Synthesis, structure and characterization of molybdenum and rare earth chalcogenides /
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| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University],
[2004]
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| Subjects: | |
| Online Access: | Link to OAK Trust copy |
| Abstract: | This dissertation focuses on the synthetic exploratory synthesis of molybdenum chalcogenides and rare earth metal-rich ternary tellurides as a part of an effort to produce molecular building blocks of molybdenum chalcogenide clusters and to explore their structural relationships with solid state cluster networks. The tightly cross-linked Mo₃nSe₃n+2(n = 2, 3, ...[infinity symbol] clusters and chain compounds react with alkali metal cyanide or cyanide salt mixtures at temperatures of 450-675 °C to yield reduced, cyanide-terminated molybdenum chalcogenide clusters that are thermodynamically stable. At temperatures of 650-675 °C, linear chain compounds M¹₆[Mo₆Se₈(CN)₄(CN)₂/₂] (M¹= K, Cs) were prepared from reactions of Mo₆Se₈ or elemental starting materials, Mo and Se with excess molten cyanide (KCN, CsCN). These are the first known compounds to feature linking of Mo₆Se₈ clusters via cyanide bridges. Magnetic susceptibility and EPR measurements indicate that there is one unpaired electron per cluster. A new reduced molecular octahedral complex, Na₈[Mo₆Se₈(CN)₆]·20H₂O was prepared by the reduction of [Mo₆Se₈(CN)₆]⁷- with Zn in an aqueous NaCN solution. Single crystal structure was determined. Cyclic voltammetric measurements in basic aqueous media show multiple reversible redox waves corresponding to [Mo₆Se₈(CN)₆]⁶-/⁷-, [Mo₆Se₈(CN)₆]⁷-/⁸-, [Mo₆Se₈(CN)₆]⁸-/⁹- redox couples with half-wave potentials of E₁/₂ = -0.442 V, -0.876 V, and 11.369 V respectively versus the standard hydrogen electrode (SHE). UV-Vis studies support the presence of the reduced cluster compound. New reduced molecular tetrahedral complexes, K₇Na[Mo₄Se₄(CN)₁₂]·5H₂O·MeOH, Na₄Cs₇[Mo₄Se₄(CN)₁₂]Cl₃, Na₈[Mo₄Se₄(CN)₁₂], and Na₄K₄[Mo₄Se₄(CN)₁₂]·12H₂O were prepared. Preparation of Na₈[Mo₄Se₄(CN)₁₂] is an improved method for the synthesis of the Mo₄Se₄ core. Half-wave potentials of E₁/₂ for the [Mo₄Se₄(CN)₁₂]⁶-/⁷-and [Mo₄Se₄(CN)₁₂]⁷-/⁸-couples are 0.233 V, and -0.422 V respectively versus SHE. The molecular cubane clusters [Mo₄Se₄(CN)₁₂]⁷-/⁸-play an essential role in the process by which the discrete [Mo₆Se8(CN)₆]⁶-and [Mo₆Se₈(CN)₆]⁷- are excised from the CN-linked chain compound, K₆Mo₆Se₈(CN)₅. A new rare-earth telluride compound with the empirical composition of Gd₄NiTe₂ was synthesized from a high-temperature solid-state reaction. Gd₄MTe₂ (M = Ni) crystallizes in the orthorhombic space group Pnma. This unprecedented structure consists of a cluster condensation of Ni-centered gadolinium tricapped trigonal prisms along the rectangular faces of the trigonal prism such that the Ni atoms act as two of the caps to the trigonal prisms. |
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| Item Description: | "Major Subject: Chemistry" Title from author supplied metadata (record created on Nov. 30, 2005.) Vita. Abstract. Electronic resource. |
| Physical Description: | 1 online resource. |
| Format: | System requirements: Adobe Acrobat Reader. |
| Bibliography: | Includes bibliographical references. |