Geometrical Frustration of B-H Bonds in Layered Hydrogen Borides Accessible by Soft Chemistry

Hydrogen borides adopt a variety of structures because of the electron-deficient character of boron. Recently, we reported the synthesis of a layered hydrogen boride via a soft chemical route. Here, we ascertain the atomic arrangements in the layered hydrogen boride by using pair-distribution functions: the material dominantly consists of a corrugated B network decorated with three-center, two-electron B-H-B bridging bonds as well as ordinary two-center, two-electron B-H terminal bonds. The material is locally ordered but amorphous by diffractometry. This discrepancy can be accounted for by geometrical frustration caused by the positions of terminal B-H bonds located on one of two equivalent B atoms in the B-H-B bridging bonds. This material is electrically conductive (0.13 S cm(-1) below 10 degrees C) rather than ion conductive, and its B-H-B bonds are cleaved by the adsorption of molecules; this dynamic chemical nature originates from the frustrated structure and leads to unique hydrogen boride functionalities.