Binary element-hydride systems have become a pertinent topic for high pressure research, following the measurement of record high temperature superconductivity in the dense hydrogen-sulfur system. The experimental study followed predictions of superconductivity with high transition temperature (Tc) in (H2S)2H2 at high pressures, leading to the current consensus that the high Tc phase is H3S, produced from the decomposition and recombination of H2S at high pressures. However, conjecture over the behaviour of hydrogen sulfide upon compression, and experimental limitations, cast significant ambiguity over interpretations of the structure and mechanism of the superconducting phase. Nonetheless, theory also predicts high Tc superconductivity in the dense hydrogen selenide and telenide systems; both experimentally uncharted at high pressures prior to this study. This thesis explores and maps the phase diagrams of hydrogen-chalcogen (S, Se, Te) systems using a combination of high pressure Raman spectroscopy and x-ray diffraction techniques. Gaining a comprehensive understanding of the behaviour of these systems under pressure is crucial to the eventual elucidation of the true nature of high Tc superconductivity. Hydrogen sulfide (H2S) and hydrogen selenide (H2Se) are appreciably toxic. A simple in situ synthesis technique is reported for producing hydrogen-chalcogenides directly from their constituent elements within diamond anvil cells, circumventing the need to condense toxic gases. This technique is also utilised to provide excess hydrogen, in order to produce the hydrogen-rich cocrystals thought to be vital to the formation of the high Tc phase. The hydrogen-sulfur system is most thoroughly investigated, and first presented. High quality Raman spectroscopic data provides an experimental review of pure H2S. Studies of (H2S)2H2 evaluate the current known ambient temperature phases and reveal three novel low temperature phases. Phase II0 is identified on cooling of phase I to 173 K (10 GPa), via splitting of both the single S-H stretching mode and low-frequency H2 vibron; sharp stretching modes indicate a significant reduction in orientational disorder. Successive splitting of the low-frequency H2 vibrons indicates two additional phase changes at 29 GPa (phase III0) and 53 GPa (phase- IV0) respectively, at 80 K. Phase IV0 is associated with an overall increase in symmetry. Evidence is also presented for a tentative fourth novel low temperature phase at ~160 GPa (20 K) and for the formation of an exceptionally stable hydrogen-sulfur compound with potentially novel stoichiometry. The behaviour of the H2S and (H2S)2H2 mixed molecular system is also reported; demonstrating that the coexistence of (H2S)2H2 and H2S can influence the hydrogen-bonding within both systems at high pressures. The first high pressure studies of the hydrogen-selenium system at ambient temperature are reported. The high pressure phase sequence of H2Se (I { I0 - IV) is identified by Raman spectroscopy, mirroring that of H2S. The isothermal boundaries for phases I0 and IV are found at 7 and 12 GPa respectively, at 300 K. Phase IV may have higher symmetry than phase IV H2S. X-ray diffraction and Raman spectroscopy demonstrate that the H2Se:H2 mixtures form cocrystals of (H2Se)2H2 from 4.2 GPa, with tetragonal space group I4=mcm, analogous to (H2S)2H2. Both H2Se and (H2Se)2H2 are shown to decompose into their constituent elements above 24 GPa. Attempts to synthesise the elusive H2Te directly from hydrogen and tellurium are reported. No reaction occurs upon heating Te in H2 at 0.2 GPa to 573 K. No visible reaction occurs between H2 and the high-pressure phases of Te, upon laser-heating. No photoreaction occurs upon exposure of tellurium in hydrogen to intense laser light (532 nm) at 0.2 GPa and 300 K, but formation may be stabilised at lower temperatures.

