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abstract: New sol-gel routes based on peroxo complexes of early transition metals in a highly acidic medium were developed, to prepare metal oxide phosphates that feature structural protons. A sol-gel synthetic route was chosen because it allows atomic level mixing of precursors and lower heating temperatures, which are preferable in exploring metastable phases. Titanium and molybdenum sol-gel chemistries were the focus of the initial studies and the synthesis of Ti1-xMoxP2O7 (x = 0 – 0.5) and Mo1-yTiyP2O8-y (y = 0 – 0.4) type metal oxide phosphates were explored. For the synthesis of the metal oxide phosphates, hydrogen peroxide was employed to prepare the respective precursor solutions. The peroxide ligand suppressed the immediate precipitation of metal cations in aqueous medium, by coordinating to Ti4+ and Mo6+ ions, and produced a soft wet-gel following polycondensation. Phosphoric acid was used to acidify the reaction medium and to provide protons and phosphate ions as structural components. From this synthetic route, a series of Ti1-xMoxP2O7 (x = 0 – 0.5) and Mo1-yTiyP2O8-y (y = 0 – 0.4) crystalline compounds, with various degrees of purity, were synthesized. For x = 0 and y = 0, the crystalline compounds TiP2O7 and MoP2O8 were produced, respectively, after calcining at 600 °C. In pursuit of new metastable molybdenum oxide phosphate compounds, peroxo-molybdenum precursor mixtures with different molar ratios were treated gently by low-temperature heating. After controlled drying in a lab oven, MoO2(H2O)(HPO4) crystals were obtained as a highly crystalline pure product instead of a gel. The dissolution of MoO2(H2O)(HPO4) in water and precipitation with a CsCl solution produced a new crystalline compound with a cubic unit cell (a = 11.8(2) Å). Further studies will lead to crystal structure determination and elucidation of the aqueous chemistry of MoO2(H2O)(HPO4). / Dissertation/Thesis / Masters Thesis Chemistry 2018

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Solar energy is the most abundant efficient and important source of renewable energy. The objective of this study is to develop highly efficient visible light responsive photocatalysts for overall water splitting. This is done by using silver or copper containing materials. Phosphate compounds have caught much attention due to their rigid structure, thermal stability and resistance to chemical attacks. Solid phosphates can be prepared by direct solid-state reaction between metal cations and phosphate anions at high temperatures. Double metal phosphates of the Nasion-type structure had shown further technological importance. It has been reported that well-crystallized double metal phosphate particles have excellent ordering and cationic conduction channels in the Nasicon framework. In this study, several Nasion-type structured materials have been synthesized by solid-state method (e.g. CuTi2(PO4)3 and AgTi2(PO4)3) heated up under different temperatures (400–1100C) in N2 or air atmosphere. These materials were characterized by XRD, SEM, DR-UV-Vis spectroscopy and tested for photocatalytic applications. A new method for direct synthesis of photoelectrode on Ti Plate had been demonstrated. Further investigations on controlling the size and morphology for better performance of single and double metal phosphates will be done.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第17887号 / 工博第3796号 / 新制||工||1581(附属図書館) / 30707 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19519号 / 理博第4179号 / 新制||理||1600(附属図書館) / 32555 / 京都大学大学院理学研究科化学専攻 / (主査)准教授 中西 和樹, 教授 北川 宏, 教授 有賀 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

