Insight into the effect of secondary interactions, fluorination, as well as substituent effects on strong ionic hydrogen bonds has been acquired through studies of FHF-, NFnH3-n•••F- (n = 0..2) and [M-H]- (M = Glycine, Alanine, Valine, Serine) clustered with ROH (R = H, CH3, C2H5). Excellent agreement was observed between thermochemical values obtained from high pressure mass spectrometry measurements and those predicted from MP2(full)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations. In the examination of the clustering of FHF-, a strong correlation between the hydrogen bond strength and the gas phase acidity of the solvent was observed. In addition, several interesting observations on various structural and thermochemical properties were made for each of the three solvents. Upon formation of clusters with water, it was found that the large entropic advantage of one particular structure, which was not the most enthalpically favored, was significant enough to make it the predominant species within the ion source. In the case of methanol solvation, no evidence of secondary interaction of the methyl group and any other moiety could be found. The structural details revealed from calculations of the ethanol-solvated clusters indicate that secondary interactions between the terminal methyl group and FHF- had an impact on the length of both the FHF and OHF bonds present. In an attempt to gain insight into the effects of fluorination on hydrogen bonding, clusters of NFnH3-n (n = 0..2) and F- have been computationally investigated. The hydrogen bond energy in NH3∙∙∙F-, NFH2∙∙∙F- and NF2H∙∙∙F- were calculated to be -67.9 kJ∙mol-1, -120.2 kJ∙mol-1 and -181.2 kJ∙mol-1, respectively, and clearly show the effect of fluorination on hydrogen bond strength in amine-fluoride systems. The change in enthalpy and entropy for the clustering of methanol to NF2H∙∙∙F- to form the fluoride bound dimer of methanol and difluoramine has been measured via high pressure mass spectrometry to be -68.3 kJ∙mol-1 and -90.5 J∙K-1∙mol-1. These values are in excellent agreement with the calculated analogues, -70.9 kJ∙mol-1 and -88.5 J∙K-1∙mol-1. Finally, an examination of the thermochemical properties associated with the formation of a hydrogen bond linkage between protic solvents and deprotonated amino acids has been performed. In addition to observations of the effect of side chain substitution, a comparison between measured and calculated properties has provided insight into the thermochemical effects arising from the isomeric nature of this clustering system. A new theoretical model describing the impact of a distribution of isomers on thermochemical measurements made via high pressure mass spectrometry is given. When this new model was applied, and the distribution of isomers correctly accounted for, the measured values of 〖∆H〗^°, 〖∆S〗^° and 〖∆G〗_298^° consistently agreed, to a very high degree of accuracy, with those predicted by MP2(full)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations. As well, IR spectra for the clustering of deprotonated glycine with ROH have been calculated and analyzed to demonstrate the ability of techniques such as IRMPD to identify the presence of a distribution of isomers.

The past decades have witnessed the development of new materials with large nonlinear optical properties, which have made them attractive candidats for a broad spectrum of breakthrough applications in the electro-optic and photonic fields (e.g., telecommunication and computing). A deeper understanding of the relationship between, on the one hand, the chemical structure and, on the other hand, the electronic and (linear and nonlinear) optical properties has proven useful for the rational design of new efficient materials. Reaching such an understanding has attracted major interest in the scientific community worldwide in both academia and industry. Therefore, the development of new efficient NLO chromophores and materials along with commercial devices of high quality is helped via the establishment of multidisciplinary research teams combining: (i) the theoretical modeling using quantum-chemical computational calculations; (ii) the organic synthesis; (iii) the optical characterization; and (iv) the device fabrication. In this dissertation, quantum-chemistry is used to evaluate the second- and third-order NLO properties of series of new chromophores and take advantage of a feedback loop with the experimental team to understand the structure-property relationships.

In recent decades, tremendous efforts have been made to obtain high hydrogen storage capacity in a stable configuration. In the literature there are plenty of experimental works investigating different materials for hydrogen storage and their storage values. In the first part of this thesis the available literature data have been collected and tabulated. In addition to the literature survey the hydrogen storage capacity of carbon nanotubes and carbon nanotubes doped with boron nitride (CBN nanotubes) with different chirality have been investigated by performing quantum chemical methods at semiempirical and DFT levels of calculations. It has been found that boron nitrite doping increases the hydrogen storage capacity of carbon nanotubes. Single wall carbon nanotubes (SWNT) can be thought as formed by warping a single graphitic layer into a cylindrical object. SWNTs attract much attention because they have unique electronic properties, very strong structure and high elastic moduli. The systems under study include the structures C(4,4), H2@C(4,4), C(7,0), C(4,0), and the BN doped C(4,4), H2@C(4,4), 2H2@C(4,4), C(7,0), H2@C(7,0), 2H2@C(7,0). Also, we have investigated adsorption and desorption of hydrogen molecules on BN doped coronene models by means of theoretical calculations.

