Layered hydroxide metal acetates (metal ) zinc, cobalt, and nickel) have been prepared by a new route belonging to the chimie douce method. This novel method involves the hydrolysis, in polyol medium, of in situ-formed complexes supposed to be alkoxyacetates. These layered hydroxide metal acetates present poorly ordered character, and their X-ray patterns have features typical of lamellar compounds with turbostratic disorder. Their chemical formula was established to be M(OH) 2-x (CH 3 COO) x ‚nH 2 O with (x, n) ) (0.42, 0.31), (0.38, 0.53), and (0.40, 0.63) for Zn, Co, and Ni, respectively. The layered hydroxide nickel acetate has a classical brucite structure with a random substitution of some hydroxyl groups by acetate groups. The layered hydroxide zinc and cobalt acetates are isomorphous with the hydrozincite structure, in which cations are located in both octahedral and tetrahedral sites. The acetate anion behaves as a unidentate ligand in LHS-Ni and LHS-Co, where LHS indicates layered hydroxide salt, and is intercalated as a free anion in the zinc compound. The dehydration is a reversible topotactic process for LHS-Ni and Co, whereas it is a destructive process in the case of LHS-Zn.

Fine CoFe 2 O 4 powders with monodisperse, almost equi-axial nanometer-sized particles were synthesised in a polyol medium by forced hydrolysis of ionic Co(II) and Fe(III) salts at 160 ³C. K(Co) XANES and 57 Fe Mo È ssbauer spectroscopy show that the structure of this ferrite is slightly deviated from an inverse spinel structure: 16% of cobalt atoms are in tetrahedral sites. The particles are superparamagnetic above 300 K and ferrimagnetic below this blocking temperature with, at low temperature, strong coercivity, a saturation magnetisation value close to the bulk value and high reduced remanence. The saturation magnetisation measured at 5 K is clearly enhanced with respect to CoFe 2 O 4 nanometer-sized particles previously prepared by other methods. These magnetic characteristics suggest that these particles have a high crystallinity which may result from this novel synthesis route.{Basis of a presentation given at Materials Discussion No.

Layered nickel hydroxide salts Ni(OH) 22x (A) x ?nH 2 O (A ~NO 3 2 , n-alkylsulfonates C n H 2n11 SO 3 2 with n ~10, 14, 18) have been prepared by exchange reaction in aqueous medium at pH ~8.5, starting from the layered hydroxide acetate Ni(OH) 1.5 (CH 3 COO) 0.5 ?nH 2 O. This parent compound has been synthesized by hydrolysis in polyol medium. The obtained compounds present the typical features of the brucite-like structure with turbostratic disorder and an interlayer spacing varying in the range 7.5-32 A ˚. The magnetic properties have been investigated by means of dc and ac measurements. Two main interactions are found in these materials. On one hand, ferromagnetic in-plane exchange interactions dominate at high temperature, as deduced from the positive Weiss constant, while interlayer ferromagnetic interactions of dipolar origin are responsible for the 3D order at low temperature. This order is indicated by the hysteresis loops below a critical temperature lying in the range 16-18 K. The magnetic properties will be discussed in relation to the structural features, and are mainly driven by the length of the intercalated anion and its head-group functionality. It will be shown that these compounds form a novel series of layered materials for which the model of ferromagnetic layers interacting through dipolar coupling can be successfully applied.