New iron phosphate and borophosphate compounds were synthesized and characterized by single crystal/powder X-ray diffraction, infrared spectroscopy, raman spectroscopy, thermogravimetric analysis, electron microscopy and elemental analysis. Using several compositions, Fey B(PO4)x type of compounds were attempted to be prepared by solid state reactions. The solid state reactions of boron compounds with a phosphating agent has been completed at 950oC. A new product Fe2BP3O12 is synthesized and indexed in this work which is isostructural with Cr2 BP3O12 A single crystal of iron ammonium phosphate, (NH4)3-xHxFeP3O12, was synthesized by a hydrothermal method and characterized. Its X-ray powder diffraction pattern was indexed in orthorhombic system. The unit cell parameters were found to be as a = 7.775 (&Aring / ), b = 7.445(&Aring / ), c = 14.331(&Aring / ) The compound with the formula NH4FeBP2O8OH was synthesized by hydrothermal method. Its X-ray powder diffraction pattern was indexed in monoclinic system. The unit cell parameters were found to be a = 9.336, b = 8.278, c =9.642&Aring / , and &amp / #946 / = 101.60o, which are good agreement with the literature values. Ferro-axinite type of compound was discovered as single crystals resembling the axinite mineral. The compound was indexed in triclinic system with the unit cell parameters of a = 7.167, b = 8.840 , c = 9.455&Aring / , &amp / #945 / = 64.83o, &amp / #946 / = 64.83o, &amp / #947 / = 69.42o. A zeotype Fe(H2O)2BP2O8.H2O, which was obtained by hydrothermal methods before, was synthesized by a precipitation method using different initial reactant. In this case, instead of Fe+2, Fe+3 compound was used as a reactant. All the compounds have been investigated by FTIR spectroscopy and the assignments of the functional BO3, BO4 and PO4 groups have been done.

Open-framework inorganic and inorganic-organic hybrid materials constitute an important area of study in materials chemistry, because of their potential applications in areas such as sorption and catalysis. Besides aluminosilicate zeolites, the metal phosphates and carboxylates constitute large families of open-framework structures. The possibility of building open architectures with the sulfate and selenate anions as the basic building units has been explored in this thesis. Investigations of a variety of open-framework metal sulfates and selenates, as well as a family of jarosites of different transition metals are presented. More importantly, studies directed towards the synthesis and understanding of the magnetic properties of various Kagome compounds formed by the transition metal ions is discussed at length. After providing an introduction to inorganic open-framework compounds (Part 1), the thesis presents the results of the investigations of various transition and rare earth metal sulfates with diverse structures and dimensionalities in Part 2. Some of these compounds show interesting properties. For example, a two-dimensional Ni(II) sulfate exhibits ferrimagnetism whereas a three-dimensional Ni(II) sulfate with 10-membered channels is paramagnetic. A family of three-dimensional co-ordination polymers of Co(II) sulfate wherein the Co(II) sulfate layers are linked by diaminoalkanes of varying chain length has been synthesized and characterized. Organically-templated neodymium and thorium sulfates with layered and three-dimensional structure have also been prepared. The jarosite family of compounds with the Kagome structure is considered as an ideal model for studying frustrated magnetism. This type of materials, however, is difficult to prepare in a pure and highly crystalline form. We have synthesized analogues of the jarosite containing magnetic ions other than Fe3+ by solvothermal techniques and discussed them in Part 3. In particular, we have prepared and explored the magnetic properties of Mn2+(S = 5/2), Fe2+ (S = 2), Co2+(S = 3/2) and Ni2+ (S = 1) jarosites. Based on the results presented, it becomes clear that the magnetic properties vary with the spin of the transition metal ion. It appears that those Kagome compounds with transition metalions with non-integer spins show antiferromagnetic interactions and magnetic frustration while those with integer spins exhibit ferro/ferrimagnetic properties. A theoretical study has also supports this observation. We have been able to isolate for the first time 1,4-diazacubane as the part of the structure of the nickel Kagome compound. The possibility of building open architectures with the selenate anion as the basic building unit has been explored in Part 4. The results have been rewarding and an organically-templated three-dimensional lanthanum selenate with 12-membered channels has thus been obtained for the first time.

