Yes / The syntheses of three series of complexes designed with self-complementary motifs for formation of halogen bonds between an iodotetrafluorophenyl ligand and a halide ligand at square-planar nickel are reported, allowing structural comparisons of halogen bonding between all four halides C6F4I⋯X–Ni (X = F, Cl, Br, I). In the series trans-[NiX(2,3,5,6-C6F4I)(PEt3)2] 1pX and trans-[NiX(2,3,4,5-C6F4I)(PEt3)2] (X = F, Cl, Br, I) 1oX, the iodine substituent on the benzene ring was positioned para and ortho to the metal, respectively. The phosphine substituents were varied in the series, trans-[NiX(2,3,5,6-C6F4I)(PEt2Ph)2] (X = F, I) 2pX. Crystal structures were obtained for the complete series 1pX, and for 1oF, 1oCl, 1oI and 2pI. All these complexes exhibited halogen bonds in the solid state, of which 1pF exhibited unique characteristics with a linear chain, the shortest halogen bond d(C6F4I⋯F–Ni) = 2.655(5) Å and the greatest reduction in halogen bond distance (I⋯F) compared to the sum of the Bondi van der Waals radii, 23%. The remaining complexes form zig-zag chains of halogen bonds with distances also reduced with respect to the sum of the van der Waals radii. The magnitude of the reductions follow the pattern F > Cl ∼ Br > I, 1pX > 1oX, consistent with the halogen bond strength following the same order. The variation in the I⋯X–Ni angles is consistent with the anisotropic charge distribution of the halide ligand. The temperature dependence of the X-ray structure of 1pF revealed a reduction in halogen bond distance of 0.055(7) Å on cooling from 240 to 111 K. Comparison of three polymorphs of 1oI shows that the halogen bond geometry may be altered significantly by the crystalline environment. The effect of the halogen bond on the 19F NMR chemical shift in the solid state is demonstrated by comparison of the magic-angle spinning NMR spectra of 1pF and 1oF with that of a complex incapable of halogen bond formation, trans-[NiF(C6F5)(PEt3)2] 3F. Halogen bonding causes deshielding of δiso in the component of the tensor perpendicular to the nickel coordination plane. The results demonstrate the potential of fluoride ligands for formation of halogen bonds in supramolecular structures. / We acknowledge an Overseas Research Scholarship from the University of York to VT. We also acknowledge support from EPSRC (grants EP/J012955/1 and EP/ J012998/1).

No description available.

<div>Polyamide based reverse osmosis (PA-RO) membranes are applied for the desalination of halide-containing waters such as seawater and brackish groundwater. They are the industry standard because of their high selectivity and ability to withstand a wide range of pH. However, one of their pitfalls is their propensity to undergo biofouling, which is deterioration due to biological growth. Biofouling is known to dramatically decrease membrane performance and increase energy consumption. In order to overcome biofouling, a disinfectant, typically free chlorine, is applied; however, free chlorine is known to react with the polyamide layer and result in further membrane deterioration and performance loss.<br></div><div>One topic that has garnered less attention is the application of chloramines and their interactions with the PA-RO membrane when applied as a biofouling control. Furthermore, the role of halides (e.g. chloride, bromide, and iodide) in the presence of chloramines must be further explored because they are known to react to form secondary species which are reactive toward PA-RO membranes. In Chapter 2, the PA based monomers benzanilide (BA) and N-Methyl-N-phenylbenzamide (N-CH₃-BA) were used to model the PA layer. Monomers were exposed to halide containing waters and chloraminated with pre-formed NH₂Cl over a wide range of pH. The decay and by-product formation after exposure were evaluated using HPLC-DAD, LC/MS, and/or GC/MS. Results indicated that pH of the system and bromide concentration controlled parent compound decay and brominated by-product formation, where low pH and high bromide concentrations led to the highest formation of brominated by-products.</div><div>In Chapter 3, commercially made PA-RO membranes (SWC4-LD) were chloraminated or chlorinated with and without halides over a wide pH range. Their performance was evaluated after exposure through flux experiments using a dead-end flow cell. Results indicated that exposure to free chlorine led to the greatest change in flux and monochloramine resulted in the smallest change in flux. During chloramination of the membranes, the reactors containing bromide led to further change in flux than the chloramine only conditions. This was likely due to formation of secondary species that were reactive toward the PA membrane. Furthermore, Chapter 4 summarizes overall research contributions from this work and proposes future work pertaining to this topic.</div>

