SYNTHETIC, STRUCTURAL AND SPECTROSCOPIC STUDIES OF HETERONUCLEAR (OXO)ALKOXIDES AS PRECURSORS FOR M I XED-M ETAL OXI DES Giovana G. Nunes, 1 Dayane M. Reis, 1 Pedro H. C. Camargo, 1 Peter B. Hitchcock, 2 Eduardo L. Sá, 1 David J. Evans, 3 Carlos J. da Cunha, 1 Germano Tremiliosi-Filho, 4 Aldo J. G. Zarbin, 1 and Jaísa F. Soares *1 , 1 Departamento de Química, Universidade Federal do Paraná, Centro Politécnico, Jardim das Américas, 81531-990 - Curitiba-PR, Brazil 2 Department of Chemistry, University of Sussex, Falmer, Brighton BN1 9QJ, England 3 Department of Biological Chemistry, John Innes Centre, Colney Lane, Norwich NR4 7UH, England 4 Departamento de Físico-Química, Instituto de Química de São Carlos, Universidade de São Paulo, 13560-970, São Carlos-SP, Brazil. (Received May 2005) Abstract: Polymetallic alkoxides have been used as precursors for semi-conducting, ferroelectric, dielectric, thermo- and electrochromic oxide materials which present a wide range of technological applications. In the last 5-10 years, we have been interested in the structural features and reactivity patterns of single-source alkoxide precursors (SSP), that is, molecules containing different metal elements in well-defined stoichiometric proportions, and also in their sol-gel processing to give the related mixed-metal oxides. We already reported the first examples of structurally-characterised double alkoxides of Ti/Fe, V/K and V/Fe, as well as homonuclear analogues. All products were characterised by a number of techniques including Mössbauer and EPR spectroscopies, magnetic moment measurements and single crystal X-ray diffractometry. Quantum mechanical calculations by semiempirical and ab initio methods were also carried out. Complexes containing both titanium and iron were prepared by reaction of [Ti(OPr i )4] with KOPr i in toluene, followed by the addition of FeCln (n = 2, 3). Preparations involving iron(II) gave [FeCl{Ti2(OPr i )9}] (A) and [Ti3(OMe)2(OPr i )9][Fe4TiCl4(O)(OPr i )9] (B). With FeCl3, products were [FeCl2(Pr i OH)4] (C), [Ti3(OPr i )11][FeCl4] (D) and [Fe5(m5-O)(m-OPr i )8Cl5] (E). Complex D was probably produced by a redox reaction between propan-2-ol and iron(III). Reactions involving vanadium(IV) starting materials, on the other hand, gave high yields of thermochromic [V2(m-OPr i )2(OPr i )6] (F). Complex F has been employed as a molecular precursor of heterometal alkoxides containing non-oxo V IV , as the one obtained by the reaction between F and [Fe2(m-I)2I2(HOPr i )4] (G) in toluene/propan-2-ol. This gave the novel mixed-metal [FeI2(m-OPr i )2V(OPr i )2(HOPr i )] (H). Sol-gel synthesis from the single-source precursor A, followed by heat treatment at 300-1000 o C, gave a mixture of rutile-TiO2 and pseudobrookite (Fe2TiO5), as indicated by Mössbauer, FTIR, EPR and Raman spectroscopies, powder XRD and SEM/EDS data. Based on these results, the synthesis of new molecules containing iron, vanadium and titanium in different stoichiometric proportions, aiming at the preparation of specific mixed-metal oxides, as well as the preparation and characterisation of thin films produced from F and H, are now under way in our laboratory at UFPR. Key words: alkoxide, heteronuclear, metal oxides, single-source precursor, sol-gel. 1. INTRODUCTION Mixed-metal oxides are an important class of advanced materials employed in coatings, surfaces, sensors and devices, with well-known applications in catalysis, optics and electronics. 1-5 They can been classified into (i) multiphase oxides, such as in TiO 2 -WO 3 or NdAlO3-Al2O3 systems; 6-7 (ii) solid solutions, such as (Ti,Sn)O2 8 and (iii) pure heterometal oxides, such as BaTiO3, FeVO4 or YFeO3. 9-11 Many of these materials have been synthesised from mixtures of single metal precursors, either by conventional solid state or by solution methods. 12 In these mixtures, reaction rates for distinct precursors Metals Materials And Processes, 2005, Vol. 17, No. 3-4, pp. 343 - 362. © Meshap Science Publishers, Mumbai, India. * Corresponding author; E-Mail: jaisa@quimica.ufpr.br