Introduction Solid-state reactions are generally very slow processes as a consequence of the negligible diffusion rate of chemical species in solids. To circumvent this drawback, the most frequently used expedient is to employ finely milled powders and to increase the temperature up to 1,000– 1,500°C. However, recently the use of nanoparticle dis- persions in reversed micellar solutions has been sug- gested as a novel route allowing fast solid-state reactions without the need for drastic and economically disad- vantageous working conditions [1, 2]. In particular, for the synthesis of inorganic salts, the proposed method consists of the following steps: i) entrapment of appropriate amounts of the selected re- agent salt in the hydrophilic core of the water-containing reversed micelles dispersed in apolar solvent, ii) com- plete evaporation of volatile components (water and apolar solvent) of the salt-containing system, iii) resus- pension of the salt/surfactant composite in apolar sol- vent leading to the formation of dry dispersions of salt nanoparticles coated by opportunely oriented surfactant molecules [3, 4], and iv) mixing of two appropriate dry dispersions of nanoparticle containing reversed micelles. C. Giordano A. Longo A. Ruggirello V. Turco Liveri A. M. Venezia Physicochemical investigation of cobalt–iron cyanide nanoparticles synthesized by a novel solid–solid reaction in confined space Received: 19 December 2003 Accepted: 22 March 2004 Published online: 24 April 2004 Ó Springer-Verlag 2004 Abstract Cobalt–iron cyanide (Co x [Fe(CN) 6 ]) nanoparticles have been synthesized by a novel solid– solid reaction in the confined space of dry sodium bis(2-ethylhexyl)sul- fosuccinate (AOT) reversed micelles dispersed in n-heptane. The reaction has been carried out by mixing two dry AOT/n-heptane solutions con- taining CoCl 2 and K 4 Fe(CN) 6 or K 3 Fe(CN) 6 nanoparticles in the micellar core, respectively. By UV- Vis spectroscopy it was ascertained that, after the mixing process, the formation of stable nanoparticles is fast and complete. Microcalorimet- ric measurements of the thermal ef- fect due to the Co x [Fe(CN) 6 ] nanoparticle formation allowed the determination of the stoichiometric ratio (x) and of the molar enthalpy of reaction in the core of AOT re- versed micelles. The observed behavior suggests the occurrence of confinement effects and surfactant adsorption on the nanoparticle sur- face. Further structural information was achieved by small-angle X-ray scattering (SAXS) measurements. From all liquid samples, interesting salt/AOT composites were prepared by simple evaporation of the apolar solvent. Size, crystal structure, and electronic properties of Co x [Fe(CN) 6 ] nanoparticles con- taining composites were obtained by wide-angle X-ray scattering (WAXS) and X-ray photoelectron spectroscopy (XPS). Keywords Cobalt–iron cyanide complexes Æ Nanoparticles Æ Solid– solid reaction Æ Confinement effect Æ AOT reversed micelles Colloid Polym Sci (2004) 283: 265–276 DOI 10.1007/s00396-004-1124-1 ORIGINAL CONTRIBUTION C. Giordano Æ A. Ruggirello V. Turco Liveri (&) Department of Physical Chemistry, Universita` di Palermo, Viale delle Scienze Parco D’Orleans II, 90123 Palermo, Italy E-mail: turco@unipa.it A. Longo Æ A. M. Venezia ISMN, Istituto per lo Studio dei Materiali Nanostrutturati, Via U. La Malfa 153, 90146 Palermo, Italy