Solid-state NMR spectroscopy is used to investigate strong hydrogen bonds in a variety of solids. NMR measurements of the 2H nuclear quadrupole coupling (CQ) and nuclear magnetic shielding tensors are performed on samples of trimethylammonium chloride (TMAC), protonated 1,8-bis(dimethylamino)napthalene (DMANH+), and potassium and sodium bifluoride. 2H CPMAS is used to obtain high quality spectra while reducing experimental time. From spectral simulations, values of 127, 36, 59 and 58 kHz are determined for the 2H CQ of TMAC, DMANH+ CF3SO3-, NaHF2 and KHF2, respectively. The 2H CPMAS spectrum of TMAC shows a minor secondary component resulting from a solid phase in which the trimethylammonium cation is experiencing precessional motion. At high temperature the 2H CPMAS spectrum of DMANH+ shows unexpected spinning sideband lineshapes because of residual dipolar coupling to 14N. The experimental 2H CQ values are corroborated by ab-initio and DFT calculations; for DMAN and the bifluorides the 2H CQ values are averaged over the potential energy surface to improve the computational quality. Large values of the isotropic chemical shift (>10 ppm) are observed for all of the hydrogen-bonded deuterons. To complement the 2H NMR work, other nuclei in the compounds of interest are investigated, for TMAC these include: 35Cl, 37Cl, 1H, 14N, 15N. The 35Cl CQ shows a small, but observable deuterium/proton isotope effect. Quadrupolar and chemical shift parameters for assorted nuclei in TMAC are calculated at various N-H distances, demonstrating the strong dependence of the chlorine and hydrogen parameters on the proton position. For DMANH+ the 15N CPMAS spectrum of a static sample of DMANH+-d1 provides a value for the average dipolar 15N-D coupling constant of 870±30 Hz, corresponding to a distance of 1.29 A. Spectra of the counterions in the bifluoride salts are obtained, providing CQ values of 123 kHz and 1.141 MHz for 39K and 23Na, respectively.

Mechanochemistry, the use of mechanical stress to activate chemical reactions, has emerged as a significant area of interest in recent years. Two theoretical approaches have been developed to simulate mechanochemical processes: COnstrained Geometries Simulate External Force (COGEF) and External Force is Explicitly Included (EFEI). In the COGEF method, mechanical stress is simulated by increasing the distance between atoms in a molecule that serve as pulling points (PPs) at a constant rate. In the EFEI methods, a constant external force (Fext) is applied between PPs, allowing the atoms to move to maintain that force. Both methods have been used in the literature to study the ring opening of cyclobutene under mechanochemical conditions. These studies have shown that applying a force between cis PPs in cyclobutene induces ring opening along the conrotatory pathway in COGEF-based simulations and ring opening along the disrotatory pathway in EFEI-based simulations. The latter is consistent with experiments. The work in this thesis identifies the origin of the differences in the outcomes obtained with these two methods, which may be of interest in the context of researchers selecting methods to simulate mechanochemical processes. The results demonstrate that the origin of the difference in behaviour is related to the manner in which these methods alter the potential energy surface (PES) through the application of a mechanical stress. Specifically, the PES obtained with the COGEF method does not contain a minimum energy pathway (MEP) linking cyclobutene to the disrotatory product, whereas the EFEI surface does contain such a path. The differences in PESs suggest that the EFEI method is more suitable to simulate mechanochemical processes. The EFEI approach was then used to examine how the electronic structure evolves to permit a formally forbidden disrotatory reaction to occur. The circumvention of the Woodward-Hoffmann rules was not due to a change in the electronic structure. Instead, the application of an external force shifts the transition state along the reaction coordinate towards the reactants, lowering the barrier for the reactions. The orbital effects that disfavor movement from reactants to products are rendered secondary to mechanochemical factors. / Thesis (Master, Chemistry) -- Queen's University, 2011-12-14 16:47:24.197

