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

The reaction of Fe2(CO)9 with Bi(OSiMe2tBu)3 gave soluble [(CO)4FeBi(OSiMe2tBu)]2 (1) in moderate yield whereas in case of Bi(OtBu)3 used as starting material both [(CO)4FeBi(OtBu)]n (2) and the bismuth–iron cluster [(CO)3FeBi3(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–OtBu 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(OSiMe2tBu)]2 (1) is build up by a four-membered Bi2Fe2 ring whereas [(CO)3FeBi3(OtBu)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.

Graphical abstractThe reaction of Fe2(CO)9 with Bi(OSiMe2tBu)3 and Bi(OtBu)3, respectively, was studied to give iron–bismuth clusters. In case of the bismuth silanolate a tetranuclear compound, [(CO)4FeBi(OSiMe2tBu)]2 (1), was observed, whereas reaction with bismuth tert-butoxide gave an octanuclear complex as crystalline main product, [(CO)3FeBi3(OtBu)4{OCO(OtBu)}]2 (3), which is formed as a result of CO2 insertion into bismuth alkoxide bonds. The molecular structures of the compounds as well as their thermal behaviour was studied.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Novel iron–bismuth clusters isolated and structurally characterized. ► Metal–bismuth bonds. ► CO2 insertion into bismuth alkoxide bond. ► Compounds of this type are potentially useful as precursors for the synthesis of multiferroic BiFeO3.