Com base em trabalhos tanto teóricos como experimentais, tem-se concluído que o Cu+ fica em posição fora de centro em alguns halogenetos alcalinos. Neste, trabalho apresentamos resultados obtidos por técnicas de correntes termoestimuladas(ITC), para, verificar propriedades de dipolos elétricos devido a Íons de Cu+ em posição fora da centro em cristais de KCl. Ampliou-se o estudo do comportamento do Cu+ em cristais de KBr e KI. As bandas de ITC observadas nestes cristais, apresentam máximos em 62, 70 e 83 &#176K, e as energias de ativação são de 0.177, 0.196 e 0.232 eV em KCl, KBr e KI, respectivamente. A partir da integração das bandas de ITC e as concentrações de Cu+ achados por absorção ótica, o momento, dipolar elétrico é determinado, conduzindo a valores de 1.5, 1.9 e 2.6 e &#197 no KCl, KBr e KI, respectivamente. Dada a forma da banda de ITC, comprova-se que a reorientação dos dipo1os segue o modelo clássico com um tempo de relaxação simples, e que o Cu+ fica congelado em posição fora de centro abaixo daquelas temperaturas em que ocorre o máximo da banda de ITC. / Theoretical and experimental investigations have concluded that Cu+ occupies an off-canter position in several alkali halides. In this work we report results obtained by ionic thermal-currents technique (ITC) to verify the electric dipole properties due to Cu+ ions in off-center position in KC1 crystals. This was developed to study the Cu+ ion behaviour in KBr and KI crystals. The ITC band observed in these crystals geve maxima at 62, 70 and 83 &#176K, and the activation energies were 0.177, 0.196 end 0.232 eV in KCI, KBr and KI, respectively. From the integration of the ITC bands and the concentration of Cu+ obtained by optical absorption, the dipole moment is determined, giving values of 1.5, 1.9 and 2.6 e &#197 in KC1, KBr and KI, respectively. Due to the shape of the ITC band, we conclude that the dipole reorientation follows the classical model with a single relaxation time, and that the Cu+ freeze in off-center position below those temperatures where maximum occur at the ITC band.

