocycles, with relatively little change in these properties caused by lengthening the S–(CH₂)n–S bridge from two to three carbons. In fact, a weakness was observed in the complexes at the sulfur donor, as further lengthening of the S–(CH₂)n–S methylene bridge to four carbons caused fission of the carbon–sulfur bond to give dimeric rings and supramolecular assemblies. Cu+ complexes could be oxidised to Cu²+ by tert-butylhydroperoxide, with a corresponding change in the spectrophotometric properties, and likewise Cu²+ complexes could be reduced to Cu+ by treatment with β-mercaptoethylamine. However, repeated redox cycles appeared to compromise the stability of the macrocycles, most probably by a competing oxidation of the ligand. Thus the copper N₂S₂ macrocycles show potential as redox sensors, but further development is required to improve their performance in a biochemical environment.

The synthesis and structures of bis-((μ²-acetato-O,O)-μ-(N,N'-bis-(o-hydroxybenzyl)-1,3-diaminopropane)-(aquo)nickel)nickel, bis-((μ²-acetato-O,O')-μ-(N,N'-bis-(o-hydroxybenzyl)-1,4-diaminobutane nickel)nickel acetate) and bis-((μ²-acetato-O,O')-μ-(N,N'-bis(o-hydroxybenzyl)-1,4-diaminobutane)-(dimethylformamido)nickel)nickel are reported. These compounds are designed to draw attention to the wider structural catalogue available to symmetrical hydrogenated Schiff base complexes which contain a tetramethylene backbone.

A series of cis and trans tetradentate copper macrocyclic complexes, of ring size 14–16, that employ amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane copper(I) (cis-[Cu(H4NbuSen)]+) all of the complexes are obtained in the copper(II) form. Crystallographic analysis shows that the copper(II) complexes all adopt a distorted planar geometry around the copper. In contrast, cis-[Cu(H4NbuSen)]+ is found to adopt a distorted tetrahedral geometry. The complexes were subjected to electrochemical analysis in water and acetonitrile. The effect of the solvent, positions of the donor atoms (cis/trans) on E1/2 is discussed as is the comparison of the electrochemical behaviour of these complexes with their parent Schiff base macrocycles.

We report a study which correlates the metrical parameters of the unsubstituted tetradentate copper Schiff base complexes containing N₂O₂, N₂N₂ and N₂S₂ donors with their respective redox potentials. To achieve this aim we were required to structurally characterise many of the seminal species including, [CuAmbpr-H₂], [CuH₄Amben][ClO₄]₂, [CuH₄Ambpr][ClO₄]₂, [CuH₄Ambbu][ClO₄]₂, CuH₄Salpr and [Cu(SSalen)₂][ClO₄]₂ which were absent from the crystallographic catalogue. The oxidative dehydrogenation of CuH₄Salen is revisited through the isolation and structural characterisation of (N-salicyl-N'-salicylidene-1,2-ethylenediamine)copper(II) (CuH₃Salen). The redox potentials of the three series of compounds are measured, clearly identifying the operating ranges of each donor set. The modulating effect of coordination geometry on redox potential is evident in the series of N₂O₂ complexes. This study forms the basis of the rational synthesis of tuneable copper redox sensors by demonstrating the regions in which the various donor sets operate.

The synthesis and structure of a homologous series of cationic N₂S₂ copper(I) Schiff base complexes constructed using o-tert-butylthiobenzaldehyde and a series of terminal diamines (ethane, propane, butane) are reported. The complexes differ only in the length of the methylene chain between the imine groups. This simple modification forces the copper centre to shift geometry from a planar (1,2-diaminoethane) to a more distorted tetrahedral motif (1,4-diaminobutane). The redox potentials of the three cations were measured using cyclic voltammetry in donor (acetonitrile) and non-donor solvents (dichloromethane). The S–Cu–N angles for each complex are correlated against the respective redox potential allowing an analysis of the geometric impact on the redox potential in soft copper centres. The redox potential is observed to increase as the metal centre moves from a planar towards a tetrahedral motif. Comparing this data with the reported structures of the blue copper proteins (rusticyanin and plastocyanin) allows an assessment of the contribution of the geometry of the metal binding site to the operating potential of these proteins to be made.