Search

This work examines the relative importance of diffusion and the electrical time constant of the working electrode on the response time of amperometric gas sensors. The response curve of an electrochemical carbon monoxide sensor to a 200 ppm CO test gas was measured as a function of the added resistance that is in series with the working electrode to increase the time constant. It has been found that the response time increases with additional resistance. The experimental behavior was compared to the values predicted on the basis of Fick's second law of diffusion and to the values expected on the basis of the electrical properties of the sensor. The behavior of the sensor was explained using an equivalent electrical circuit, describing the time constants of the working electrode. Values obtained from this model were further compared to experimental values obtained from electrochemical impedance spectra. It has been found that the response time of the sensors depends on both the rate of diffusion and the electrical time constants of the working electrode.

An analysis of the factors controlling reversible dioxygen binding in lacunar Co(II) cyclidene complexes reveal that steric and electronic methods control dioxygen affinity. The Co-O-O bond angle is sensitive to the atmosphere and reveals complex variations that depend upon ligand substituents. ESR and simulation methods characterize the dioxygen complexes.

Electrochemical, spectrophotochemical and spectroscopic techniques are capable of characterizing the reactivity of superoxide with iron II complexes. The complexes have pentadentate ligands and hexadentate ligands. Electrically conductive polymers on the electrode surface at negative potentials exist and is indicated by the repetitive cyclic voltammograms of the two complexes. The polymers are formed under aerobic conditions which are induced by hypervalent iron species.

A nonaqueous solution is used to autoxidate cobalt (II) cyclidene compounds with R3 double bonded to CH3. The fractional pressure of dioxygen influences the rate of autoxidation, ligand replacements and convergence and features of the base which is introduced. The conjugate base is formed by a method in which a preequilibrium deprotonation of the dioxygenated cobalt (II) participates. The ligand is irreversibly oxidated by the base. Quick autoxidation is caused when R2 binds to H due to an analogous deprotonation system. An increase in the insulation of the cobalt (II) compounds to the process of autoxidation is observed after the isolation of the two acidic sites.

The synthesis and characterization of cobalt(II) cyclidene complexes with long polymethylene bridges and their reactions with dioxygen were described. The crystal structure of the bis(isothiocyanate) undecamethylene-bridged cobalt(III) complex has been solved, and the effects of coordination of a small molecule within the cavity on the conformation of the ligand were examined. Moreover, the dioxygen affinities and autoxidation reactions of the long-bridged cobalt(II) complexes are compared with those of the shorter bridged cobalt(II) cyclidene complexes.

The complex (Fe DPC Cl)PF6 derived from the reaction of iron(II) chloride with 4,7-bis(2-picolyl)-4,7-diaza-1-oxacyclononane (DPC) was studied using X-ray crystallography. DPC was synthesized from the interaction between (9)-aneON2 and 2-picolyl chloride hydrochloride in water. Results showed that the newly formed complex contained a macrocyclic ring with a chloride atom attached trans to a nitrogen atom of DPC. Additional reactivity studies involving Fe(TPC)2+ were conducted to further characterize the compound's structure.