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2 1999

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Elektrochemiczne właściwości stałych warstw z udziałem fulerenów

Winkler Krzysztof, Płońska Marta E.

Wiadomości Chemiczne

1999

[Z] 53, 11-12

823--870

This paper reviews the results of the investigation of electrochemical properties of fullerenes and their derivatives in solid state. These systems can be divided into three groups: (i) crystalline thin films, (ii) non-crystalline Langmuir-Blodgett (LB) films and self-assembled monolayers (SAM), (iii) fullerene-based polymers. The electrochemical behaviour of crystalline films of fullerenes is very different from that of dissolved species. The method of the film preparation strongly influences the redox properties and morphology of the film. Fullerene films are composed of small crystallites. The layers grown upon vapour deposition and electrocrystallisation are more uniform than the solution (solvent)-cast films. The redox behaviour of crystalline fullerene films in polar solvents is mainly affected by the size of supporting electrolyte cations. For small cations of alkali and alkaline-earth metals a rapid deterioration in the electrochemical properties of fullerene films is observed during repeated potential cycling. This behaviour of the layer is attributed to the formation of an electrochemically inactive cation intercalated compound or dissolution of the fullerene salt. The manipulation of the time window of experiment and the solvent nature can favour one of the above processes over the other.(...) The voltammetric behaviour of LB films and SAMs containing fullerenes and their derivatives are less influenced by the medium. A much smaller structural reorganization upon electrochemical reactions is observed. Redox properties of the fullerene moieties in these structures are similar to these observed in solution. Tightly packed C(60) containing self-assembled layers exhibit resistive behaviour due to the resistance to ion incorporation. (... ) The polymeric network can also be formed through a copolymerization that utilises the formation of covalent bonds, between transition metal complexes and fullerenes. These films are insoluble in common organic solvents and adhere strongly to the electrode surface. They display very stable redox behaviour due to the presence of fullerene moieties in their structures. A significant decrease in resistivity in the potential region in which it is reduced is also observed. The rlrctrochemical switching between the doped (conducting) and undoped (non-conducting) states involves both electron and ion transport within the film. The overall control of charge percolation through electroactive material is governed by the transport of ions. Laser ablation of some of these electrochemically formed layers results in the formaton of C(59-2n)M (M=Pt and Ir) clusters.

Elektrochemiczne właściwości fulerenow i ich pochodnych w roztworach

Winkler Krzysztof

Wiadomości Chemiczne

1999

[Z] 53, 7-8

479-528

(...) W badaniach fizykochemii fulerenów szczególnie wiele uwagi poświęcono ich właściwościom elektrochemicznym. Fulereny są doskonałymi akceptorami elektronów. Molekuły C60 i C70 ulegają wielostopniowej, odwracalnej redukcji z wytworzeniem stabilnych sześcioujemnie naładowanych jonów w dostatecznie ujemnym zakresie potencjałów. Nie mniej interesująca jest elektrochemia pochodnych fulerenów. Ze względu na doskonałą sferyczną symetrię oraz znajomość rozkładu poziomów elektronowych, cząsteczka C60 jest idealnym układem modelowym do testowania teorii heterogennego przeniesienia ładunku. Z elektrochemią wiąże się też wiele aspektów praktycznych. Powstające w warunkach elektrochemicznej redukcji ujemnie naładowane jony fulerenowe mogą stanowic reduktory w procesach syntezy organicznej. Wiele uwagi poświęcono też badaniu elektrochemicznych własności stałych faz fulerenowych. Praktycznym aspektem tych badań było określenie możliwości wykorzystania soli anionów fulerenowych jako elektrolitów w ogniwach galwanicznych. Prezentowana praca stanowi próbę usystematyzowania wyników badań dotyczących elektrochemicznych właściwości fulerenów w roztworach.

Fifteen years after the discovery of fullerenes the volume of work in the field of fullerene chemistry continues to expand at an ever-increasing rate. The electrochemical behaviour of C60 and other fullerenes received considerable attention. Up to six reversible, one-electron reduction steps have been observed for C60 and C70, while only one, oxidation step at quite positive potential , has been detected. These results are in accordance with the theoretical predictions based on the energy levels distribution in fullerene molecules. The electron transfer processes are coupled with the ion-pair formation reactions. Heteroelectrochemical behavior of higher fullerenes has been also reported. Significant differences in oxidation and reduction potentials have been observed for isomers of higher fullerenes. Electrochemical properties of fullerene derivatives depend on a degree of inductive effect and the number of adducts bonded to the fullerene cage. The electrochemical properties of five distinct types of derivatives have been studied: metallofullerenes, inclusion complexes, transition metal complex adducts and inorganic and organic group adducts. (...) The electrochemistry of organofullerenes is very similar to C60 with a negative shift in the reversible reduction potentials mainly due to the inductive effect of the adducts. Commonly , three-, five- or six-membered rings outside the fullerene cage are formed by 1,2 addition of organic compounds. For five-member ring derivatives the electrochemically induced cyclopropane-fulleroid isomerization has been observed. Among the C60 containing dimers only C120O exhibits the electrochemical behaviour indicating the electronic communication between fullerene units. C120 dimer is unstable and after first reduction step decomposes with the formation of neutral C60 and C60- ion. This paper review the results of the investigation of electrochemical properties of fullerenes and their derivatives.