Browsing by Author "Kandaiah, Sakthivel"

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Electrochemical synthesis of new coordination compounds with divalent silver, metallo-phthalocyanines and organic charge transfer crystals
(2010) Kandaiah, Sakthivel; Jansen, Martin (Prof. Dr. Dr. h. c.)
The synthesis of new compounds, their crystal structures, as well as the electronic and magnetic properties of solids are of principal interest in the field of solid state chemistry. There are several methods adapted for the preparation of new crystalline, amorphous, polymeric and glassy materials. The electrochemical method of synthesis of solids enjoys some advantages over other methods, though it also has some limitations. An important characteristic of electrocrystallization techniques is that they usually produce large, good-quality single crystals. In addition, the reaction selectivity, product formation, kinetics of reaction, crystal growth, phase purity and reproducibility are major advantages. Within the scope of this thesis the advantages of the electrochemical route for synthesis of selected crystalline solids is demonstrated. In first section, compounds featuring higher-valent silver are potentially strong oxidants, but they remain of interest since mixed-valent silver compounds were predicted to become superconducting in an analogous manner to the copper systems. The oxidation state +2 is readily accessible and stabilized by several ligands. The general method for the preparation of this oxidation state is the oxidation of silver salts in solution in the presence of an excess of ligands, which mostly results in microcrystalline precipitates. Thus preparation of larger crystals suitable for further studies is often hampered by these hard oxidation processes. The higher oxidation state of silver as stabilized within the coordination complexes was achieved by electrochemical synthesis. This also allowed various coordination geometries of the silver complexes to be prepared. The most significant experimental parameters in electrochemical synthesis are the current and the potential, as they have a major influence on the product formation. However, the influence of solvent on the phase formation was also demonstrated in the electrochemical synthesis of some compounds. Metallo-phthalocyanine compounds exhibit a high potential for various applications. Thus a steep growth in the discovery of new phthalocyanine-based compounds has already been observed. In the current work, the electrochemical method is employed for the synthesis of co-crystals of lithium phthalocyanine. In addition, the electrocrystallization of monovalent sodium phthalocyanine and synthesis of other phthalocyanine compounds is also demonstrated. Electrochemical organic synthesis has substantial advantages over traditional organic synthesis, since the latter typically involves numerous intermediate steps. In the current work, we show the electrochemical synthesis of some new organic charge-transfer crystals with different organic cations and-tetracyanoquinodimethane-anion. Finally, we discuss the electrocrystallization of the compound Ag7O8.HF2 utilizing aqueous media, and without the need for dangerous HF.