Doctor of Philosophy / Department of Chemistry / Christopher J. Levy / A series of chiral symmetrical and unsymmetrical acid-functionalized Schiff-base ligands were synthesized by condensation reactions between 3-formyl salicylic acid and the two diamines (1R,2R)-cyclohexyldiamine (CHDA) and (R)-[1,1'-binapthalene]-2,2'-diamine (BINAM). The addition of a weak base (TEA) to these Schiff-bases resulted in the formation of a partially deprotonated ligand while the addition of the strong base NaOMe, resulted in fully deprotonated ligands. Complexations were carried out using metal salts of Fe(II), Co(II), Ni(II), Cu(II), Cu(I) and Zn(II). The partially deprotonated unsymmetrical Schiff-base (CHDA as the backbone), resulted almost exclusively in the formation of double-stranded helices with M helices. The fully deprotonated ligand, on the other hand, formed cubane-type structures with Fe(II), Co(II) and Ni(II) in methanol. Similar cubane-type structures were also obtained after complexation of the symmetrical CHDA-based ligands with Fe(II) and Co(II) using NaOMe in methanol. Reactions involving Cu(II) and Cu(I) salts resulted in either mono-or dinuclear salen complexes, even if the unsymmetrical Schiff-base was used as the starting ligand. This type of ligand conversion is dependent of the metal salt concentration in the reaction. Unsymmetrical Schiff-base ligands have a higher tendency to undergo conversion to their symmetrical salen analogues if the metal salt is added is much excess.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / In recent years both metal and semiconductor nanoparticles have gained the attention of many research groups because of their unique properties. Synthesizing metal and semiconductor nanoparticles with narrow size distribution, uniform shape, and good crystalline nature represents a significant challenge. Our research group has taken the synthesis procedure a step forward when we discovered that “when a polydispersed colloidal solution upon heating at or near the boiling point of the solvent in presence of excess surface active ligands, the particles evolve into a thermodynamic equilibrium size regime and this phenomenon was named “Digestive Ripening”. The ability to tune the nanoparticles size with a narrow size distribution after post - preparation in a reproducible fashion is remarkable. The current dissertation research encompasses the field of metal and semiconductor nanoparticles and the major part of the work is devoted to understand the digestive ripening of gold-dodecanethiol system, and the effect of the nature of the ligand and solvent temperature on a low melting point indium metal – digestive ripening. A noteworthy achievement of the current work is the ability to extent the digestive ripening to the semiconductor materials cadmium selenide and cadmium telluride by employing different ligands and by the use of different solvents. A diverse set of instrumental techniques is used for the characterization of both metal and semiconductor nanoparticles.

Doctor of Philosophy / Department of Chemistry / Christopher J. Levy / Stepped helical salen complexes with vanadium as the central metal were synthesized and characterized. The helicity in these complexes arise from the fused phenyl rings (phenanthryl and benz[a]anthryl) as sidearms, whereas the chirality arises from the chiral cyclohexyl diamine or binaphthyl diamine backbones. These complexes showed good yields and moderate enantioselectivity in asymmetric sulfoxidation reactions with methylphenyl sulfide as the substrate and H2O2 or cumene hydroperoxide as the oxidants. To further improve the closed nature of these complexes with a tetradentate salen ligand, we synthesized and characterized vanadium complexes with tridentate (S)-NOBIN backbone Schiff base ligands with phenanthryl and benz[a]anthryl as the sidearms. After initial catalytic study, we concluded that these catalysts are too open in nature to impose face selection during asymmetric induction. We also synthesized and characterized vanadium and titanium salan complexes. These complexes can adopt β-cis geometry, thereby making the complex “chiral at metal” and they are known for better catalysts in terms of asymmetric induction than their unreduced counterparts. However, these complexes showed better catalytic activity than their unreduced counterparts in sulfoxidation reactions with methylphenyl sulfide as the substrate and H2O2 or cumene hydroperoxide as the oxidants. We also put an effort to synthesize mixed salen complexes with vanadium as the central metal. These complexes have two different sidearms attached to one backbone unit. However, our method did not work well to produce pure mixed salen ligands. The catalysis results for mixed salen vanadium complexes are also comparable to the unreduced vanadyl salen complexes. Lastly, we synthesized and characterized new helical titanium Schiff base complexes with (S)-NOBIN backbone and phenanthryl and benz[a]anthryl sidearms. Single crystal studies showed that these complexes exist in the M helical conformation in the solid state. These complexes showed moderate activity in asymmetric aldol addition reactions between 2-methoxy propene and different aldehydes.

Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / Polyoxometalates are self-assembled metal-oxygen anionic clusters formed primarily by Mo, W and the Group V transition metals. Their structural, chemical and physical diversity have attracted much attention from fields such as catalysis, imaging, magnetic materials, medicine and photochromism. While many of these inorganic systems are easy to prepare, their conversion to hybrid inorganic-organic materials through functionalization is an ongoing challenge. Two approaches used for functionalization involve the insertion of metal-nitrido fragments into a lacunary polyoxometalate or the direct replacement of the terminal oxo ligands with the isoelectronic organoimido [NR][superscript]2-, hydrazido [NNR[subscript]2][superscript]2-, nitrosonium [NO][superscript]+ and diazenido [NNR][superscript]+ ligands. The later process has been proven successful with a variety of different nitrogenous ligands. One of our group's goals has been to synthesize a functionalized hexamolybdate species capable of metal coordination, with the ultimate goal of forming self-assembled networks. However, previous results have been unsuccessful due to the electron withdrawing effect of the cluster which is transmitted to the metal binding site. In order to overcome this effect, several new organoimido delivery reagents (phosphineimines, isocyanates and arylamines) containing electron donating substituents have been synthesized and characterized. Attempts to attach these species to hexamolybdate are described. The synthesis and characterization of biarylimido ligands bearing remote σ-donor functionalities and their incorporation into the hexamolybdate cluster will be described. A new and exciting avenue of polyoxometalate chemistry will be demonstrated through the successful metal coordination of the biarylimido functionalized hexamolybdate to a ruthenium(II) metalloporphyrin. This also brings the hexamolybdate polyoxometalate one step closer to being capable of forming the supramolecular architectures mentioned earlier. A chromium(V) nitrido polyoxometalate has been synthesized and characterized from a lacunary Keggin precursor, in collaboration with our colleagues in Paris. The ability of this complex as a nitrogen transfer reagent will be explored. An alternative synthetic route to the osmium-nitrido-Dawson species, [(OsN)P[subscript]2W[subscript]17O[subscript]61][superscript]4- will also be described. These nitrido species could be an entry point to other derivatives through reactions with various nucleophiles and electrophiles.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / Non-polar halogens (Cl2, Br2 and I2) and polar interhalogen molecules (ICl, IBr and ICl3) have been adsorbed on the surface of several high surface area materials, including three different nanosized metal oxides (NanoActive® (NA) Al2O3 Plus, NA-TiO2 and NA-CeO2). The prepared halogen and interhalogen adducts have been characterized in detail by thermogravimetric analysis (TGA), UV-Vis, Raman and X-ray photoelectron spectroscopies (XPS) and the results are discussed herein. The different metal oxides lead to varying strength of adsorption of the halogen/interhalogen in the prepared adducts and adsorption is stronger in the nanosized metal oxides as compared to their macrocrystalline available counterparts. Nanosized metal oxide halogen adducts possess high surface reactivities due to their unique surface morphologies. These adducts have been used as reactive materials against vegetative cells, such as Escherichia coli and Bacillus megaterium, as well as spores, including Bacillus subtilis and Bacillus anthracis (Δ Sterne strain). High biocidal activities against both Gram-positive and Gram-negative bacteria, as well as spores have been obtained. Bactericidal test procedures include a water suspension method and a dry membrane method and the results illustrate that good results are obtained using both procedures. Transmission electron micrographs have been used to illustrate the treated and untreated cells and spores, giving insight into the mechanism. It is proposed that the abrasive character of the particles, along with the oxidative power of the halogens/interhalogens as well as the electrostatic attraction between some of the metal oxides and the biological material are main reasons for the high biocidal activities. Three different bacteriophages (MS2, φX174 and PRD1) have also been studied and initial results indicate that there is big potential for the use of metal oxide halogen and interhalogen adducts for the destruction of viruses. Other potential uses for them also include halogenating agents in organic and inorganic synthesis as well as a safe way to store intact halogens.

