No description available.

No description available.

No description available.

No description available.

Ligand–mediated coupling between metal centres is of fundamental importance in inorganic and materials chemistry. Bridging ligands involving azo groups as coordinating π–acceptors can yield complexes with interesting properties. This thesis describes the synthesis of a series of N–heterocyclic compounds containing the azo functionality, designed for potential coordination to the metal through the azo nitrogen and a N–heterocyclic ring. The azo ligands are divided into four categories; ligands based on azobispyridines, ligands containing pyrimidine and fused aromatic azine groups and ligands capable of coordinating in a bis–tridentate fashion to the metal centre. Ligands containing flexible imine subunits connected directly, or through different spacers, are also discussed. Overall twenty one ligands were synthesised, six of which are new compounds. The coordination and metallosupramolecular chemistry of these ligands with ruthenium(II) and silver(I) metal atoms was investigated. A total of thirty five ruthenium(II) and eleven silver(I) complexes were prepared, of which thirty eight were characterised by X–ray crystallography. Mononuclear and dinuclear ruthenium(II) complexes were synthesised and characterised by a combination of spectroscopic and structural techniques. UV/Visible absorption studies and electrochemical methods were used to investigate the nature of metal–ligand and metal–metal interactions. In the mononuclear Ru(II) complexes, N–heterocyclic azo ligands act as chelating ligands forming five–membered chelate rings involving azo–N and heterocyclic–N atoms. The non–coordinated pyridine ring of the azo ligand is twisted with respect to the azo–N atom and is directed towards the adjacent bipyridine rings. Studies reveal that these azo ligands posses extremely low–lying π*–orbitals and are electron deficient. X–Ray structural analysis of the dinuclear complexes revealed short inter–metal separations of ca. 4.9 Å and electrochemical studies indicate that these ligands mediate very strong interactions between the metal centres , due to the excellent π*–acceptor properties of the azo functionality. Varying the pyridine ring of the azo ligand to pyrimidines and fused N–aromatic rings has a considerable effect on the electronic properties of these complexes. Incorporation of a pyrimidine ring facilitates the stabilisation of azo anion radicals and leads to the formation of diruthenium(II) species, bridged by radical species. The X–ray crystal structures of both these complexes were determined. The use of the hexadentate ligands coordinating in a bis–tridentate manner mediate even stronger communication between the two ruthenium centres. Ligands containing bis–pyridylimines result in weaker coupling between the metal centres in dinuclear ruthenium(II) species. A complete absence in the inter–metal communication was observed with increasing the distance and/or flexibility between the two pyridylimine units, contrary to a previous reported claim. Reaction with different silver(I) salts afforded an array of one–dimensional coordination polymers and a discrete dinuclear complex depending on the coordination strengths of the anions. The metallosupramolecular assemblies obtained were characterised mainly by X–ray crystallography, elemental analysis and mass spectrometry.

Ligand–mediated coupling between metal centres is of fundamental importance in inorganic and materials chemistry. Bridging ligands involving azo groups as coordinating π–acceptors can yield complexes with interesting properties. This thesis describes the synthesis of a series of N–heterocyclic compounds containing the azo functionality, designed for potential coordination to the metal through the azo nitrogen and a N–heterocyclic ring. The azo ligands are divided into four categories; ligands based on azobispyridines, ligands containing pyrimidine and fused aromatic azine groups and ligands capable of coordinating in a bis–tridentate fashion to the metal centre. Ligands containing flexible imine subunits connected directly, or through different spacers, are also discussed. Overall twenty one ligands were synthesised, six of which are new compounds. The coordination and metallosupramolecular chemistry of these ligands with ruthenium(II) and silver(I) metal atoms was investigated. A total of thirty five ruthenium(II) and eleven silver(I) complexes were prepared, of which thirty eight were characterised by X–ray crystallography. Mononuclear and dinuclear ruthenium(II) complexes were synthesised and characterised by a combination of spectroscopic and structural techniques. UV/Visible absorption studies and electrochemical methods were used to investigate the nature of metal–ligand and metal–metal interactions. In the mononuclear Ru(II) complexes, N–heterocyclic azo ligands act as chelating ligands forming five–membered chelate rings involving azo–N and heterocyclic–N atoms. The non–coordinated pyridine ring of the azo ligand is twisted with respect to the azo–N atom and is directed towards the adjacent bipyridine rings. Studies reveal that these azo ligands posses extremely low–lying π*–orbitals and are electron deficient. X–Ray structural analysis of the dinuclear complexes revealed short inter–metal separations of ca. 4.9 Å and electrochemical studies indicate that these ligands mediate very strong interactions between the metal centres , due to the excellent π*–acceptor properties of the azo functionality. Varying the pyridine ring of the azo ligand to pyrimidines and fused N–aromatic rings has a considerable effect on the electronic properties of these complexes. Incorporation of a pyrimidine ring facilitates the stabilisation of azo anion radicals and leads to the formation of diruthenium(II) species, bridged by radical species. The X–ray crystal structures of both these complexes were determined. The use of the hexadentate ligands coordinating in a bis–tridentate manner mediate even stronger communication between the two ruthenium centres. Ligands containing bis–pyridylimines result in weaker coupling between the metal centres in dinuclear ruthenium(II) species. A complete absence in the inter–metal communication was observed with increasing the distance and/or flexibility between the two pyridylimine units, contrary to a previous reported claim. Reaction with different silver(I) salts afforded an array of one–dimensional coordination polymers and a discrete dinuclear complex depending on the coordination strengths of the anions. The metallosupramolecular assemblies obtained were characterised mainly by X–ray crystallography, elemental analysis and mass spectrometry.