Copper-organonitrogen complexes are studied by threshold photoionization and zero electron kinetic energy photoelectron spectroscopy. These complexes are prepared in pulsed laser vaporization supersonic molecular beams. Adiabatic ionization energies of the neutral species and vibrational frequencies of the neutral and ionic complexes were measured. Metal-ligand bond dissociation energies were obtained from the theoretical calculations or the experiments. More importantly, by combining the spectroscopic measurements, quantum chemical calculations, and spectral simulations, metal-ligand bonding structures are determined for copper complexes of diamines, pyridine, diazines, aminopyridines, polypyridines, and imidazole. The Cu-ethylenediamine, -(1,3-propanediamine), and -(1,4-butenediamine) complexes have been determined to be in a hydrogen-bond stabilized monodentate configuration. However, Cu atom binds to both two nitrogens in the methyl-substituted ethylenediamines. The change of the Cu binding from the monodentate to the bidentate mode arises from the competition between copper coordination and hydrogen bonding. Although pyridine, diazines, and imidazole molecules can function as a s-donor through the nitrogen atom, a p-acceptor or p-donor through six-membered or five-membered aromatic ring, only the s bonding mode is predicted by the theory and identified by the ZEKE spectroscopy. For aminopyridine molecules, s bonding through the sp2 or sp3 hybrid electron lone pair and p bonding through the pyridine ring are possible. Yet, the s bonding through the sp2 electron donation is calculated to be the strongest, and the Cuaminopyridine complexes formed by such bonding mechanism are identified by the experiments. Moreover, monodentate Cu-(4,4'-bipyridine), bidentate Cu-(2,2'-bipyridine) and Cu-(1,10-phenanthroline), and tridentate Cu-(2,2':6',2?-terpyridine) are established to be the most stable structure and are observed by experiments. It is surprising to find that the tridendate planar structure of Cu-(2,2':6',2?-terpyridine) changes to a twisted Cs structure upon ionization.

Transition metal-aromatic hydrocarbon complexes were generated in a supersonic jet and studied by zero electron kinetic energy (ZEKE) photoelectron spectroscopy and theoretical calculations. The target metal complexes were identified using time-of-flight mass spectrometry, and their ionization thresholds were located via photoionization efficiency spectroscopy. ZEKE spectroscopy was used to measure the ionization energies and vibrational frequencies of the metal complexes. Their electronic states and corresponding molecular structures were determined by comparing the experimental spectra to quantum chemical calculations and Franck-Condon simulations. In this dissertation, the metal complexes of four different aromatic hydrocarbon ligands were studied: benzene (bz), naphthalene (np), biphenyl (bp) and 1-phenyl naphthalene (phnp). In these complexes, the metal atom or ion was determined to bind to either one or two -rings. Three different bonding schemes were observed in these complexes. A twofold bonding scheme was observed in M+/M-np (M = Sc, Y, Ti, Zr, Hf), while a sixfold bonding scheme was observed in Sc+/Sc-bz and M+/M-bz2 (M = Sc, Ti, V, Cr, Mo, W). In the metal-polyphenyl complexes (i.e. Sc-, La-, and Ti-bp and Sc-phnp), twelve-fold metal-ligand bonding occurred, sixfold to two -rings of the ligand. This twelve-fold bonding mechanism requires rotation of the -rings by ~ 42 o and bending of the -rings by 40 to 57 o to clamp the metal atom or ion between the two -surfaces. Although the ground state spin multiplicities of the bare metal atoms and ions varied quite extensively, the multiplicities of the metal complexes were determined to be either singlet or doublet, except for Sc+/Sc-bz, V+-bz2, Ti-np, and Zr-np, where the triplet or quartet spin multiplicities were favored. The low spin and relatively narrower range of electron-spin multiplicities in the complexes were the result of d orbital splitting, where the degeneracy of the d orbitals was broken. Thus, the valence electrons were paired in each metal d-based molecular orbital of the complex to form low-spin singlet or doublet spin states. Some complexes favored triplet and quartet multiplicities, because the energy difference between the two highest occupied molecular orbitals was smaller than the electron pairing energy.

The reaction mechanism for the Selective Catalytic Reduction (SCR) of NO by NH3 on V2O5 surface was simulated by means of density functional theory (DFT) calculations performed at B3LYP/6-31G** level. As the initiation reaction, ammonia activation on V2O5 was investigated. Coordinate driving calculations showed that ammonia is adsorbed on Br&oslash / nsted acidic V-OH site as NH4 + species by a nonactivated process with a relative energy of -23.6kcal/mol. Vibration frequencies were calculated as 1421, 1650, 2857 and 2900cm-1 for the optimized geometry, in agreement with the experimental literature. Transition state with a relative energy of -17.1kcal/mol was also obtained. At the end of the Lewis acidic ammonia interaction calculations, it was observed that ammonia is hardly adsorbed on the surface. Therefore, it is concluded that the SCR reaction is initiated more favorably by the Br&oslash / nsted acidic ammonia adsorption. As the second step of the SCR reaction, NO interaction with the preadsorbed NH4 + species was investigated. Accordingly, NO interaction results in the formation of gas phase NH2NO molecule with a relative energy difference of 6.4kcal/mol. For the rest of the reaction sequence, gas phase decomposition of NH2NO was considered. Firstly, one of the hydrogen atoms of NH2NO migrates to oxygen. It then isomerizes in the second step. After that, the reaction proceeds with the isomerization of the other hydrogen. Finally, a second hydrogen atom migration to the oxygen leads to the formation of N2 and H2O. Total relative energy for this reaction series was obtained as -60.12kcal/mol, in agreement with the literature.

