Active Nature of Primary Amines during Thermal Decomposition of Nickel Dithiocarbamates to Nickel Sulfide Nanoparticles
Active Nature of Primary Amines during Thermal Decomposition of Nickel Dithiocarbamates to Nickel Sulfide Nanoparticles
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DOI：
10.1021/cm503174z
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发表时间：
2014-11-11
影响因子：
8.6
通讯作者：
de Leeuw, Nora H.
中科院分区：
文献类型：
--
作者：
Hollingsworth, Nathan;Roffey, Anna;de Leeuw, Nora H.
虽然[Ni（S2 CNBu 2 i）（2）]在高温下在一系列溶剂中是稳定的，但在145 ℃下在油胺中发生溶剂热分解，得到纯NiS纳米颗粒，而在120 ℃下在正己胺中得到Ni 3S 4（polydymite）和NiS的混合物。一个相结合的实验和理论研究给出了分解过程的机理洞察，可以用来解释所观察到的差异。在伯胺中溶解后，八面体反式-[Ni（S2 CNBu 21）（2）（RNH 2）（2）]的结果如通过原位XANES和EXAFS所示并通过DFT计算证实。加热至90-100 ℃导致与酰胺交换产物[Ni（S2 CNBu（2）（i））{S2 CN（H）R}]和/或[Ni{S2 CN（H）R}（2）]的形成一致的变化。DFT建模表明，交换通过伯胺在二硫代氨基甲酸酯配体的主链碳上的亲核攻击而发生。使用己胺，酰胺交换是容易的，并且在分解之前形成显著量的[Ni{S2 CN（H）Hex}（2）]，但是使用油胺，交换较慢，并且[Ni（S2 CNBu 21）{S2 CN（H）Oleyl}]是活性反应组分。伯胺二硫代氨基甲酸盐络合物在约20 ℃下迅速分解。在100 ℃下，即使在不存在伯胺的情况下，也可以得到硫化镍，如[Ni{S2 CN（H）Hex}（2）]的热分解研究所示。[Ni{S2 CN（H）R}（2）]的DFT模拟表明，质子从氮迁移到硫导致形成二硫代氨基甲酸酯（S2 C-NR），其失去异硫氰酸酯（RNCS），得到二聚硫醇镍络合物[Ni{S2 CN（H）R}（mu-SH）]（2）。这些中间体可以失去二硫代氨基甲酸酯或挤出进一步的异硫氰酸酯以提供（可能是胺稳定的）硫醇镍结构单元，其聚集以得到观察到的硫化镍纳米颗粒。可以区分单或双酰胺交换产物的分解，因此酰胺交换的不同速率主要导致所观察到的纳米颗粒硫化镍的形成。
Although [Ni(S2CNBu2i)(2)] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145 degrees C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120 degrees 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(S2CNBu2i)(2)(RNH2)(2)] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90-100 degrees C leads to changes consistent with the formation of amide-exchange products, [Ni(S2CNBu(2)(i)){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(S2CNBu2i){S2CN(H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100 degrees 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}(mu-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.