Leonard Brian M, Schaak Raymond E
Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012, USA.
J Am Chem Soc. 2006 Sep 6;128(35):11475-82. doi: 10.1021/ja062475h.
Understanding how solids form is a challenging task, and few strategies allow for the elucidation of reaction pathways that are useful for designing new solids. Here, we describe an unusual multistep reaction pathway that leads to the formation of AuCuSn(2), a new ternary intermetallic compound that was discovered as nanocrystals using a low-temperature solution route. The formation of AuCuSn(2) using a modified polyol process occurs through a multistep pathway that was elucidated by taking aliquots throughout the course of the reaction and studying the products using a variety of techniques. The reaction proceeds through four distinct steps: (a) formation of Au nanoparticles at or near room temperature, mediated by a galvanic reaction between Au(3+) and Sn(2+) (forming Au(0) and Sn(4+), precipitated as SnO(2) that forms a shell around the nanoparticles), (b) formation of NiAs-type AuSn nanoparticles, along with Cu and Sn, upon addition of NaBH(4), (c) aggregation and thermal interdiffusion to form AuCu(x)Sn(y) alloy nanoparticles, and (d) nucleation of intermetallic AuCuSn(2), which has an ordered NiAs-derived structure. The proposed mechanism was tested by starting the reaction with the AuSn intermediate. AuSn nanoparticles were synthesized separately and reacted with Cu and Sn nanoparticles, and ordered AuCuSn(2) formed as expected. Elucidation of this reaction pathway has important implications for guiding the design of new intermetallic solids, as well as for controlling the synthesis of complex multimetal nanocrystals.
理解固体如何形成是一项具有挑战性的任务，而且很少有策略能够阐明对设计新固体有用的反应途径。在此，我们描述了一种不同寻常的多步反应途径，该途径导致了AuCuSn₂的形成，AuCuSn₂是一种新的三元金属间化合物，它是通过低温溶液法作为纳米晶体被发现的。使用改良的多元醇工艺形成AuCuSn₂是通过一个多步途径进行的，该途径是通过在反应过程中取等分试样并使用多种技术研究产物而阐明的。反应通过四个不同的步骤进行：(a) 在室温或接近室温下由Au³⁺和Sn²⁺之间的电化学反应介导形成Au纳米颗粒（形成Au⁰和Sn⁴⁺，以SnO₂的形式沉淀，在纳米颗粒周围形成壳层），(b) 添加NaBH₄后形成NiAs型AuSn纳米颗粒以及Cu和Sn，(c) 聚集和热互扩散形成AuCuₓSnᵧ合金纳米颗粒，以及(d) 具有有序NiAs衍生结构的金属间化合物AuCuSn₂的成核。通过以AuSn中间体开始反应来测试所提出的机制。分别合成AuSn纳米颗粒并使其与Cu和Sn纳米颗粒反应，预期形成有序的AuCuSn₂。阐明该反应途径对于指导新型金属间固体的设计以及控制复杂多金属纳米晶体的合成具有重要意义。