Estudamos as propriedades de absorção e emissão de aglomerados Yb2+/CN- em haletos de potássio (KCl, KBr e KI) e estamos propondo um modelo para a estrutura geométrica do aglomerado. Neste modelo o itérbio divalente e o íon cianeto substituem um cátion e um ânion vizinhos, respectivamente, com o eixo que une os dois íons na direção . O acoplamento entre os dois impede o movimento rotacional do cianeto, mesmo à temperatura ambiente, como pode ser comprovado pela presença de linhas estreitas no espectro de absorção infravermelha. Os espectros de absorção visível e ultravioleta são compatíveis com as transições 4&#40214&#8594 4&#40213 5d do itérbio em simetria C4v. A absorção vibracional indica a presença não intencional de OCN- que pode formar aglomerados com os íons cianeto. À temperatura do nitrogênio líquido, observa-se a influência do itérbio sobre os estados rotacionais do cianeto, uma indicação da interação entre centros vizinhos. A excitação sobre as bandas de absorção ultravioleta e visível produz intensa emissão em que podem ser identificadas três regiões (450&#8594;500 nm, 500&#8594;600 nm e acima de 600 nm) com comportamentos distintos quanto à variação da temperatura e excitação. Os tempos de vida variam de 50&#181s à temperatura ambiente até 20 ms à temperatura do hélio líquido. Simultaneamente à emissão visível, observa-se a emissão vibracional-rotacional dos íons cianeto, com indicações de transferência de energia entre os íons cianeto acoplados ao itérbio e os isolados / We have studied the absorption and emission properties of the Yb2+/CN- in potassium halides (KCl, KBr and KI) and it was proposed a structural model for this system. In this model the divalent ytterbium and the cyanide ion substitute a neighboured cation and an anion along a direction. The rotational motion of the cyanide ion is constrained by the coupling with the ytterbium, which is by the presence of narrow lines in the infrared absorption spectra, even at room temperature. The UV and visible absorption spectra are compatibles with the 4&#40214&#8594 4&#40213 5d ytterbium transitions under C4v symmetry. The vibrational absorption reveals the unintentional presence of OCN- that can form clusters with cyanide ions. The influence of the ytterbium over the rotational states of cyanide can be observed at liquid nitrogen temperature, revealing the interaction between both impurities. The optical excitation if the absorption bands shows a broad and strong emission in three regions (450&#8594;500 nm, 500&#8594;600 nm and above 600 nm) with different behaviors under temperature and excitation pump changes. Lifetimes between &#181s at room temperature and 20 ms at liquid heliurn temperature can be observed. Simultaneously to the visible emission, it was observed the vibrational-rotational emission of CN- ions with evidences of energy transfer between coupled Yb<sup<2+/CN- pairs and isolated CN- ions

A montagem de um sistema que permite a detecção de modulação no coeficiente de absorção ótica, devido ao campo elétrico aplicado, foi concluída. A máxima sensibilidade atingida foi de &#916 K / K = 1,5 x 10-6 com resolução em comprimento de onda de 3 nm. O efeito Stark de 2&#170 ordem, na freqüência dupla da do campo elétrico aplicado foi medido para o centro F em KCl e KBr e comparado com provisões teóricas. Os valores obtidos para o KCl coincidem com os de Chiarotti, o que confirma o bom funcionamento do sistema, e diferem dos valores calculados teoricamente. Essa diferença é atribuída à correção do campo local. Os valores obtidos experimentalmente para a variação relativa do coeficiente de absorção foram: para KCl: &#916K / K = 2,93 x 10-5 (78&#176 K) para KBr: &#916K / K = 2,85 x 10-5 (78&#176 K) / The assembly of a system which allows the detection of modulation in the coefficient of optical absorption, due to the applied electrical field, was completed. The maximum sensitivity achieve was &#916 K / K = 1,5 x 10-6, in wave length, of 3 nm. The Stark effect of second order, in the frequency twice as that of the applied electrical field was measured for the center F in KCl and KBr and compared with theoretical previsions. The values obtained for KCl coincide with those of Chiarotti\'s, which confirms the good functioning of the system, and differ from the values calculated theoretically. This difference in ascribed to the correction of the local field. for KCl: &#916K / K = 2,93 x 10-5 (78&#176 K) for KBr: &#916K / K = 2,85 x 10-5 (78&#176 K).

