Metal Complexes of Pendant-Arm Macrocyclic Ligands

A series of tris-alcohol substituted triazamacrocyclic ligands has been prepared, with the purpose of investigating the effect of increasing steric strain upon the physical and spectroscopic properties of the resulting first row transition metal complexes. The ligands all contain N3O3 donor sets and are potentially hexadentate. With pendant-arm hydroxyl groups, the ligands may behave as alcohol donors or alkoxide donors. At low pH values the ligands remain protonated and act as alcohol donors, at high pH values deprotonation occurs an the ligands behave as alkoxides, with a concomitant increase in pi-basicity

The Uses of Argument in Mathematics

Stephen Toulmin once observed that `it has never been customary for philosophers to pay much attention to the rhetoric of mathematical debate'. Might the application of Toulmin's layout of arguments to mathematics remedy this oversight? Toulmin's critics fault the layout as requiring so much abstraction as to permit incompatible reconstructions. Mathematical proofs may indeed be represented by fundamentally distinct layouts. However, cases of genuine conflict characteristically reflect an underlying disagreement about the nature of the proof in question.Comment: 10 pages, 5 figures. To be presented at the Ontario Society for the Study of Argumentation Conference, McMaster University, May 2005 and LOGICA 2005, Hejnice, Czech Republic, June 200

Synthesis and characterisation of phosphorescent rhenium(I) complexes of hydroxy- and methoxy-substituted imidazo[4,5- f ]-1,10-phenanthroline ligands

Eight new fluorescent ligands (L1-L8) derived from the fused imidazo[4,5-f]-1,10-phenanthroline core, have been synthesised utilising a one-pot methodology. The ligands include two points of structural variety, allowing multiply-substituted aryl groups (including hydroxy and methoxy moieties) to be attached to the ligand core. The ligands L1-L8 are fluorescent (λem = 399–426 nm) and react with pentacarbonylbromorhenium to give coordination complexes of the form fac-[ReBr(CO)3(NˆN)] (where NˆN = L1-L8). The complexes were characterised using a variety of spectroscopic and analytical techniques, including single crystal X-ray diffraction studies on two examples. The rhenium complexes were all found to be luminescent, revealing classical 3MLCT emission at 579–587 nm in aerated solution with corresponding lifetimes in the range 149–166 ns

Ligand tuneable, red-emitting iridium(III) complexes for efficient triplet-triplet annihilation upconversion performance

A series of substituted 2‐phenylquinoxaline ligands have been explored to finely tune the visible emission properties of a corresponding set of cationic, cyclometalated iridium(III) complexes. The electronic and redox properties of the complexes were investigated using experimental (including time‐resolved luminescence and transient absorption spectroscopy) and theoretical methods. The complexes display absorption and phosphorescent emission in the visible region attributed to MLCT transitions. The different substitution patterns of the ligands induce variations in these parameters. TD‐DFT studies support these assignments and show that there is likely to be a strong spin‐forbidden contribution to the visible absorption bands at 500‐600 nm. Calculation also reliably predict the magnitude and trends in triplet emitting wavelengths for the series of complexes. The complexes were assessed as potential sensitizers in triplet‐triplet annihilation upconversion experiments using 9,10‐diphenylanthracene as the acceptor, with the methylated variants performing especially well with impressive upconversion quantum yields up to 39.3 %

Evaluating π-π stacking effects in macrocyclic transition metal complexes using EPR techniques

The HYSCORE spectra for two different macrocyclic transition metal complexes, namely cobalt tetraphenylporphyrin (CoTPP) and a copper Salen derivative ([Cu(1)]), were examined in relation to their interactions with pyridine (Py) and methylbenzyl amine (MBA), respectively. In both cases weak hyperfine interactions were detected by HYSCORE, but the origin of these interactions was found to originate from completely different effects. In the CoTPPpy adduct, with axial coordination of the substrate (pyridine) to the metal centre, weak couplings from the pyrrole nitrogens of a neighbouring porphyrin complex were identified, and confirmed through a series of isotopic labelling and dilution experiments. This result represents the first ever identification by HYSCORE of π-π interactions between such porphyrin complexes in solution. In the [Cu(1)]MBA adduct, again with axial coordination of the substrate (MBA) to the copper centre, weak couplings were also identified in the HYSCORE spectra, which could easily be misinterpreted as arising from inter-molecular interactions between adjacent ligands. However, the origin of these couplings was clearly demonstrated to arise from intramolecular 13C-ligand interactions. These results demonstrate not only the sensitivity of the HYSCORE technique for detection of weak inter- and intra-molecular interactions in macrocyclic transition metal complexes, but additionally the need to consider dilution effects in the spectral assignments

Aqueous solutions of transition metal containing micelles

Incorporation of d- or f-block metals into ligand systems that renders a metal complex surface-active or drives its partitioning into surfactant phases enables the localisation of chemical functionality at interfaces. This article discusses a number of fundamental aspects of these interesting materials and examines potential applications