Multilayer graphane synthesized under high hydrogen pressure
A new hydrocarbon hydrographite with the composition close to CH is shown to form from graphite and gaseous hydrogen at pressures above 2 GPa and temperatures from 450 to 700 degC. Hydrographite is a black solid thermally stable under ambient conditions. When heated in vacuum, it decomposes into graphite and molecular hydrogen at temperatures from 500 to 650 degC. Powder X ray diffraction characterizes hydrographite as a multilayer "graphane II" phase predicted by ab initio calculations [Wen X D et al. PNAS 2011; 108:6833] and consisting of graphane sheets in the chair conformation stacked along the hexagonal c axis in the ABAB sequence. The crystal structure of the synthesized phase belongs to the P63mc space group. Moreover, the unit cell parameters are a 2.53(1) A and c 9.54(1) A and therefore exceed the corresponding parameters of graphite by 2.4(2) and 42.0(3) Stretching vibrations of C H groups on the surface of the hydrographite particles are examined by infrared spectroscopy.