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Studies on the Synthesis and Structural Characterizations of the New Transition Metal Chalcogenides
- Author(s)
- 윤우진
- Alternative Author(s)
- Yoon Woojin
- Advisor
- 윤호섭
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2022-08
- Language
- eng
- Alternative Abstract
- PART 1. Two-Step Hybrid Synthesis The new quaternary alkali-metal chromium thiophosphates, ACr3P2S10, ACrPS5, and A2CrPS6 (A = Rb, Cs) have been synthesized by solid-state reaction of pure elemental powders with reactive halide fluxes at high temperature (First step). The crystal structures have been determined by single crystal X-ray diffraction techniques. The title compounds have octahedral CrS6 and tetrahedral PS4 as basic building units. These units are linked by edge sharing S atoms to form anionic species, _∞^( 2)[Cr3P2S10-] layers, _∞^( 1)[CrPS5-] chains, and _∞^( 0)[CrPS62-] isolated clusters. Of these, ACrPS5 and A2CrPS6 consist of Cr2P2S12x-, the anionic binuclear cluster formed by two pairs of units sharing edges. These anionic chromium thiophosphates and alkali metal cations, A+ are bound through ionic interactions stabilizing the overall structure. The charge valences derived from the structure of ACr3P2S10, ACrPS5, and A2CrPS6 can be described as [A+][Cr3+]3[P5+]2[S2-]10, [A+][Cr4+][P5+][S2-]5, and [A+]2[Cr5+][P5+][S2-]6, respectively. To the best of our knowledge, ACrPS5 and A2CrPS6 are the first examples of the tetravalent and pentavalent Cr ion in thiophosphates. In the second step, these alkali-metal chromium thiophosphates prepared through solid-state reactions were dissolved in polar solvents such as water, NMF, and DMF and new ionic species were found through ion exchanges. The precursor, Cs2CrPS6 was dissolved in water and PPh4Cl was added to replace the Cs+ ion. As a result, a new compound, Cr2P2S8(H2O)4·2PPh4Cl·10H2O was isolated as single crystals. The crystal structure of this compound has been determined by single crystal X-ray diffraction techniques. In the precursor Cs2CrPS6, the terminal S atoms of CrS6 octahedra was replaced by the oxygen atoms of the water molecule to form a new neutral binuclear cluster, Cr2P2S8(H2O)4. These clusters are infinitely connected through hydrogen bonds with crystal waters and Cl- ions in the direction parallel to the ac-plane to form the layers. Between these layers, PPh4+ cations are located, completing the three-dimensional structure. The charge valences of this compound can be described as [PPh4+]2[Cr3+]2[P5+]2[S2-]8[Cl-]2[H2O]14 and oxidation state of the Cr ion in the precursor is reduced from +5 to +3. PART 2. New Hexanary Phases The new hexanary two-dimensional niobium(V) thiochlorophosphates, ANbPO4SCl (A = K, Rb, Cs) have been synthesized through reactive alkali metal halide flux methods and structurally characterized by single crystal X-ray diffraction techniques. They are isostructural and they crystallize in the space group P4/nmm of the tetragonal system. Each niobium atom is surrounded by one chlorine, one sulfur, and four oxygen atoms in the distorted octahedral fashion and phosphorus atom is coordinated by four oxygen in a tetrahedral geometry. These polyhedra are combined to form the two-dimensional infinite anionic layers, _∞^( 2)[NbPO4SCl-]. Alkali metal ions reside between the layers to stabilize the three-dimensional structures. To the best of our knowledge, the octahedral coordination around Nb in this phase NbO4SCl is the first example that has not yet been reported. In addition, pentanary, ANbPO5Cl and non-stoichiometric hexanary, ANbPO4SexO(1-x)Cl (A = Rb, Cs) were synthesized through additional experiments and their structure were analyzed. The classically charged valences of these phases can be described as [A+][Nb5+][P5+][O2-]4[S2-][Cl-], [A+][Nb5+][P5+][O2-]5[Cl-], and [A+][Nb5+][P5+][O2-]4[Se2-]x[O2-](1-x)[Cl-]. In this work, we discuss the nature of bonds around the Nb atoms based on bond valence analysis.
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- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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