Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding.
Ligand exchange and the stoichiometry of metal chalcogenide nanocrystals: spectroscopic observation of facile metal-carboxylate displacement and binding.
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DOI：
10.1021/ja4086758
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发表时间：
2013-12-11
影响因子：
15
通讯作者：
Owen JS
中科院分区：
文献类型：
--
作者：
Anderson NC;Hendricks MP;Choi JJ;Owen JS
我们证明了金属羧酸盐络合物（L-M（O2 CR）2，R =油烯基，十四烷基，M = Cd，Pb）容易从羧酸根封端的ME纳米晶体中置换（ME = CdSe，CdS，PbSe，PbS）通过各种刘易斯碱（L =三正丁胺、四氢呋喃、十四醇、N，N-二甲基-正丁胺、三正丁基膦、N，N，N ′，N ′-四甲基丁烯-1，4-二胺、吡啶、N，N，N ′，N '-四甲基亚乙基-1，2-二胺，正辛胺）。通过1H NMR光谱测量相对置换效力，并且最强烈地取决于几何因素，如空间位阻和螯合，尽管也取决于与镉离子的硬/软匹配。结果表明，配体取代L-M（O2 CR）2通过协同络合的位移金属离子以及的双金属离子。从CdSe和CdS纳米晶体中去除高达90%的表面结合的Cd（O2 CR）2将Cd：Se比从1.1 ± 0.06降低到1.0 ± 0.05，加宽1 Se-2S 3/2 h吸收，并将光致发光量子产率（PLQY）从10%降低到<1%（CdSe）和20%降低到<1%（CdS）。这些变化在室温下重新结合M（O2 CR）2时部分逆转（约60%），在升高的温度下完全逆转。提出了一种模型，其中电子接受M（O2 CR）2配合物（Z型配体）可逆地结合到纳米晶体导致一个范围内的化学计量对于一个给定的核心大小。结果表明，纳米晶体缺乏单一的化学式，而是具有浓度依赖性成分的动态结构。这些发现的重要性，纳米晶体的合成和纯化以及配体交换反应进行了讨论。
We demonstrate that metal carboxylate complexes (L–M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by 1H NMR spectroscopy and depends most strongly on geometric factors like sterics and chelation, though also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L–M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd:Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1Se-2S3/2h absorption and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (~60 %) and fully reversed at elevated temperature. A model is proposed where electron accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.
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