Friedfeld Max R, Stein Jennifer L, Ritchhart Andrew, Cossairt Brandi M
Department of Chemistry , University of Washington , Seattle , Washington 98195 , United States.
Acc Chem Res. 2018 Nov 20;51(11):2803-2810. doi: 10.1021/acs.accounts.8b00365. Epub 2018 Nov 2.
Clusters are unique molecular species that can be viewed as a bridge between phases of matter and thus between disciplines of chemistry. The structural and compositional complexity observed in cluster chemistry serves as an inspiration to the material science community and motivates our search for new phases of matter. Moreover, the formation of kinetically persistent cluster molecules as intermediates in the nucleation of crystals makes these materials of great interest for determining and controlling mechanisms of crystal growth. Our lab developed a keen interest in clusters insofar as they relate to the nucleation of nanoscale semiconductors and the modeling of postsynthetic reaction chemistry of colloidal materials. In particular, our discovery of a structurally unique InPX (X = carboxylate) cluster en route to InP quantum dots has catalyzed our interest in all aspects of cluster conversion, including the use of clusters as precursors to larger nanoscale colloids and as platforms for examining postsynthetic reaction chemistry. This Account is presented in four parts. First, we introduce cluster chemistry in a historical context with a focus on main group, metallic, and semiconductor clusters. We put forward the concept of rational, mechanism-driven design of colloidal semiconductor nanocrystals as the primary motivation for the studies we have undertaken. Second, we describe the role of clusters as intermediates both in the synthesis of well-known material phases and in the discovery of unprecedented nanomaterial structures. The primary distinction between these two approaches is one of kinetics; in the case of well-known phases, we are often operating under high-temperature thermolysis conditions, whereas for materials discovery, we are discovering strategies to template the growth of kinetic phases as dictated by the starting cluster structure. Third, we describe reactions of clusters as model systems for their larger nanomaterial progeny with a primary focus on cation exchange. In the case of InP, cation exchange in larger nanostructures has been challenging due to the covalent nature of the crystal lattice. However, in the higher energy, strained cluster intermediates, cation exchange can be accomplished even at room temperature. This opens opportunities for accessing doped and alloyed nanomaterials using postsynthetically modified clusters as single-source precursors. Finally, we present surface chemistry of clusters as the gateway to subsequent chemistry and reactivity, and as an integral component of cluster structure and stability. Taken as a whole, we hope to make a compelling case for using clusters as a platform for mechanistic investigation and materials discovery.
团簇是独特的分子物种，可被视为物质相之间的桥梁，从而也是化学各学科之间的桥梁。团簇化学中观察到的结构和组成复杂性激发了材料科学界的灵感，并促使我们探索新的物质相。此外，动力学稳定的团簇分子作为晶体成核过程中的中间体形成，使得这些材料对于确定和控制晶体生长机制非常有意义。就团簇与纳米级半导体的成核以及胶体材料的合成后反应化学建模的关系而言，我们实验室对团簇产生了浓厚兴趣。特别是，我们在合成InP量子点的过程中发现了一种结构独特的InPX（X = 羧酸盐）团簇，这激发了我们对团簇转化各个方面的兴趣，包括将团簇用作更大纳米级胶体的前体以及用作研究合成后反应化学的平台。本综述分为四个部分。首先，我们在历史背景下介绍团簇化学，重点是主族、金属和半导体团簇。我们提出了合理的、由机制驱动的胶体半导体纳米晶体设计概念，作为我们所开展研究的主要动机。其次，我们描述团簇在合成已知材料相以及发现前所未有的纳米材料结构中作为中间体的作用。这两种方法的主要区别在于动力学方面；对于已知相，我们通常在高温热解条件下进行操作，而对于材料发现，我们正在探索策略，按照起始团簇结构的要求来引导动力学相的生长。第三，我们将团簇的反应描述为其更大纳米材料后代的模型系统，主要关注阳离子交换。就InP而言，由于晶格的共价性质，在更大的纳米结构中进行阳离子交换一直具有挑战性。然而，在能量更高、应变的团簇中间体中，即使在室温下也可以实现阳离子交换。这为使用合成后修饰的团簇作为单源前体来制备掺杂和合金化的纳米材料提供了机会。最后，我们介绍团簇的表面化学，它是后续化学和反应性的通道，也是团簇结构和稳定性的一个组成部分。总体而言，我们希望能有力地证明将团簇用作机理研究和材料发现的平台。