It is widely accepted that the sharing of electrons constitutes a bond. Conversely, molecular interactions that do not involve electron transfer, such as van der Waals forces and electrostatics are defined as "non-bonding" or "non-covalent" interactions. More recently computational and experimental observations have shown situations where the division between "bonding" and "non-bonding" interactions is blurred. One such class of interactions are known as σ-hole interactions. Chapter 1 provides a literature review of investigations into the nature of σ-hole interactions, highlighting the individual contributing factors. Chapter 2 provides a detailed analysis into the nature of chalcogen-bonding interactions. Synthetic molecular balances are employed for experimental measurements of conformational free energies in different solvents, facilitating a detailed examination of the energetics and associated solvent and substituent effects on chalcogen-bonding interactions. The chalcogen-bonding interactions examined were found to have surprisingly little solvent dependence. The independence of the conformational free energies on solvent polarity, polarisability and H-bond characteristics showed that electrostatic, solvophobic or dispersion forces were not dominant factors in accounting for the experimentally observed trends. A molecular orbital analysis provided a quantitative relationship between the experimental free energies and the molecular orbital energies, which was consistent with chalcogen-bonding interactions being dominated by an n→σ* orbital delocalisation. Chapters 3 and 4 both use the molecular orbital modelling approach established in Chapter 2 to investigate the potential partial covalency in H-bonding and carbonyl···carbonyl interactions. H-bonding is generally considered to be an electrostatically dominated interaction. However, computational results have suggested a partial covalent character in H-bonding. The molecular orbital analysis revealed an n→σ* electron delocalisation in all H-bonding systems evaluated. However, no quantitative correlation could be found with experimental free energies. Similarly, the nature of carbonyl···carbonyl interactions has been subject to debate, with electrostatic or an n→π* electron delocalisation having been proposed as the dominant factors. The molecular orbital analysis employed here showed that n→π* delocalisation was exceptionally geometry dependent. Studies of literature systems reveal that n→π* delocalisation contributes to overall stability of a range of systems, with a quantitative link between molecular orbital energy and conformational free energies.

The thesis entitled “Unravelling the Nature of Halogen and Chalcogen Intermolecular Interactions by Charge Density Analysis" consists of five chapters. A basic introductory section describes the topics relevant to the work and the methods and techniques utilized. The main focus of the present work is to characterize the interaction patterns devoid of strong classical hydrogen bonds. The case studies include halogen bonds and hydrogen bonds involving bromine (as a halogen bond donor and hydrogen bond acceptor), intermolecular chalcogen bond formation involving sulphur, type I Br Br contacts, type II F F and F S interactions and S-H S hydrogen bonds. Chapter 1 discusses experimental and theoretical charge density analyses on 2,2-dibromo-2,3-dihydroinden-1-one which has been carried out to quantify the topological features of a short C Br···O halogen bond with nearly linear geometry (2.922Å, C Br···O=172.7) and to assess the strength of the interactions using the topological features of the electron density. The electrostatic potential map indicates the presence of the “- hole” on bromine while the interaction energy is comparable to that of a moderate O-H O hydrogen bond. In addition, the energetic contribution of C-H···Br interaction is demonstrated to be on par with that of the C-Br···O halogen bond in stabilizing the crystal structure. Chapter 2 discusses an organic solid, 4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole that has been designed to serve as an illustrative example to quantitatively evaluate the relative