Department of Chemistry, The University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA.
Department of Materials Science and Engineering, The University of California, Davis, One Shields Avenue, Davis, CA, 95616, USA.
Angew Chem Int Ed Engl. 2017 Feb 20;56(9):2418-2422. doi: 10.1002/anie.201611510. Epub 2017 Jan 18.
A new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba M P (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra common to clathrates along with a unique 22-vertex polyhedron with two hexagonal faces capped by additional partially occupied phosphorus sites. This is the first example of a clathrate compound where the framework atoms are not in tetrahedral or trigonal-pyramidal coordination. In Ba M P a majority of the framework atoms are five- and six-coordinated, a feature more common to electron-rich intermetallics. The crystal structure of this new clathrate was determined by a combination of X-ray and neutron diffraction and was confirmed with solid-state P NMR spectroscopy. Based on chemical bonding analysis, the driving force for the formation of this new clathrate is the excess of electrons generated by a high concentration of Zn atoms in the framework. The rattling of guest atoms in the large cages results in a very low thermal conductivity, a unique feature of the clathrate family of compounds.
在 Ba/Cu/Zn/P 体系中发现了一种新的笼型化合物。BaMP（M=Cu/Zn）笼型化合物的晶体结构由笼型化合物共有的正五边形十二面体和独特的 22 个顶点多面体组成，其中两个六方面由额外的部分占据磷位封顶。这是第一个骨架原子不是四面体或三角双锥配位的笼型化合物的例子。在 BaMP 中，大多数骨架原子是五配位和六配位的，这是富电子金属间化合物的一个特征。这种新型笼型化合物的晶体结构是通过 X 射线和中子衍射相结合确定的，并通过固态磷 NMR 光谱得到证实。基于化学键分析，形成这种新型笼型化合物的驱动力是框架中高浓度 Zn 原子产生的过剩电子。大笼中客体原子的摇晃导致极低的热导率，这是笼型化合物家族的独特特征。
