Novel carbonyl iron–bismuth clusters – synthesis, structure, CO 2 insertion and potential as molecular precursors for BiFeO 3

Abstract

The reaction of Fe 2(CO) 9 with Bi(OSiMe 2 tBu) 3 gave soluble [(CO) 4FeBi(OSiMe 2 tBu)] 2 ( 1) in moderate yield whereas in case of Bi(O tBu) 3 used as starting material both [(CO) 4FeBi(O tBu)] n ( 2) and the bismuth–iron cluster [(CO) 3FeBi 3(O tBu) 4{OCO(O tBu)}] 2 ( 3) were isolated. The latter forms upon insertion of CO 2, released during reaction of diiron nonacarbonyl with bismuth tert-butoxide, into a Bi–O tBu bond. The compounds were characterized by IR and 1H 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) 4FeBi(OSiMe 2 tBu)] 2 ( 1) is build up by a four-membered Bi 2Fe 2 ring whereas [(CO) 3FeBi 3(O tBu) 4{OCO(O tBu)}] 2 ( 3) is composed of two tetrahedral FeBi 3 cluster cores that dimerise via bridging –OCO(O tBu) ligands. Analysis of the TGA residues by PXRD revealed that compound 2 is the best precursor for multiferroic BiFeO 3 among the compounds studied here, although Bi 25FeO 39 was detected as minor impurity.