merits of halogen and chalcogen bonding in terms of charge density features. The compound displays two polymorphic modifications, one crystall zing in a non-centrosymmetric space group (Z =1) and the other in a centrosymmetric space group with two molecules in the asymmetric unit (=2). Topological analysis based on QTAIM clearly brings out the dominance of chalcogen bond over the halogen bond along with an indication that halogen bonds are more directional compared to chalcogen bonds. The cohesive energies calculated with the absence of both strong and weak hydrogen bonds as well as stacking interaction are indicative of the stabilities associated with the polymorphic forms. Chapter 3 discusses the role of a type I C-Br Br-C contact and what drives the contact i.e. how a dispersive interaction is stabilized by the remaining contacts in the structure. In the process we observe the role the Br2Cl motif which is quite unique in its nature. Also the role of the bromine atoms in stabilizing the stacking interactions has been shown by the electrostatic potentials which are oriented perpendicular to the plane of the benzene ring. Chapter 4 discusses the enigmatic type II C-F F-C and C-FS-C interactions in pentafluorophenyl 2,2- bithiazole. Both the interactions are shown to be realistic “-hole” interactions based on high resolution X-ray charge density analysis. As fluorine is the most electronegative element, its participation in halogen bonding wherein the electrostatic potential around the atom gets redistributed to form regions of electron depletion and accumulation had time and again been speculated but never observed. In this chapter the experimental charge dnsity analysis clearly identifies the “-hole” on fluorine and distinguishes the C-F S-C interaction as a halogen bond rather than the chalcogen bond. Chapter 5 discusses the experimental charge density analysis of the hitherto unexplored S-H S hydrogen bond in crystal structures. The work highlights how relatively small is the number of crystal structures which are constructed by the S-H S hydrogen bond compared to the X-H S hydrogen bond via Cambridge Structural Database (CSD) analysis. The potential S-H S hydrogen bond is studied in three isomeric mercaptobenzoic acids with experimental charge density collected on 2-mercaptobenzoic acid and theoretical estimates made on 3- and 4-mercaptobenzoic acid. The strength and directionality of the S-H S hydrogen bond is demonstrated to be mainly due to the conformation locking potential of intramolecular S O halogen bond.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19515号 / 理博第4175号 / 新制||理||1599(附属図書館) / 32551 / 京都大学大学院理学研究科化学専攻 / (主査)教授 丸岡 啓二, 教授 大須賀 篤弘, 教授 依光 英樹 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Nos últimos anos, o desenvolvimento e a aplicação de sondas contendo átomos de calcogênio, expandiu significativamente, devido principalmente à reatividade dos elementos dessa família que são facilmente oxidados aos seus correspondentes calcogenóxidos e calcogenonas, permitindo diversas aplicações, especialmente em sistemas biológicos. A inserção de átomos pesados como os calcogênios, ao núcleo fluorofórico, leva à supressão de fluorescência, processo conhecido por \"efeito do átomo pesado\" também atribuída por Transferência Eletrônica Fotoinduzida (Photoinduced Electron Transfer). A oxidação do calcogênio ao correspondente calcogenóxido ou calcogenona inibe esse processo reestabelecendo a fluorescência. Todavia, moléculas com núcleo fluorofórico contendo, principalmente, os átomos de selênio e telúrio tem suas propriedades fotofísicas pouco investigadas, se comparado com moléculas contendo o átomo de enxofre. Neste trabalho foi tratado do desenvolvimento de metodologias de preparação de sondas contendo os átomos de selênio (II) e telúrio (II), mais especificamente, através da funcionalização da 7-hidróxi-4-metil-cumarina. Foram preparadas 6 calcogeno-cumarinas inéditas em rendimentos que variaram de 27% a 69%. Esses compostos apresentaram comportamento fluorescente condizente com o que havia sido idealizado: suas propriedades fotofísicas foram determinadas em acetonitrila, a 298 K, observando-se máximos de absorção