Rich Non-centrosymmetry in a Na–U–Te Oxo-System Achieved under Extreme Conditions

Two new sodium uranyl tellurites
and two new sodium uranyl tellurates have been synthesized from high-temperature/high-pressure
conditions and structurally characterized. We demonstrated that crystalline
phases, forming in a Na–U–Te system under extreme conditions,
appear to favorably have non-centrosymmetric structures. Three out
of four novel uranyl tellurium compounds, Na­[(UO2)­TeIV2O5(OH)], Na2[(UO2)­(TeVI2O8)], and Na2[(UO2)­TeVIO5], crystallize in non-centrosymmetric
space groups. The crystal structure of Na­[(UO2)­TeIV2O5(OH)] is based on two-dimensional [UO2Te2O5(OH)]− corrugated
sheets, which are charge balanced by guest Na+ cations.
The structure of Na2[(UO2)­TeVI2O8] is constructed from [(UO2)2Te2O8]2+ anionic layers composed
of UO7 pentagonal bipyramids and TeO6 octahedra.
Na2[(UO2)­(TeVIO5)] is
a new type of three-dimensional anionic open framework built from
the interconnection of UO7 pentagonal bipyramids and TeO6 octahedra with different types of interlacing channels within
the U–Te anionic framework. Na­[(UO2)­TeIV6O13(OH)], as the only centrosymmetric
compound isolated in the Na–U–Te family, is crystallized
in space group Pa3̅, and its structure is highly
related to that of cliffordite (UO2(Te3O7)), which is composed from UO8 hexagonal bipyramids
and TeO5 square pyramids. The vibrational modes associated
with U–O, TeIV–O, and TeVI–O
bonds are discussed, and the Raman spectra of the four compounds are
characterized for signature bands.