The following Thesis is comprised of two separate and individual parts, both of which relate to the disposal of hydrogen sulfide. Section One is an investigation into the possibility of developing a hydrogen sulfide decomposition process which would produce both hydrogen and elemental sulfur. Section Two deals with the speciation study of a catalyst used in a traditional process which converts hydrogen sulfide gas into elemental sulfur. / Section 1: <p> The disposal of hydrogen sulfide by electrolysis to produce both hydrogen and sulfur appears to an interesting alternative to the conventional Claus process which wastes the hydrogen content of hydrogen sulfide. The electrolysis at room temperature has been reported in the literature, however, the investigation was somewhat limited by the low conductivity displayed by the electrolysis solution (pyridine/hydrogen sulfide mixture). </p> <p> The primary goal of this research was to construct a suitable apparatus and carry out a series of conductivity measurements of liquid hydrogen sulfide at room temperature with and without the addition of possible electrolytes. The objective was to determine if an electrolyte could be found that would increase the conductivity to a suitably high level to warrant the further investigation of the electrolysis process. </p> <p> Of the six possible electrolytes, only tetrapropyl ammonium iodide increased the conductivity to a desirable level. A 0.4034 M solution of this alkyl ammonium iodide in liquid hydrogen sulfide increased the conductivity (at 23 C) from 7.00 X 10-8 ohm-1cm-1 for the pure solvent to 1.13 X 10-2 ohm-1cm-1. This increase was attributed to the formation of the corresponding hydrogen sulfide adduct and its subsequent dissociation in liquid hydrogen sulfide. </p> </p> Now that it has clearly been established that appropriately high conducting solutions of hydrogen sulfide can be prepared, the further investigation of the electrolysis of hydrogen sulfide as a viable industrial process is warranted. </p> Section 2: <p> This section deals with the investigation of species present in vanadium(IV): citrate solutions over a wide range of pH values. Various spectroscopic methods (UV/VIS, ESR, vanadium Sl FT-NMR) were used to probe this specific system. The accumulated spectroscopic data were rationalized on the basis of thirteen vanadium(IV) containing species, four of which were proposed to be vanadium(IV): citrate species. Based on the observed spectroscopic data an equilibrium diagram was prepared which illustrates the vanadium(IV) species present as a function of pH. </p> / Thesis / Master of Science (MSc)

In dieser Arbeit wurden die Molekülstrukturen und die elektronischen Eigenschaften von Vanadium(IV)- und Oxo-Rhenium(V)-Chelaten mit einem kombinierten molekülmechanisch-quantenchemischen Ansatz untersucht, um sterische und elektronische Effekte der Komplexierung mit einem theoretischen Modell zu quantifizieren. Es konnte gezeigt werden, daß auf diese Weise detaillierte Aussagen zu den Bindungsverhältnissen der Metallchelate getroffen werden können. Die Berechnung der Molekülstrukturen gelingt mit exzellenter Übereinstimmung mit den Kristallstrukturen der Komplexe. Die molekülmechanischen Berechnungen erfolgen auf der Grundlage des Extensible Systematic Force Field ESFF und des Consistent Force Field 91 (CFF91). Dabei konnte die hohe Flexibilität und Zuverlässigkeit des regelbasierten ESFF für eine Vielzahl verschiedenster Metallchelate nachgewiesen werden. Aufgrund der mangelhaften Ergebnisse für trigonal-prismatische Komplexgeometrien mit dem ESFF wurden eine Anpassung des CFF91 für derartige Vanadiumkomplexe vorgenommen. Auf Grundlage von theoretischen Ergebnissen wurden die alternativen Strukturen von isoelektronischen Vanadiumkomplexen berechnet und in Übereinstimmung mit experimentellen Daten, theoretischen Modellen der Komplexchemie und empirischen Fakten eine Hypothese für die Ursache der strukturellen Differenzen erarbeitet.<br> Der hier vorgestellte, kombinierte Algorithmus aus kraftfeldbasierter Geometrieoptimierung und single-point-Rechnung an diesen Strukturen ist ein zuverlässiger und relativ schneller Weg Molekülgeometrien von Metallkomplexen zu berechnen. Er kann somit zur Voraussagen von Komplexstrukturen und zur gezielten Modellierung definierter Koordinationsgeometrien verwendet werden. / In this work the molecular structures and the electronic properties of Vanadium(IV)- and Oxo-Rhenium(V)-chelates have been investigated to quantify steric and electronic effects of complexation. It has been shown, that in this way detailed insight can be gained into the bonding conditions of that metal complexes. Molecular mechanic calculations based on the Extensible Systematic Force Field (ESFF) and the Consistent Force Field 91 (CFF91) have been carried out. High flexibility and reliability of the rule based ESFF has been proven for a large variety of different metal chelates. Due to the poor ESFF-results for trigonal-prismatic complex geometries, a fit of the CFF91 for that species was done. Based on the theoretical results the alternative structure of isoelectronical vanadium(IV)- complexes have been calculated and a hypothesis on the reason for the structural differnces have been stated in accordance with experimental results, theoretical models of complex chemistry, and empirical facts. This combined approach of force field based geometry optimization and single point calculation at these structures has been proven to be a reliable and fast way to get molecular structures of metal complexes. It can be used to predict complex structures for modelling destinct coordination geometries.