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Electrochemically Investigated pH-dependent Redox Properties of Copper Complexes of Azamacrocyclic Ligands
Koláčná, Lucie ; Maďar, M. ; Kubíček, V. ; Ludvík, Jiří
Investigated Cu(II) complexes are based on plain or cross-bridged cyclam. The\nelectrochemically inactive cyclam was modified by carboxylate, phosphonate, or phenolate\npendant arms. Cu(II) represents the main redox center of the complexes. Modification of the\nligand causes a changed pattern of complex redox response in buffered aqueous solution.\nIrreversible Cu(II) reduction results in complex decomposition to amalgamated copper and\nligand in excess. After Cu(0) electrochemical in situ re-oxidation, copper and ligand are recomplexed.\nComplexes undergo isomerization, accelerated by increasing the temperature. The\ninfluence of pH on complex isomerization and the reversibility of its reduction was described.
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Redox Properties of Conjugated Phosphole Derivatives – Electrochemical Study
Koláčná, Lucie ; Polák, P. ; Tobrman, T. ; Ludvík, Jiří
The study describes pentasubstituted phospholes with a π-conjugated arms in positions 2 and 5 of the phosphole ring. According to the expectations, substituents with electron-donating groups led to lower oxidation potentials, the presence of electron-withdrawing groups shifts the reduction potential to less negative values. Because all studied phospholes have multiple substituents of both types, their resulting potentials represent the sum of their influences. Moreover, since many of the studied compounds have two redox centers (phosphole moiety itself and the pi-conjugated arm), their locations were determined and intramolecular interactions were followed, because substituents which can be conjugated with the π-system of phosphole are able to extend the delocalized π-system resulting in stabilization of primary redox intermediates. Chemical modification of phospholes using various combinations of substituents can set the desired electrochemical properties of studied molecules.
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Differences in Electrochemical Reduction of Mono- and Polynuclear Acylgermanes
Liška, Alan ; Frühwirt, P. ; Haas, M. ; Ludvík, Jiří ; Gescheidt-Demmer, G.
Ail the studied compounds accept first electron under formation a stable anion radical. The\ncorresponding reduction potentials in aprotic media depend on electronic (inductive,\nmesomeric) properties of the substituents, their number, and position. Here, aromatic acyl group\n(benzoyl group with various substitution on aromatic ring) is the principal substituent. The\nredox properties of presented organoelement compounds with central heteroatom Ge (Si, Sn)\nare controlled by peripheral carbonyl groups (in role of redox centers), their number, and\naromatic ring substitution. The measured first reduction potentials E1 values are found in wide\nrange (> 900 mV) due to the fact that the redox centers are carbony 1 groups connected through\nheteroatom in case of acylgermanes, while for di- and trinuclear derivatives (which are\nmolecules with multiple redox centers) the easiest reducible center is the bridging aromatic unit\ninfluenced by the closest carbonyl groups. Thus, it is possible to distinguish both groups ofnonequivalent\ncarbonyl substituents.
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