Novel carbonyl iron-bismuth clusters - synthesis, structure, CO2 insertion and potential as molecular precursors for BiFeO3

The reaction of Fe-2(CO)(9) with Bi((OSiMe2Bu)-Bu-t)(3) gave soluble [(CO)(4)FeBi((OSiMe2Bu)-Bu-t)](2) (1) in moderate yield whereas in case of Bi(OtBu)(3) used as starting material both [(CO)(4)FeBi(OtBu)](n) (2) and the bismutheiron cluster [(CO)(3)FeBi3(OtBu)(4){OCO(OtBu)}](2) (3) were isolated. The latter forms upon insertion of CO2, released during reaction of diiron nonacarbonyl with bismuth tert-butoxide, into a Bi-(OBu)-Bu-t bond. The compounds were characterized by IR and H-1 NMR spectroscopy as well as thermogravimetric analyses. Additionally, the molecular structures of compounds 1 and 3 were elucidated by single crystal X-ray diffraction. The core structure of [(CO)(4)FeBi((OSiMe2Bu)-Bu-t)](2) (1) is build up by a four-membered Bi2Fe2 ring whereas [(CO)(3)FeBi3((OBu)-Bu-t)(4){OCO(OtBu)}](2) (3) is composed of two tetrahedral FeBi3 cluster cores that dimerise via bridging -OCO(OtBu) ligands. Analysis of the TGA residues by PXRD revealed that compound 2 is the best precursor for multiferroic BiFeO3 among the compounds studied here, although Bi25FeO39 was detected as minor impurity. (C) 2011 Published by Elsevier B. V. t