Doctor of Philosophy / Department of Chemistry / Kenneth J. Klabunde / A new approach to synthesize nanosized strontium titanate (SrTiO3) and barium titanate (BaTiO3) has been developed. Nanocrystals of mixed metal oxide were synthesized by a modified aerogel procedure from alkoxides. The textural and surface characteristic properties were studied by nitrogen BET analysis, transmission electron microscopy, and powder XRD. The crystallite sizes of aerogel prepared powders can vary from 6 to 25 nm by the use of different solvents. A mixture of ethanol and toluene was found to be the best binary solvent for supercritical drying, which produced a SrTiO3 sample with a surface area of 159 m2/g and an average crystallite size of 8 nm, and a BaTiO3 sample with a surface area of 175 m2/g and an average crystallite size of 6 nm. These titanates have been studied for photocatalytic oxidation of volatile organic compounds and acetaldehyde (CH3CHO) in particular. The big band gaps of the bulk (3.2 eV for SrTiO3 and 3.1 eV for BaTiO3) limit their application to a UV light region only. The modification of titanates by doping with transition metal ions (partial substitution of Ti ions with metal ions) creates a valence band or electron donor level inside of the band gap, narrows it, and increases the visible light absorption. The enhanced adsorption of visible light was achieved by the synthesis of nanosized SrTiO3 and BaTiO3 by incorporating Cr ions during the modified aerogel procedure. Gaseous acetaldehyde photooxidation has been studied on pure SrTiO3 and BaTiO3, and on chromium doped Cr-SrTiO3 and Cr-BaTiO3 under UV and visible light irradiation, and compared with the photoactivity of P25 TiO2. SrTiO3 doped with antimony/chromium shows absorption in visible light and show photocatalytic activity for CH3CHO oxidation. The reason for the codoping of SrTiO3 with Sb/Cr was to maintain the charge balance and to suppress oxygen defects in the lattice. This photocatalyst shows high photoactivity under visible light irradiation even after several continuous runs. The photoactivity under visible and UV light irradiation was almost identical for the Sb/Cr-SrTiO3 photocatalyst. Dielectric properties of aerogel prepared barium titanate samples have being studied and the bulk resistance values of AP-BaTiO3 were significantly lower than that of commercial BaTiO3, by several orders of magnitude.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / The directed-assembly of small molecular building-blocks into discrete supermolecules or extended networks through non-covalent intermolecular interactions is an on-going challenge in the field of crystal engineering. This synthetic challenge may be overcome by identifying or establishing a hierarchy of intermolecular interactions which, in turn, may facilitate a modular supramolecular assembly process producing final products in high yields. A family of three 3-pyridine/amino-pyrimidine supramolecular reactants (SR’s) was prepared and allowed to react with aromatic carboxylic acids producing nine 1:1 molecular co-crystals and four 1:1 ionic salts through heteromeric O-H···N/N-H···O or charge-assisted N–H+···O-/N–H···O- hydrogen bonds with the amino-pyrimidine binding site. We introduced a Q-value, based on AM1 calculations, to show that the amino-pyrimidine moiety is a superior hydrogen-bond acceptor for an incoming carboxylic acid. The amino-pyrimidine/carboxylic acid synthon resulted 13/13 times (100 % yield) even in the presence of other potentially disruptive intermolecular interactions. However, reacting a 4-pyridine/amino-pyrimidine