The synthesis of the catenane components, a dithiol and a cyclophane, are described using previously reported methods. 1-3 The preparation techniques used to obtain a self-assembled dithiol monolayer and a self-assembled catenane monolayer from dilute solution onto a gold's surface are also reported. Grazing angle reflectance infrared spectroscopy was used to characterize the selfassembled dithiol and catenane monolayers. The infrared spectra revealed evidence for the existence of the dithiol monolayer and possible evidence for the existence of the catenane monolayer. A catenane transmission film spectrum was obtained to provide evidence for the existence of the catenane itself. When the transmission and the monolayer spectra were compared, shifts in a few of the absorption bands revealed some association between the dithiol and the cyclophane. / Department of Chemistry

No description available.

The main subject of the thesis is the investigation of palladium-iron alloy electrodeposition from aqueous solutions in general. Palladium-iron alloy deposits could be in principle a substitute for nickel or nickel-palladium deposits to avoid metal dermatitis. Nickel contact dermatitis is an especially sensitive allergy caused by decorative or functional use of nickel: it needs to be avoided in a number of applications. Electrochemical and chemical experiments have been carried out on several solutions with variable pH, salts and metal complexes to design a chemical and electrochemical stable electrolyte for palladium-iron alloy electrodeposition. Electrochemical measurements, physical and chemical analysis techniques, mechanical, optical, chemical and electrochemical measurements methods as well as different corrosion tests were used to describe the electrochemical processes and the properties of the palladium-iron deposits. Investigations have shown that from ammoniacal electrolytes electrodeposition in a wide range of composition is possible (pH = 7.5 - 10.5). Electrolyte consists of palladiurn as Pd(NH3)4CI2 and iron as iron(ill)-citrate. Composition of the deposited alloys depends mainly on the ratio of the metal ions in the electrolyte, while the effect of current density and electrolyte temperature is slight. Current efficiency depends on iron concentration in the electrolyte and is a maximum of ca. 85 %. Palladium-iron alloys with a higher content of palladium (>80.-%) show cracks because of the high internal stress (tensile stress) of those layers. Alloys with smaller content of palladium (<20 wt. -%) are less sensitive to cracking. Wear resistance and corrosion resistance of the palladium-iron alloys are similar or sometimes better to palladium, palladium-silver, palladium-cobalt or palladium-nickel deposits. Hardness of the palladium-iron layers increases with increasing iron content from 200 to 600 VHN. Contact resistance is low in the range of 0.5 to 1.5 mfl and barrier layer properties are excellent for gold and copper diffusion during services up to 160 degrees Celsius for 240 hours.

Electrochemical ellipsometry is employed to determine the real and imaginary parts of the refractive index and the thickness of thin films as functions of the potential applied to the electrode upon which the film is grown. The relatively recent advent of an analyser with no moving parts, the Stokesmeter, has removed previous time restraints and allows microsecond resolution. The Newcastle system is extremely novel, using a Stokesmeter, and thus being capable of 325 gs resolution, and also being electrochemically interfaced. The ellipsometric studies have concentrated on the growth and behaviour of a series of electroactive polymers derived from salicylaldehydes (Salens). [Ni(SaltMe)] and [Ni(SaIdMe)] were found to yield stable homogeneous films upon polymerisation, however while the behaviour during film growth was similar, marked differences were observed during potential cycling, poly[Ni(SaIdMe)] showing a marked decrease in thickness near the anodic limit not observed for poly[Ni(Saltme)], indicating that even minor changes to ligand structure well away from the site of polymerisation may have significant effects on the resulting film. The behaviour of poly[Ni(OMeSaltMe)] during polymerisation is more complicated; initially a homogeneous film is produced, however about half way through the growth process the film becomes inhomogeneous, and remains so during subsequent potential cycling. This behaviour was also observed for poly[Pd(OMeSalen)], indicating electron donating groups around the phenyl rings of the ligand have a profound effect on the nature of the polymer films, possibly far more so than the identity of the central metal.