Controlling the Minimal Self Assembly of “Complex” Polyoxometalate Clusters

Despite
the vast number of polyoxometalate clusters now known,
an ongoing and important challenge is to understand causality in the
assembly of “complex” clusters at a mechanistic level,
since this is the only way the rational, targeted synthesis of new
compounds will ever be achieved. Often, the complexity of the reactions
themselves makes such investigations near impossible, as very small
changes can often make dramatic differences. Herein, we explore a
very simple [A + B] binary synthetic system that gives rise to the
facile assembly of two isomeric anions, [FeIII(H2O)2{γ-FeIIISiW9O34(H2O)}2]11– (1) and [FeIII(H2O)2{γ-FeIII2SiW8O33(H2O)2}­{γ-SiW10O35}]11– (2), which can be formed as individual and dimeric
species (3) and (4). Furthermore, the simple
binary nature of this synthetic system allowed its investigation by
a comprehensive time-resolved ESI-MS analysis, yielding unprecedented
mechanistic information regarding the initial interactions and reorganizations
of the {γ-SiW10} precursor in the presence of Fe2+.

尽管目前已发现的多金属氧簇（polyoxometalate clusters）数量众多，但从机理层面解析“复杂”簇合物组装过程中的因果关系仍是一项持续存在且至关重要的挑战——唯有如此，方能实现新化合物的理性定向合成。通常，反应体系本身的复杂性使得此类研究几乎难以开展，因为极细微的条件变化往往会引发显著的结果差异。本文中，我们针对一种极为简单的[A+B]二元合成体系展开研究，该体系可便捷组装出两种异构阴离子：[FeIII(H2O)2{γ-FeIIISiW9O34(H2O)}2]11–（标记为1）与[FeIII(H2O)2{γ-FeIII2SiW8O33(H2O)2}­{γ-SiW10O35}]11–（标记为2），二者可分别以单体（3）与二聚体（4）的形式存在。此外，该合成体系的简单二元特性，使得我们能够通过全面的时间分辨电喷雾电离质谱（time-resolved electrospray ionization mass spectrometry, ESI-MS）分析对其进行研究，从而获得了{γ-SiW10}前驱体在Fe²+存在下的初始相互作用与重组过程的前所未有的机理信息。