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Breaking the Tetra‐Coordinated Framework Rule: New Clathrate Ba 8 M 24 P 28+ δ ( M =Cu/Zn)
Author(s) -
Dolyniuk JuliAnna,
Zaikina Julia V.,
Kaseman Derrick C.,
Sen Sabyasachi,
Kovnir Kirill
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201611510
Subject(s) - clathrate hydrate , dodecahedron , crystallography , chemistry , crystal structure , neutron diffraction , intermetallic , hydrate , organic chemistry , alloy
A new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba 8 M 24 P 28+ δ ( 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 8 M 24 P 28+ δ 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 31 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.