Carbon nanotubes have shown great success on the research of fuel cell, battery, supercapacitor, lightweight electrical conductors, flexible electronics and heaters. Inspired by carbon nanotubes, scientists also create a lot of other crystalline inorganic nanotube arrays. However, they are limited in oxides and chalcogenides. It is still a big challenge to prepare well-defined inorganic nanotube array with other elements. Teams from state key laboratory of structural chemistry have gained insight into the metal halide nanotube. Their research has been published on January 11^th 2016 in Angew. Chem. Int. Ed., and was chosen as Frontispiece.

They synthesized the metal halide crystalline inorganic nanotube for the first time. The [Pb^II₁₈I₅₄(I₂)₉] wheels are integrated with each other in face-to-face manner by the I-I covalent bonds to form [Pb^II₁₈I₅₄(I₂)₉]_n nanotube with a crystallographic 6₃ screw axis running through the center of the nanotube. Up to now, Wheel cluster shows much diversity and tunability on its structure: metal can be V, Mo, Cr, W, Nb et al, that are limited in polyoxometalates and chalcogenide. The electrical properties of this nanotube based on single-crystal were also studied and show significantly anisotropic semiconductive behavior. Under room temperature, the conductivity along the nanotube is about 1 order of magnitude higher than that perpendicular to the nanotube, which further increases to ~2 orders of magenitude at 180 ^oC. The conductivity also shows anisotropic temperature effect: from room temperature to 180 ^oC, the conductivity along the nanotube increases with the value of ~3 orders of magnitude, while the conductivity perpendicular to the nanotube increases only ~2 orders of magnitude.

From the help of Beijing Synchrotron Radiation Facility (BSRF), they gained the whole structure of the nanotube. And found that the wheel cluster [Pb^II₁₈I₅₄(I₂)₉] was constructed by six Pb₃I₁₃ trimers linking with each other end-to-end in D₃ symmetry, with the outer diameter of 2.53 nm and the inner diameter of about 1.32 nm. This is the biggest metal halide wheel cluster. The wheel cluster connected by I-I covalent bonds to form [Pb^II₁₈I₅₄(I₂)₉]_n nanotube. Isolated (Pb^II₂I₉)^5？ cluster, I^– ions, propylated (Pr₂DABCO)²⁺ dications, and lattice water molecules are filling in and out the nanotubes.    

Because of huge electron number disparity between inorganic iodoplumbate and organic Pr₂DABCO²⁺, it is difficult to determine the organic part by normal lab X-ray instrument. Synchrotron X-ray diffraction helped to gain the whole single crystal structure successfully. 

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