SR and a carboxylic acid in a 1:2 ratio, resulted in structures containing both acid/amino-pyrimidine and acid/pyridine synthons. The same family of pyridine/amino-pyrimidine SR’s were allowed to react with halogentated benzoic acids in which the amino-pyrimidine/carboxylic acid synthon formed 7/7 times (100 % yield) and halogen bonds (N···I or N···Br) extended the SR/acid dimers into polymeric networks 4/7 times (57 %). These results were rationalized through a hierarchial view of intermolecular interactions consisting of hydrogen and halogen bonds. Four bifunctional 3-pyridine/amino-pyrimidine or amino-pyridine SR’s were reacted with neutral metal complexes producing thirteen crystal structures in which the pyridyl moiety coordinates to the metal center 13/13 times (100 % yield) and amino-pyrimidine···amino-pyrimidine hydrogen bonds link the neighboring metal-ligand complexes 10/13 times (77 % yield) into 1-D or 2-D extended architectures. Finally, we synthesized and characterized a series of tetra-substituted hydrogen bond donor and acceptor functionalized, i.e. pyridyl, amino-pyridine, carboxylic acid, resorcinarene-based cavitands forming deep-walled cavitands through amino-pyridine···carboxylic acid heteromeric synthons and a heterodimeric molecular capsule through pyridyl···carboxylic acid hydrogen bonds. The heterodimeric capsule is only one of three, of its type, characterized crystallographically.

Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / Polyoxometalates have attracted much attention over the last few decades and have been studied in a wide variety of fields such as catalysis, medicine, imaging, photochromism, and magnetic materials. While many of these systems are easy to prepare, the ability to functionalize polyoxometalates is an ongoing challenge. Two approaches used to functionalize polyoxometalates involve insertion of metal fragments into a lacunary polyoxometalate or the direct replacement of terminal oxo ligands with the isoelectronic organoimido ligand. This process has been proven successful in many cases and with a wide variety of organoimido compounds. One of our group’s goals has been to synthesize a functionalized hexamolybdate species that is capable of metal coordination. However, previous results have been hindered because the electron withdrawing effect of the cluster is transmitted to the metal binding sites. In order to combat the electron withdrawing effect of the cluster, 4-amino piperidine dithiocarbamate ligands, which have no conjugation in the ring and are capable of metal binding, have been synthesized and characterized. A series of transition metal complexes have been made and a single crystal has been grown of a nickel(II) complex. Attempts to attach these species to clusters are described. Imido hexamolybdate clusters have been functionalized with styryl and iodophenyl groups. The styrene functionalized hexamolybdate was copolymerized with 4- chloromethylstyrene in moderate yields. This copolymer has the capabilities for further substitution at the chloromethyl group. The iodophenyl functionalized hexamolybdate was fully characterized including a single-crystal X-ray structural determination. This functionalized hexamolybdate can be used in carbon-carbon bond formation through coupling reactions. A chromium(V) nitrido polyoxometalate has been synthesized from a lacunary Keggin precursor and characterized. This nitrido species shows promise as a nitrogen transfer agent. Likewise, this nitrido species could be an entry point to other derivatives through reactions with various nucleophiles and electrophiles.

