Abstract
Nanoparticulate iron sulfides have many potential applications and are also proposed to be prebiotic catalysts for the reduction of CO2 to biologically important molecules, thus the development of reliable routes to specific phases with controlled sizes and morphologies is important. Here we focus on the use of iron dithiocarbamate complexes as single source precursors (SSPs) to generate greigite and pyrrhotite nanoparticles. Since these minerals contain both iron(iii) and iron(ii) centres, SSPs in both oxidation states, [Fe(S2CNR2)3] and cis-[Fe(CO)2(S2CNR2)2] respectively, have been utilised. Use of this Fe(ii) precursor is novel and it readily loses both carbonyls in a single step (as shown by TGA measurements) providing an in situ source of the extremely air-sensitive Fe(ii) dithiocarbamate complexes [Fe(S2CNR2)2]. Decomposition of [Fe(S2CNR2)3] alone in oleylamine affords primarily pyrrhotite, although by careful control of reaction conditions (ca. 230 °C, 40–50 nM SSP) a window exists in which pure greigite nanoparticles can be isolated. With cis-[Fe(CO)2(S2CNR2)2] we were unable to produce pure greigite, with pyrrhotite formation dominating, a similar situation being found with mixtures of Fe(ii) and Fe(iii) precursors. In situ X-ray absorption spectroscopy (XAS) studies showed that heating [Fe(S2CNiBu2)3] in oleylamine resulted in amine coordination and, at ca. 60 °C, reduction of Fe(iii) to Fe(ii) with (proposed) elimination of thiuram disulfide (S2CNR2)2. We thus carried out a series of decomposition studies with added thiuram disulfide (R = iBu) and found that addition of 1–2 equivalents led to the formation of pure greigite nanoparticles between 230 and 280 °C with low SSP concentrations. Average particle size does not vary significantly with increasing concentration, thus providing a convenient route to ca. 40 nm greigite nanoparticles. In situ XAS studies have been carried out and allow a decomposition pathway for [Fe(S2CNiBu2)3] in oleylamine to be established; reduction of Fe(iii) to Fe(ii) reduction triggers substitution of the secondary amide backbone by oleylamine (RNH2) resulting in the in situ formation of a primary dithiocarbamate derivative [Fe(RNH2)2(S2CNHR)2]. This in turn extrudes RNCS to afford molecular precursors of the observed FeS nanomaterials. The precise role of thiuram disulfide in the decomposition process is unknown, but it likely plays a part in controlling the Fe(iii)–Fe(ii) equilibrium and may also act as a source of sulfur allowing control over the Fe : S ratio in the mineral products.
Highlights
ADepartment of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK bDepartment of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK cNetherlands Organisation for Scienti c Research DUBBLE@ESRF, 38043 Grenoble, France dChemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA eSchool of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK † Dedicated to the memory of Professor Paul O'Brien CBE FRS FREng FRSC (1954–2018) an outstanding person and talented chemist who pioneered the use of dithiocarbamate complexes as single source precursors. ‡ Electronic supplementary information (ESI) available
The resulting black powder was dissolved in 100 mL of CH2Cl2 and stirred with magnesium sulphate for 30 min, a er which it was ltered and the ltrate dried in vacuo
The resulting black powder was dissolved in 100 mL of CH2Cl2 and stirred with magnesium sulphate for 30 min, a er which the mixture was ltered and the ltrate dried in vacuo
Summary
ADepartment of Chemistry, King's College London, Britannia House, 7 Trinity Street, London SE1 1DB, UK bDepartment of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ, UK cNetherlands Organisation for Scienti c Research DUBBLE@ESRF, 38043 Grenoble, France dChemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA eSchool of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK † Dedicated to the memory of Professor Paul O'Brien CBE FRS FREng FRSC (1954–2018) an outstanding person and talented chemist who pioneered the use of dithiocarbamate complexes as single source precursors. ‡ Electronic supplementary information (ESI) available. [Fe(S2CNMe2)3] (1a).[54] NaS2CNMe2 (4.30 g, 30 mmol) in water (60 mL) was added dropwise to a solution of FeCl3 (1.62 g, 10 mmol) in water (50 mL), whereupon a black precipitate formed. The resulting black powder was dissolved in 100 mL of CH2Cl2 and stirred with magnesium sulphate for 30 min, a er which it was ltered and the ltrate dried in vacuo. To this mixture CS2 (1.80 mL, 30 mmol) was added dropwise over 10 min and the mixture stirred overnight.
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