Durch diese Arbeit konnten einerseits neuartige sowie bereits bekannte molekulare Tellurringe in Clusterverbindungen und quasi-eindimensionalen Koordinationspolymeren erhalten werden. Die Stabilisierung der zyklischen, homonuklearen Einheiten erfolgt dabei stets durch die Koordination an elektronenreiche Übergangsmetallatome, wobei die koordinierenden Telluratome gegenüber diesen als Zwei-Elektronendonoren fungieren. Die molekularen Clusterverbindungen [M(Te10)](TeX4)2(TeX3)2 (M = Rh, Ir X = Cl, Br) sowie [Ru2(Te10)](TeI4)2(TeI2)2 beinhalten eine übergangsmetallstabilisierte, neutrale Te10-Einheit, wobei jedes Übergangsmetallatom zusätzlich zwei terminale Halogenidotelluratliganden koordiniert. Im neuartigen, zehngliedrigen (Te04Te+0,54Te2)-Fragment finden sich zwei nahezu linear umgebende Telluratome, die als "Tellurbrücke", zwei gefaltete Te4-Ringe zur Vervollständigung der tricyclo[5.1.1.13;5]-Einheit koordinieren. Die Bindungssituation der nahezu linearen Te3-Sequenzen im homonuklearen Fragment sowie die [X-Te-X]-Sequenzen der Halogenidotelluratliganden lassen sich mit 3c4e-Bindungen verstehen. Anhand quantenchemischer Rechnungen konnte die Mehrzentrenbindung sowie die Aussage eines übergangsmetallstabilisierten Fragments bestätigt werden. In den inkommensurabel modulierten Kristallstrukturen (M2Te14I12)(TeI4) Te2I2) (M = Rh, Ir) existieren hingegen zweifach positiv geladene (M2Te14I12)2+-Cluster (M = Rh, Ir) neben nahezu planaren Schichten bestehend aus (TeI4)2--Gruppen und (Te2I2) Molekülen. Das (Te+I2I2) Molekül konnte anhand quantenchemischer Rechnungen als stabiles Molekül in der Gasphase bestätigt werden und stellt ein schweres Homologes des S2Cl2 dar. Die quaternäre Verbindung (Ir2Te14Br12)2(InBr4)2 enthält ebenfalls einen zweifach positiv geladenen Cluster, {[Ir3+2(Te0)4(Te+0,5)4(Te-)2]Te2+2Br-6)2}2+, dessen Ladung durch zwei einfach negativ geladene (In3+Br4)--Gruppen ausgeglichen wird sowie einem neutralen Cluster, [Ir3+2(Te0)4(Te3.-)2](Te2+2Br-6)2, mit einem Te3.--Radikalanion, dessen Existenz mittels ESR-Spektroskopie nachgewiesen wurde. Die aus diskreten Molekülen aufgebaute Verbindung [Ru2(Te6)]TeBr3)4(TeBr2)2 kann je nach Betrachtungsweise entweder als Te6-Ring, der durch zwei (Ru2+Te2+3Br-8)-Kappen umgeben ist oder als [Ru2Te6]4+-Heterokuban, welcher zusätzlich mit Bromidotelluratliganden koordiniert ist, beschrieben werden. In den Kristallstrukturen der ternären Koordinationspolymere [M(Te6)]X3 (M = Rh, Ir; X = Cl, Br, I) verlaufen entlang der c-Achse lineare, positiv geladene [M(Te6)]3+-Ketten (M = Rh,Ir), in denen abwechselnd ein ektronenreiches Übergangsmetallatom und sechsgliedrige Tellurringe koordinativ gebunden sind, wodurch eine hoch symmetrische Anordnung realisiert wird. Dabei zeigt sich aufgrund der starken Bindung an die Übergangsmetallatome eine erhebliche Ringspannung im Vergleich zu den bekannten sechsgliedrigen Tellureinheiten. Isolierte Halogenidionen, welche sich in der Ebene der Übergangsmetallatome befinden, dienen einerseits zum Ladungsausgleich der positiv geladenen Ketten und verbrücken andererseits innerhalb eines Stranges benachbarte Te6-Ringe. Im Koordinationspolymer [Ru(Te8)]Cl2 konnte ein neutraler Te8-Ring mit einer bislang für achtgliedrige Chalkogenmoleküle unbekannten Konformation röntgenographisch nachgewiesen werden. Die Abweichung von der bevorzugten Kronenform, ist wiederum ein E ekt der starken Bindung zwischen den Telluratomen und den Rutheniumatomen. In den linearen, positiv geladenen [Ru(Te8)]2+-Strängen binden 3+3 Telluratome an zwei benachbarte Rutheniumatome. Isolierte Chlorid-Ionen, die zwischen den positiven Strängen eingelagert sind, dienen in der Kristallstruktur zum Ladungsausgleich. Das