<p>Organic nitrogen compounds are important in environmental systems because they are prevalent in natural waters but are also components of polymers within membrane filters that are used for water treatment. In both of these cases, these compounds can be exposed to free chlorine during disinfection, which can trigger a set of reactions that can form a host of different halogenated by-products. When such by-products form during water treatment disinfection, these by-products, known as nitrogen-based disinfection by-products (N-DBPs), can be highly toxic and affect human and ecosystem health. Alternatively, when such reactions occur during membrane filtration, the organic nitrogen compounds, which are embedded within the upper layer polymer structure of the membrane filter, can degrade when free chlorine is applied. Therefore, this research was aimed at exploring the chemistry behind how specific types of organic nitrogen compounds which are found in these applications, such as tertiary amines and amides, react with free chlorine. It particularly focused on assessing the kinetics and by-product formation of these reactions under variable water quality conditions (e.g., pH, halide concentrations, and precursor doses).</p> <p> </p> <p>More specifically, in the first phase of this work, the roles of tertiary amines in enhancing disinfection by-product (DBP) formation, such as trihalomethanes (THMs) and haloacetic acids (HAAs), during chlorination of aromatic compounds were studied. The results indicated that in synthetic solutions, chloroform (CHCl₃) and trichloroacetic acid (TCAA) were enhanced by up to 20× with tertiary amines at low dose ([tertiary amine]₀ = 0.5×[aromatic compound]₀). The enhancement effect was also dependent on the aromatic compound type, tertiary amine type and dose, and water conditions such as pH and bromide concentrations. Thus, THMs and HAAs were predicted to be enhanced when the aromatic compound reacted with R₃N-X⁺ (X=Br or Cl) and was not outcompeted by aromatic compound or tertiary amine reaction with free chlorine or bromine alone. In the second phase of this work, the reaction kinetics, by-product formation, and overall mechanisms of a polyamide-based monomer with chlorine were evaluated under varying water conditions. The current known mechanism, Orton Rearrangement, was reevaluated, and new mechanisms were proposed, where it was found that N-halogenation and ring halogenation were two independent pathways. The ability to choose either pathway was highly dependent on the water quality condition of the aqueous solution. The roles of different chlorinating/brominating agents were also investigated where certain species-specific rate constants were obtained. For the N-halogenation pathway, only chlorination and no bromination occurred in which the reactivity of the chlorinating agents likely decreased such that ClO^->HOCl. However, for the ring halogenation pathway, both chlorination and bromination occurred in which the reactivity of the chlorinating and brominating agents decreased such that Cl₂ >HOCl, and BrCl > BrOCl > Br₂ > Br₂O > HOBr, respectively. Overall, this study suggests that a number of unique reactions can occur for various types of organic nitrogen compounds which: (i) allow them to affect water quality by enhancing DBP formation, (ii) but, when integrated into a polymer matrix used for water treatment, can induce reactions that lead to permanent structural damage of the polymer. In all cases, the extent of these reactions is strongly governed by the surrounding water matrix.</p>

Graduation date: 1997

Nanolithography is a rapidly evolving field that requires new combinations of techniques to improve patterning and to assist in fabricating electromechanical devices. An increasing number of applications require surfaces with defined regions of different chemical functionality. In our previous project optimum conditions for lithographic patterning were determined and potential blockers were identified to reduce force on the tip. This work is focused on identifying good chemical modifications that will allow better control of basic patterning and to investigate the minimum force of patterning required while using each chemical system. The primary aim is to gain better control of basic pattern techniques in order to create more intricate patterns such as interdigitated arrays, which can subsequently be used in sensors. An atomic force microscope (AFM) is used to pattern the prepared colloid-coated glass slides. Several compounds were used in the investigation, including sodium sulphate, potassium sulphate, magnesium sulphate, sodium fluoride, sodium chloride, sodium bromide, and sodium iodide, potassium chloride, potassium bromide, potassium iodide, potassium dihydrogen phosphate, and potassium hydrogen phosphate. In Summary, the following were found as a result of this work:  The groups of sulphates were determined to require minimum patterning forces as indicated. Sodium sulphate took a force of 49 n Potassium sulphate took a force of 45 nN Magnesium sulphate took a force of 744.4 nN  The group of sodium and potassium halides were determined the minimum patterning forces as indicated. Sodium fluoride took a force of 8.42 nN Sodium chloride and potassium chloride took a force of 20.19 and 61.9nN Sodium bromide and potassium bromide took a force of 601.4 nN and 37.2 nN, respectively Sodium iodide and potassium iodide took a force of 953.7 nN and 47.2 nN, respectively  The phosphates were determined to require the minimum patterning forces as indicated. Potassium hydrogen phosphate took a force of 25nN Potassium dihydrogen phosphate took a force of 43 nN

Thesis (Ph. D.)--Institute of Paper Chemistry, 1961. / Includes bibliographical references (p. 85-86).