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Active nature of primary amines during thermal decomposition of nickel dithiocarbamates to nickel sulfide nanoparticles

Hollingsworth, Nathan, Roffey, Anna, Islam, Husn-Ubayda, Mercy, Maxime, Roldan Martinez, Alberto, Bras, Wim, Wolthers, Mariette, Catlow, Charles, Sankar, Gopinathan, Hogarth, Graeme and de Leeuw, Nora H. 2014. Active nature of primary amines during thermal decomposition of nickel dithiocarbamates to nickel sulfide nanoparticles. Chemistry of Materials 26 (21) , pp. 6281-6292. 10.1021/cm503174z

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Although [Ni(S2CNBui 2)2] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145 °C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120 °C a mixture of Ni3S4 (polydymite) and NiS results. A combined experimental and theoretical study gives mechanistic insight into the decomposition process and can be used to account for the observed differences. Upon dissolution in the primary amine, octahedral trans- [Ni(S2CNBui 2)2(RNH2)2] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90−100 °C leads to changes consistent with the formation of amide-exchange products, [Ni(S2CNBui 2){S2CN(H)R}] and/or [Ni{S2CN(H)R}2]. DFT modeling shows that exchange occurs via nucleophilic attack of the primary amine at the backbone carbon of the dithiocarbamate ligand(s). With hexylamine, amide-exchange is facile and significant amounts of [Ni{S2CN(H)Hex}2] are formed prior to decomposition, but with oleylamine, exchange is slower and [Ni(S2CNBui 2){S2CN- (H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100 °C to afford nickel sulfides, even in the absence of primary amine, as shown from thermal decomposition studies of [Ni{S2CN(H)Hex}2]. DFT modeling of [Ni{S2CN(H)R}2] shows that proton migration from nitrogen to sulfur leads to formation of a dithiocarbimate (S2CNR) which loses isothiocyanate (RNCS) to give dimeric nickel thiolate complexes [Ni{S2CN(H)R}(μ-SH)]2. These intermediates can either lose dithiocarbamate(s) or extrude further isothiocyanate to afford (probably amine-stabilized) nickel thiolate building blocks, which aggregate to give the observed nickel sulfide nanoparticles. Decomposition of the single or double amide-exchange products can be differentiated, and thus it is the different rates of amideexchange that account primarily for the formation of the observed nanoparticulate nickel sulfides.

Item Type: Article
Date Type: Published Online
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: American Chemical Society
ISSN: 0897-4756
Last Modified: 21 Feb 2019 14:21

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