em 290 nm e em 320 nm e máximo de emissão de fluorescência em 380 nm. Demais propriedades fotofísicas como rendimento quântico e tempo de vida do estado excitado também foram obtidas. Também foram realizados estudos com os compostos sintetizados frente a espécies oxidantes endógenas (ClO- e H2O2) permitindo inicializar estudos em sistemas celulares, observando-se que as cumarinas contendo o átomo de telúrio (II) demonstraram resultados promissores para seu uso como sondas fluorescentes. / In the last years, the development and application of chalcogen-containing dyes has expanded significantly, mainly due to the chalcogen elements reactivity that are are easily oxidized to their correspondent chalcogenides and chalcogenones, allowing several applications, especially in biological systems. The insertion of heavy atoms such as chalcogens to the fluorophoric core of the molecule leads to a fluorescence suppression, process known as \"heavy atom effect\", also attributed as Photoinduced Electron Transfer (PeT). The chalcogen oxidation to its correspondent chalcogenoxide or chalcogenone inhibts this process reestablishing the fluorescence of the molecule. However, fluorophoric molecules containing selenium and tellurium are not very investigated towards its photophysical properties if compared to their sulfur analogues. It is discussed in this this work, the development of methodologies for the preparation of probes containing selenium (II) and tellurium (II), more specifically, through the functionalization of the 7-methyl-4-hydroxi-coumarin. Six novel chalcogen-coumarins were prepared presenting yields varying from 27% to 69%. These compounds presented consistent fluorescent behavior for what it was predicted: their photophysical properties were determined observing absorption maxima at 290 nm and 320 nm and fluorescence maxima at 380 nm. Other photophysical properties such as quantum yields and excited state lifetime were also obtained. Studies with the synthetized compounds related to their behavior against endogenous oxidant species (ClO- and H2O2) were also conducted, allowing initial studies in cell systems, which demonstrated that the tellurium (II) derived coumarins presented promising results as fluorescent probes

Nos últimos anos, o desenvolvimento e a aplicação de sondas contendo átomos de calcogênio, expandiu significativamente, devido principalmente à reatividade dos elementos dessa família que são facilmente oxidados aos seus correspondentes calcogenóxidos e calcogenonas, permitindo diversas aplicações, especialmente em sistemas biológicos. A inserção de átomos pesados como os calcogênios, ao núcleo fluorofórico, leva à supressão de fluorescência, processo conhecido por \"efeito do átomo pesado\" também atribuída por Transferência Eletrônica Fotoinduzida (Photoinduced Electron Transfer). A oxidação do calcogênio ao correspondente calcogenóxido ou calcogenona inibe esse processo reestabelecendo a fluorescência. Todavia, moléculas com núcleo fluorofórico contendo, principalmente, os átomos de selênio e telúrio tem suas propriedades fotofísicas pouco investigadas, se comparado com moléculas contendo o átomo de enxofre. Neste trabalho foi tratado do desenvolvimento de metodologias de preparação de sondas contendo os átomos de selênio (II) e telúrio (II), mais especificamente, através da funcionalização da 7-hidróxi-4-metil-cumarina. Foram preparadas 6 calcogeno-cumarinas inéditas em rendimentos que variaram de 27% a 69%. Esses compostos apresentaram comportamento fluorescente condizente com o que havia sido idealizado: suas propriedades fotofísicas foram determinadas em acetonitrila, a 298 K, observando-se máximos de absorção em 290 nm e em 320 nm e máximo de emissão de fluorescência em 380 nm. Demais propriedades fotofísicas como rendimento quântico e tempo de vida do estado excitado também foram obtidas. Também foram realizados estudos com os compostos sintetizados frente a espécies oxidantes endógenas (ClO- e H2O2) permitindo inicializar estudos em sistemas celulares, observando-se que as cumarinas contendo o átomo de telúrio (II) demonstraram resultados promissores para seu uso como sondas fluorescentes. / In the last years, the