The Synthesis of New Compounds Containing Metal Clusters Using Designed Superlattice Reactants to Control the Kinetics and Reaction Mechanism

这个建议的重点是合成新的三元过渡金属硫族化合物，它含有离散的过渡金属原子簇。三元钼硫族化物和富勒烯的碱金属插入物都是这类化合物的例子，它们含有离散但相互作用的簇实体。这两类材料都被发现具有许多不寻常的性质，从催化活性到超导性，这些性质由于这些材料中发现的独特簇结构而被合理化。目的是制备钨、铌和钽化合物，它们是三元硫族钼的等结构类似物。三元钼化合物的等结构和等电子化合物的制备将允许对这些基于结构的论点进行测试，并有望扩展在这类独特材料中发现的性质范围，这在某种意义上弥合了离散分子化合物和扩展结构之间的差距。在低温下涉及固体的化学反应是非常缓慢的，尽管通常有很大的推动力。以前试图通过元素之间的反应制备新的三元过渡金属硫族化合物，这些化合物含有离散的过渡金属原子簇，只产生二元化合物或其他三元结构的混合物。这可能是因为期望的化合物相对于这些相图中的已知化合物在热力学上是不稳定的。因此，成功合成它们的关键是避免形成稳定的二元化合物作为反应中间体。为此，基于元素超晶格作为独特的可定制反应物的设计，开发了一条动力学控制的固态化合物路线。这种方法分离了固态反应的两个关键步骤——反应物的相互扩散和产物的成核。由于产物的形成是由发光势垒控制的，因此可以从动力学上控制产物的形成。开发合成工具使所需结构成核是拟议研究的重要组成部分。

9510562 Johnson This proposal focuses upon the synthesis of new ternary transition metal chalcogenides which contain discrete clusters of transition metal atoms. The ternary molybdenum chalcogenides and the alkali metal intercalates of the fullerines are both examples of this class of compounds, containing discrete but interacting cluster entities. Both of these classes of materials have been found to have a host of unusual properties ranging from catalytic activity to superconductivity which have been rationalized as resulting from the unique cluster structure found in these materials. The goal is to prepare tungsten, niobium and tantalum compounds which are isostructural analogs of the ternary molybdenum chalcogenides. The preparation of isostructural and isoelectronic compounds to the ternary molybdenum compounds will permit the testing of these structure based arguments and will hopefully extend the range of properties found in this unique class of materials which is some sense bridges the gap between discrete molecular compounds and extended structures . %%% Chemical reactions involving solids at low temperatures are very sluggish even though there is often a large driving force for the reactions. Previous attempts to prepare new ternary transition metal chalcogenides which contain discrete clusters of transition metal atoms via reactions between the elements have only produced mixtures of binary compounds or other ternary structures. This is probably because the desired compounds are thermodynamically unstable with respect to the known compounds in these phase diagrams. Consequently, the key to the success to their synthesis will be avoiding the formation of stable binary compounds as reaction intermediates. Towards this end, a kinetically controlled route to solid-state compounds is developed based upon the design of elemental superlattices as uniquely tailorable reactants. This approach separates the two key steps of a solid state reaction - interdi ffusion of the reactants and nucleation of the products. Since product formation is controlled by the lucleation barriers, one is able to kinetically control the product formed. The development of synthetic tools to nucleate desired structures is a significant part of the proposed research.