Open-framework materials constitute an important area of study in materials chemistry, because of their potential applications in areas such as sorption and catalysis. Furthermore, these materials exhibit fascinating architectures with unusual bonding and coordination patterns. Besides aluminosilicate zeolites and metal phosphates, metal carboxylates constitute an important family of open-framework structures. In this thesis, results of investigations of a variety of open-framework metal carboxylates, as well as a new family of rare-earth sulfates are presented. More importantly, studies directed towards an understanding of the mechanism of formation of open-framework phosphates and carboxylates and the importance of synthesis parameters like temperature in determining the dimensionality of the products are discussed at length. After providing an introduction to open-framework compounds (Part 1), the thesis (Part 2) presents the results of the investigations of metal carboxylates employing both transition metal and rare-earth metal ions with various organic linkers, ranging from aromatic squarate dianion, aliphatic dicarboxylates like oxalate, adipate, succinate, aminocarboxylates (which contain both the amine and the carboxylate group in the same moiety) and dihydroxybenzoates. Some of these compounds have large channels, for example, both the lanthanum mixed aliphatic dicarboxylates, strontium dihydroxybenzoate etc. Some even show unusual properties, example, a mixed valent iron (II, III) glycinate has a perfect kagome structure and shows unusual magnetic properties, entirely different from those of ordinary Fe(III) kagome structures, copper derivative of 6-amincaproic acid has large channels and remains crystalline porous even after dehydration, a cobalt oxalato-squarate has both oxalate and squarate moiety in the same structure, where the oxalate is produced in situ by the oxidation of squarate under hydrothermal conditions in the basic medium. While the phosphate and the silicate anions are the most common basic building units in open-framework inorganic structures, the possibility of building open architectures with the sulfate anion as the basic building unit has been explored in Part 3. The results have been rewarding and both layered and three-dimensional rare-earth sulfates with large channels and possessing a α-Po structure or (6, 3) nets with continuous M-O-M connectivity in two dimensions have been obtained. The most intriguing question in the area of open-framework structures relates to the mode of formation. In Part 4, the mechanism of formation of both metal phosphates and metal carboxylates have been discussed. This part includes a study of the transformations of four-membered ring phosphates to higher dimensional structures (like 3D sodalite-related structure), through lower-dimensional structures, involving a progressive building-up mechanism. Similar progressive building-up mechanism has also been studied for metal carboxylates. The importance of synthesis parameters like temperature in governing the dimensionality of the products has been studied.

Ce travail consiste en l’étude par RMN multinoyaux de matériaux paramagnétiques d’électrodes positives pour batteries au Li. La RMN du solide permet une caractérisation de l’environnement local du noyau sondé grâce à l’exploitation des interactions hyperfines dues à la présence d’une certaine densité d’électrons célibataires (déplacement de contact de Fermi) ou de conduction (déplacement de Knight) sur ce noyau (densité transférée selon des mécanismes plus ou moins complexes). Les matériaux étudiés sont des phosphates de métaux de transition tels que Li3M2(PO4)3 (M = Fe, V), la famille des tavorites LiMPO4X (M = Fe, Mn; X = OH, F) ou encore les phases homéotypiques MPO4.H2O (M = Fe, Mn, V). Pour tous ces matériaux, caractérisés par RMN du 7Li, 31P et 1H, l’environnement local de ces noyaux a été étudié afin d’envisager les mécanismes de transfert de spin possibles. Des calculs ab initio ont été effectués pour reproduir les déplacements de RMN, puis établir des cartes de densité de spin afin d’étayer ou compléter la compréhension de ces mécanismes. / Paramagnetic materials for positive electrodes for Li batteries have been studied by multinuclear NMR. The local environment of the probed nucleus can be characterized by solid state NMR making use of hyperfine interactions due to transfer of some electron spin density (Fermi contact shift) on this nucleus, via more or less complex mechanisms. We studied a series of transition metal phosphates as Li3M2(PO4)3 (M = Fe, V) with anti-NASICON structure, LiMPO4X (M = Fe, Mn; X = OH, F) belonging to the tavorite family and the homeotypic phases MPO4.H2O (M = Fe, Mn, V). All these materials have been characterized by 7Li, 31P and 1H NMR, and the local environments of these nuclei have been analyzed to propose possible spin transfer mechanisms. First principles DFT calculations have been carried out to, first of all, reproduce the experimental NMR shifts, and then to confirm or complement the understanding of these mechanisms, in particular by plotting spin density maps.