development and application of chalcogen-containing dyes has expanded significantly, mainly due to the chalcogen elements reactivity that are are easily oxidized to their correspondent chalcogenides and chalcogenones, allowing several applications, especially in biological systems. The insertion of heavy atoms such as chalcogens to the fluorophoric core of the molecule leads to a fluorescence suppression, process known as \"heavy atom effect\", also attributed as Photoinduced Electron Transfer (PeT). The chalcogen oxidation to its correspondent chalcogenoxide or chalcogenone inhibts this process reestablishing the fluorescence of the molecule. However, fluorophoric molecules containing selenium and tellurium are not very investigated towards its photophysical properties if compared to their sulfur analogues. It is discussed in this this work, the development of methodologies for the preparation of probes containing selenium (II) and tellurium (II), more specifically, through the functionalization of the 7-methyl-4-hydroxi-coumarin. Six novel chalcogen-coumarins were prepared presenting yields varying from 27% to 69%. These compounds presented consistent fluorescent behavior for what it was predicted: their photophysical properties were determined observing absorption maxima at 290 nm and 320 nm and fluorescence maxima at 380 nm. Other photophysical properties such as quantum yields and excited state lifetime were also obtained. Studies with the synthetized compounds related to their behavior against endogenous oxidant species (ClO- and H2O2) were also conducted, allowing initial studies in cell systems, which demonstrated that the tellurium (II) derived coumarins presented promising results as fluorescent probes

The research on phosphorus-chalcogen compounds enjoys a long tradition in the field of inorganic chemistry, which has led to applications such as strike-anywhere matches, precursors for metal chalcogenide thin films and versatile reagents in organic synthesis. Whereas a wide range of phosphorus-sulfur and -selenium systems is known, the literature lacks information about compounds incorporating phosphorus-tellurium bonds. This thesis describes fundamental studies that develop the basic understanding of the synthesis of phosphorus-tellurium systems and the structural characteristics of these species. The focus will be on cyclic structural motifs as these offer novel bonding modes and often an interesting reactivity. In addition, the novel compounds are compared with the properties of the sulfur and selenium analogues. Three different approaches were developed to stabilise and study compounds incorporating phosphorus-tellurium bonds: a) Stabilisation of binary organophosphorus-tellurium heterocycles by bulky substituents, b) the utilisation of P₂N₂ rings based on the dianions [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) and c) the peri-substitution of phosphorus and tellurium atoms on an acenaphthene backbone. The use of sterically demanding substituents led to the isolation of the first series of structurally characterised organophosphorus(III)-tellurium heterocycles of the type (RP)[sub]nTe[sub]m including three- to six-membered ring systems. The mild oxidation of [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) with iodine yielded macrocyclic (S, Se) or oligomeric systems (Te). Furthermore, a collection of novel P₂N₂-supported phosphorus-chalcogen heterocycles incorporating main group elements was synthesised employing [{EP(NtBu)(μ-NtBu)}₂]²⁻ (E = S, Se, Te) in metathetical reactions with main group element halides. Extension of this approach to transition metal halides generated some unusual metallocycles, as well as macrocycles and ladders incorporating coinage metals. The first peri-substituted phosphorus-tellurium species were studied regarding their interatomic and intermolecular forces. Systems of the general formula RTe–Acenap–P(iPr)₂ were shown to exhibit extensive through-space spin-spin coupling. In addition, the influence of oxidation and complexation on these interactions was investigated and the formation of peri-substituted phosphorus-tellurium cations exhibiting P–Te bonds was observed.