quaternäre Koordinationspolymer [Ru(Te9)](InCl4)2 beinhaltet eine neuartige, zyklische Te9-Einheit, welche die Vielfalt der tellurreichen Ringstrukturen erweitert. Analog zum ternären Koordinationspolymer [Ru(Te8)]Cl2 gliedert sich die Kristallstruktur in [Ru(Te9)]2+-Stränge, die entlang der c-Achse verlaufen, und dem komplexen Anion (InCl4)-. Ein besonders interessantes Strukturmerkmal der positiv geladenen Stränge stellt das käfigartige Fragment [Ru-(Te9)-Ru] dar, dessen hexazyklischer Aufbau aus kondensierten Fünfringen den isolierten Undecapniktiden Pn113- (Pn = P, As, Sb) topologisch äquivalent ist. Für einen genaueren Einblick in die chemische Bindung der tellurreichen Koordinationspolymere [Rh(Te6)]Cl3, [Ru(Te8)]Cl2 und [Ru(Te9)](InCl4)2 wurden quantenchemische Rechnungen durchgeführt. Eine topologische Analyse der Elektronendichte und des Elektronenlokalisierbarkeitsindikators (ELI-D) an koordinierenden und freien Tellurmolekülen sollte zu detaillierten Aussagen über Gründe der extremen Ringspannung aufgrund der Koordination führen. Zusammenfassend kann feststellt werden, dass die Verzerrung der Tellurringe in den Koordinationspolymeren einerseits der gerichteten Bindung zu den Übergangsmetallatomen geschuldet ist und andererseits um Platz für die sich abstoßenden freien Elektronenpaare zu bekommen. Für weitere Arbeiten könnten zunächst einerseits die Untersuchungen zur Löslichkeit der Clusterverbindung Re4Q4(TeCl2)4Cl8 (Q = S, Se, Te) in organischen Lösungsmitteln als Ausgangspunkt für die Austauschreaktionen der terminalen Halogenidotelluratliganden durch neue verbrückenden Gruppen von Interesse sein. Andererseits kann auch innerhalb des untersuchten Systems, durch Variation der Eduktzusammensetzung, neuartige Tellurmoleküle erwartet sowie die bereits erworbenen Erkenntnisse zur Übertragung auf das leichtere Homologon Selen genutzt werden.

Force field methods are used to investigate the properties of a wide variety of chemical systems on a routine basis. The expression for the electrostatic energy typically does not take into account the anisotropic nature of the atomic electron distribution or the dependence of that distribution on the system geometry. This has been suggested as a cause of the failure of force field methods to reliably predict the behaviour of chemical systems. A method for incorporation of anisotropy and polarisation is described in this work. Anisotropy is modelled by the inclusion of multipole moments centred at atoms whose values are determined by application of the methods of Quantum Chemical Topology. Polarisation, the dependence of the electron distribution on system geometry, is modelled by training machine learning models to predict atomic multipole moments from knowledge of the nuclear positions of a system. The resulting electrostatic method can be implemented for any chemical system. An application to progressively more complex systems is reported, including small organic molecules and larger molecules of biological importance. The accuracy of the method is rigorously assessed by comparison of its predictions to exact interaction energy values. A procedure for generating transferable atomic multipole moment models is defined and tested. The electrostatic method can be combined with the empirical expressions used in force field calculations to describe total system energies by fitting parameters against ab initio conformational energies. Derivatives of the energy are given and the resulting multipolar polarisable force field can be used to perform geometry optimisation calculations. Future applications to conformational searching and problems requiring dynamic descriptions of a system are feasible.