Langmuir-Blodgett films based on inorganic molecular complexes with magnetic or optical properties

Langmuir and Langmuir-Blodgett (LB) films of a great variety of molecular metal complexes with interesting magnetic or optical properties have been prepared in the last few years. Some of the results obtained by our group and others are summarized in this article. (i) LB films of polyoxometalates (POM) were first prepared taking advantage of the adsorption properties of these cluster anions along a positively charged monolayer of an organic surfactant spread in water. A correct choice of the POM allowed the preparation of LB films with magnetic, electrochromic, or luminescent properties. Besides this semiamphiphilic method, two new methods to prepare LB films of POMs have been developed by other groups: one is based on the replacement of the charge-balancing counter-ions of the POMs salts by cationic surfactants. With this method luminescent LB films have been prepared. The other method is based on the synthesis of a bis(alkyl) substituted amphiphilic POM. (ii) LB films of the Mn-12 single-molecule magnets were prepared from mixtures of the benzoate and acetate derivatives of Mn12 with behenic acid. These magnetic films showed a marked hysteresis loop in the magnetization below 5 K. (iii) Magnetic LB multilayers of two ferritin molecules, containing 4220 and 3062 Fe atoms have been prepared. Magnetic measurements have shown that the superparamagnetic properties of these molecules are preserved. Thus, a marked hysteresis loop of magnetization has been observed in these films below 15 K. (c) 2005 Elsevier B.V. All rights reserved.