The family of polycyclic aromatic hydrocarbons naphthalene, acenaphthene and acenaphthylene, containing rigid organic backbones, allow the study of non-bonded intramolecular interactions. Due to the rigid framework, heteroatoms that are substituted at the peri-positions (positions 1- and 8- of the naphthalene ring and positions 5- and 6- of the acenaphthene and acenaphthylene rings) are forced to occupy space that is closer than the sum of their van der Waals radii, resulting in severe steric strain and unique interactions. In spite of this, a vast amount of peri-substituted naphthalenes have been prepared, however acenaphthene and acenaphthylene compounds have received much less attention. Preparation of these sterically crowded systems is possible because of the backbones ability to relieve strain as a result of both attractive and repulsive interactions. Attractive interactions relax the backbone via formation of weak or strong bonds between the substituents. Alternatively, repulsive interactions can result in the deformation of the backbone away from its natural geometry by buckling the ring system and causing the peri-bonds to distort in-plane and out-of-plane. Peri-substituted systems can also ease strain by forming compounds with bridging atoms or through bidentate coordination to form metal complexes with, for example, metal bis(phosphine) or bis(thiolate) moieties. The competition between attractive and repulsive forces, the method by which peri-substituted compounds relieve steric strain, is investigated in this thesis using a variety of different peri-moieties and the aforementioned organic backbones. Chapter 2 initially focuses on the formation of a series of platinum bis(phosphine) complexes, constructed from corresponding peri-substituted naphthalenes, 1,8-naphthosultone and 1,8-naphthosultam, the chemistry of which is outlined in Chapter 1. A corresponding study of platinum bis(phosphine) complexes, constructed from analogous 5,6-dihydroacenaphtho[5,6-cd]-1,2-dithiole and 5,6-dihydroacenaphtho[5,6-cd]-1,2-diselenole bidentate ligands is provided in Chapter 6. The chemistry of peri-substituted naphthalenes is well documented and a number of reviews have been written on this subject. Chapter 3, meanwhile, reviews the chemistry of related acenaphthene and acenaphthylenes which have seen increasing use in the literature over the last few years. Chapter 4 investigates the relationship between repulsive and attractive interactions that occur between the peri-substituents in a series of bis-chalcogen, mixed chalcogen-chalcogen and mixed halogen-chalcogen acenaphthylenes. By comparison with their known naphthalene and acenaphthene counterparts, the effect the rigid aromatic ring system has on the molecular geometry is examined. Finally, Chapter 5 looks at a series of acenaphthene and acenaphthylene compounds containing ArTe peri-substituents and explores how repulsive and attractive interactions affect molecular conformation and Te•••Te spin-spin coupling constants.

No description available.

The major aim of research reported on this thesis uses X-ray crystallography to investigate the structural features of a series of pentafluorosulfuranyl (SF₅) containing aromatic compounds, chalcogen amides, 2,4-diaryl-1,3-selenazoles and 2,4-diaryl-1,3-chalcogen azoles bearing SF₅ group and organo phosphorus-chalcogen macrocycles incorporationg double OP(S)SC[sub]n or OP(Se)SeC[sub]n scaffolds. The basic theory of crystallography is introduced in Chapter 1, followed by a general discussion on pentafluorosulfuranyl (SF₅) containing heteroatom compounds and sulfur/selenium heterocycles in Chapter 2. Ten pentafluorosulfuranyl (SF₅)-containing aromatic compounds have been studied crystallographically in Chapter 3. All S-F bond lengths in these compounds are very similar [1.571(3) to 1.618(3) Å and 178.5(3) to 180.0° for the C-S-F(ax) bond] and the angles of two adjacent F(eq) is approximate to 90°. The intramolecular C[sub](aryl)-H···F(eq) and intermolecular C[sub](aryl)-H···O/N/F/Cl interactions, and π-stacking interactions are observed in the packing frameworks. X-ray crystal structure analysis reveals that in the structures of 2,4-diaryl-1,3-selenazoles in Chapter 4, the five-membered N-C-Se-C-C rings have either planar or near-planar conformations, and exhibit a series of the intramolecular and intermolecular C-H∙∙∙O/N/Se/Br/Cl) interactions and π-stacking interactions. The crystal structures of 2,4-diaryl-1,3-chalcogen azoles with both a pentafluorosulfuranyl (SF₅) group and a five-membered N-C-Se-C-C ring have been investigated in Chapter 5. A diverse picture of molecular configuration and intramolecular/intermolecular C-H∙∙∙N/Se/S and π-stacking interactions information are disclosed in selenamide, thiamides, 1,3-selenazoles and 1,3-thiazoles. Nine organo phosphorus-chalcogen macrocycles with nine- to fifteen-membered ring incorporating double OP(S)SC[sub]n or OP(Se)SeC[sub]n scaffolds have been discussed crystallographically in Chapter 6. The similar intramolecular and intermolecular C-H∙∙∙O, C-H∙∙∙S or C-H∙∙∙Se interactions are observed to lead to the similar packing networks.