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 degrees C. Hydrographite is a black solid thermally stable under ambient conditions. If heated in vacuum, it decomposes into graphite and molecular hydrogen at temperatures from 500 to 650 degrees C. 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 P6(3)mc space group. The unit cell parameters are a = 2.53(1) angstrom c = 9.54(1) angstrom 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. (C) 2015 Published by Elsevier Ltd.