Three compounds have been synthesized with formulae [3-MeRad][Ni(dmit)2] (1), [4-MeRad][Ni(dmit)2] (2) and [4-PrRad][Ni(dmit)2] (3) where [Ni(dmit)2]- is an anionic pi-radical (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) and [3-MeRad]+ is 3-N-methylpyridinium alpha-nitronyl nitroxide, [4-MeRad]+ is 4-N-methylpyridinium alpha-nitronyl nitroxide and [4-PrRad]+ is 4-N-propylpyridinium alpha-nitronyl nitroxide. The temperature-dependent magnetic susceptibility of 1 revealed that an antiferromagnetic interaction operates between the 3-MeRad+ radical cations with exchange coupling constants of J1 = - 1.72 cm-1 and antiferromagnetism assigned to the spin ladder chains of the Ni(dmit)2 radical anions. Compound 1 exhibits semiconducting behavior and 3 presents capacitor behavior in the temperature range studied (4 - 300 K).

Estudamos o fenômeno de histerese inerente aos processos redox dos polímeros condutores eletrônicos (PCE). As histereses foram separadas em duas classes: i) as histereses dinâmicas constituídas por componentes cinéticas e ôhmicas e ii) as histereses estacionárias ou termodinâmicas. Efetuamos uma análise matemática das histereses dinâmicas observadas nos voltamogramas cíclicos de dois polímeros: a polianilina (PANI) e o poli(3-metiltiofeno) (P3MT). Mostrou-se que no caso do P3MT a histerese é principalmente cinética devido à velocidade de uma das etapas do processo redox com também uma componente ôhmica relacionada à existência de uma impedância elétrica em serie com o sistema eletroquímico. No caso da PANI, observou-se que a histerese é independe da corrente, o que é característico de uma histerese termodinâmica.

The hysteresis phenomenon inherent to redox processes of Electronic Conducting Polymers (ECP) has been studied. Hysteresis was divided into two classes: i) dynamic hysteresis, containing a kinetic and an ohmic component and ii) stationary or thermodynamic hysteresis. A mathematical analysis was performed on the dynamic hysteresis observed in cyclic voltammograms of two polymers: polyaniline (PANI) and poly(3-methylthiophene) (P3MT). It has been shown that in the case of P3MT, the hysteresis is mainly kinetic due to the rate of one of the steps of the redox process. However, an ohmic component related to the existence of an electrical impedance in series with the electrochemical system is also present. As for PANI, hysteresis is current independent, which is characteristic of thermodynamic hysteresis.

Theoretical and practical aspects concerning construction and use of a thin layer electrochemical cell are presented. Construction was realized by a simple technic and geometry was optimized in order to minimize the problems of electrical resistance. A well known redox system was studied ((Fe(III)(CN)6(3-)/Fe(II)(CN) 6(4-)) using two experimental methods, cyclic voltammetry and pulse chronopotentiometry. A numerical integration based-program was developed to calculate the voltammetric current in case of nernstian and non-nernstian behaviours and a diffusional model was used to treat the chronopotentiometric data. Thermodynamic (potential, concentration) and kinetic parameters (diffusion coefficient) were successfully determined for the redox system studied in this work.