Doctor of Philosophy / Department of Chemistry / Christer B. Aakeroy / Tailoring the properties of a bulk material such as a pharmaceutical compound, through non-covalent interactions, could lead to the enhancement of its physical properties without chemically modifying the individual molecules themselves. In order to obtain a degree of control and reliability of these non-covalent interactions, we must develop a series of synthons - patterns of non-covalent interactions between molecules. A family a N-heterocyclic amides were synthesised and an assessment of their binding selectivities was made, by evaluation of the supramolecular yield, (the frequency of occurrence of the desired connectivities). It was found that the supramolecular yield increased with increasing basicity of the heterocyclic nitrogen atom. However, there is a point where the heterocycle becomes basic enough to produce salts, which often leads to unpredictable connectivity and stoichiometry. Once the effectiveness of the N-heterocyclic amides as supramolecular reagents was established, a series of more closely-related ditopic hydrogen-bond acceptor molecules were synthesized. The supramolecular reagents contained imidazole and pyridine binding sites, so that the two sites differ in terms of their basicity and geometry. An assessment of the ability of these molecules to induce selectivity when a hydrogen bond donor such as a cyanoxime or a carboxylic acid is introduced was made. A total of nineteen crystal structures were obtained, of which one yielded a salt with unpredictable connectivity, and eighteen were cocrystals. Ten of these were 2:1 co-crystals, which shows that the two sites are accessible for binding. Eight were 1:1 stoichiometry, with five out of eight (63%) forming a hydrogen bond to the best acceptor. In addition, a series of molecular electrostatic potential calculations were employed to investigate the binding preferences and probe the best donor/best acceptor hypothesis. A ternary supermolecule was also constructed from a central, asymmetric hydrogen-bond acceptor and two different hydrogen-bond donor molecules. It was found that the best donor, the cyanoxime, bound to the best acceptor, the imidazole nitrogen atom, while the second best donor, a carboxylic acid, bound to the second best acceptor. The calculated molecular electrostatic potential values were used to rationalize this event. A series of substituted cyanophenyloxime, hydrogen bond donor molecules were synthesized and their effectiveness at forming co-crystals was examined. It was found that simple R group substitution could have a significant effect upon the co-crystal forming ability of the hydrogen bond donors, having improved the yield from 4% and 7% in a series of co-crystallizations with closely-related oximes, to 96% with the cyanoximes. A series of di- and tritopic cyanoximes were synthesized and an assessment of their co-crystal-forming ability was made. They were found to be equally effective at producing co-crystals as the monotopic cyanoximes, having done so in 23 out of 24 cases. In contrast to their carboxylic acid counterparts, the polycyanoximes also exhibited excellent solubility. Finally, a series of ditopic ligands (N-heterocyclic amide and pyridyl cyanoximes) were employed in the synthesis of metal complexes. The amide-based ligands were found to be very effective at organizing the metal architectures with coordination through the heterocyclic nitrogen atom and propagation of one-dimensional chains through carboxamidecarboxamide interactions. These interactions prevailed even in the presence of potentially disruptive species such as solvent molecules, (in Ag(I) complexes) counterions, or other hydrogen bond acceptors. The self-complementarity of the oxime moiety was found not to prevail in any of the cases, but the pyridyl cyanoximes were consistent in their behaviour, forming an O-H…O (oxime-oxygen) hydrogen bond to a carboxylate or acac moiety.

Master of Science / Department of Chemistry / Kenneth J. Klabunde / In this study, low molecular weight nanocomposites of L-lactic acid were synthesized with Commercial, Nanoactive®, and Nanoactive Magnesium Oxide Plus®, each of which differs in both surface area and shape. Synthesis of the composites was carried out by refluxing the nanoparticles in a solvent suspension. Both methanol and 1-propanol were used during this work. Heating was necessary in order to achieve adequate dispersion of the particles before adding L-lactic acid. Upon addition of the lactic acid monomer, the reactants were refluxed for a total of 3 hours, followed by evaporation of the excess solvent. The products were characterized via DSC, TGA, FTIR, [superscript]1H and [superscript]13C NMR, UV-Vis, XRD, and TEM. Additionally, titrations were performed with the reactants to ensure the particles were not being consumed by the acid regardless of their size. The results of this study indicate that condensation reactions are the primary polymerization route of lactic acid and polymerization appears to initiate on the surface of the magnesium oxide particles, resulting in physically unique composites of lactic acid and magnesium oxide.