Journal of Electroanalytical Chemistry 454 (1998) 91 – 97 Electrochemical study of ferrocene and nitroxide derivatives intercalated in Zn–Cr and Zn–Al layered double hydroxides S. Therias a , B. Lacroix a , B. Scho ¨ llhorn a , C. Mousty a, *, P. Palvadeau b a Laboratoire d’Electrosynthe `se et d’Electroanalyse Bioorganique, SEESIB-UMR 6504, Uniersite ´ Blaise Pascal, 63177 Aubiere cedex, France b IMN-Chimie des Solides, UMR 110, BP 32229, 44322 Nantes Cedex 3, France Received 23 February 1998; received in revised form 5 June 1998 Abstract Layered double hydroxides (LDH) containing the electrochemical redox anions ferrocene sulfonates (FcMS and FcDS) and a nitroxide radical (NODC) have been prepared and characterized by PXRD, IR and ESR. The electrochemical behaviour of these hybrid materials as well as the role of the electrolyte anions during the oxidation process have been studied by cyclic voltammetry. An electrochemical transfer at LDH modified electrodes via an intracrystallite mechanism is confirmed. © 1998 Elsevier Science S.A. All rights reserved. Keywords: LDH modified electrodes; Anionic clays; Ferrocene sulfonate; Nitroxide 1. Introduction In the last 20 years, research arose focusing on the preparation and the characterization of electrodes modified with inorganic structured materials such as zeolites and clays [1–3]. Most of the studies on clay modified electrodes have been done with swelling cationic clays known as smectite clays. Since 1987, several publications report on the use of synthetic hy- drotalcite-like clays such as layered double hydroxides (LDH) in the preparation of electrodes. Inorganic elec- troactive species [4 – 7] as well as organic molecules bearing anionic groups have been incorporated [8 – 11]. In particular, we have made a structural and electro- chemical characterization of LDH exchanged with or- ganic electroactive anions bearing a sulfonate group, such as nitrobenzene sulfonate, anthraquinone mono- and disulfonate [8] and 2,2-azinobis(3-ethylbenzothia- zoline-6-sulfonate) (ABTS) [9,10]. In this paper, we report the intercalation in LDH of ferrocene mono- and disulfonate and a nitroxide free radical bearing anionic groups. The electrochemical properties of these intercalated compounds, known as good redox media- tors, are studied by cyclic voltammetry. 2. Experimental Sodium or ammonium salts of the monosulfonic and disulfonic ferrocene (FcMS and FcDS) were obtained by direct sulfonation of ferrocene with chlorosulfonic acid following the method described by Knox and Pauson [12]. The resulting sulfonate derivatives were further recrystallized from methanol and ethanol re- spectively and characterized by FTIR, 1 H NMR spec- troscopies and mass spectroscopy. The 1 H NMR spectrum of the sodium salt of FcMS showed three singlets at 4.10 (2H), 4.25 (5H) and 4.35 (2H) ppm. With FcDS, the 1 H NMR spectrum presents two sin- glets at 4.2 (4H) and 4.4 (4H) and a broad signal at 7.2 (8H, NH 4 + ) ppm. In both cases IR spectra showed absorption bands at 1650 cm -1 and in the region 1000–1100 cm -1 corresponding to the ferrocene moi- * Corresponding author. Fax: +33 47 3274443; e-mail: mousty@cicsun.univ-bpclermont.fr 0022-0728/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0022-0728(98)00273-3