Active Nature of Primary Amines during Thermal Decomposition of Nickel Dithiocarbamates to Nickel Sulfide Nanoparticles
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- 作者：Nathan Hollingsworth ; Anna Roffey ; Husn-Ubayda Islam ; Maxime Mercy ; Alberto Roldan ; Wim Bras ; Mariette Wolthers ; C. Richard A. Catlow ; Gopinathan Sankar ; Graeme Hogarth ; Nora H. de Leeuw
- 刊名：Chemistry of Materials
- 出版年：2014
- 出版时间：November 11, 2014
- 年：2014
- 卷：26
- 期：21
- 页码：6281-6292
- 全文大小：695K
- ISSN：1520-5002
文摘
Although [Ni(S2CNBui2)2] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145 掳C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120 掳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(S2CNBui2)2(RNH2)2] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90鈥?00 掳C leads to changes consistent with the formation of amide-exchange products, [Ni(S2CNBui2){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(S2CNBui2){S2CN(H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100 掳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鈺怤R) which loses isothiocyanate (RNCS) to give dimeric nickel thiolate complexes [Ni{S2CN(H)R}(渭-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 amide-exchange that account primarily for the formation of the observed nanoparticulate nickel sulfides.