New siloxane-containing iron(III) carboxylate clusters

New complexes of the composition: {Fe3O(OOCR1COO)3}+ and {Fe3O(R2COO)6}+, where R1 = –(CH2)3–Si(CH3)2–O–Si(CH3)2–(CH2)3– or –(CH2)8–COO–CH2–Si(CH3)2–O–Si(CH3)2–CH2–COO–(CH2)8–; R2 = Si(CH3)3–O–Si(CH3)2–CH2–COO–(CH2)8–, were synthesized by direct synthesis using siloxane carboxylic salts and iron nitrate or by ligand exchange in μ3-oxo trinuclear iron(III) acetoxy-cluster with siloxane carboxylic acids. The obtained compounds have been characterized by elemental analysis, FT–IR and UV–Vis spectroscopy, mass spectrometry (ESI–MS), thermal analysis, Mössbauer spectroscopy, and magnetic measurements. By ESI–MS, in the starting iron acetate dodecanuclear cluster was detected besides the trinuclear compound. The new siloxane-containing iron(III) clusters showed a bathochromic shift in UV–Vis spectra compared to the acetate. The thermal decomposition starts above 200 °C and higher thermal stability was observed for the clusters with sebaco-siloxane diacid. The Mössbauer spectroscopy data indicate the presence of iron(III) in a high spin state. By using a potassium salt of sebacomethylpentamethyldisiloxane as a reactant and stabilizer, iron cluster nanoparticles were obtained, both by direct synthesis and ligand exchange. According to all our data, the direct synthesis is a more convenient reaction path, in terms of reaction conditions and purity of the final products.