Structure and stability of hydrogen clathrates of ammonia borane

Structural rules have been formulated for the molecular crystal of ammonia borane (AB, NH₃BH₃) and clathrates thereof. These rules are similar to the "ice rules" in water. Periodic structures of possible clathrates of AB have been predicted. A rigorous analysis of the uniform space filling tessellations of 3D space has been performed resulting in the identification of two promising structures for AB clathrates. Additional five structures have been identified exploiting features and properties of AB molecules. The screening, or evaluation, of proposed periodic structures has been performed on the basis of their stability determined at the density functional level of theory. Hydrogen capacity of the most stable periodic structure (cantitruncated cubic honeycomb) is estimated to be 21 wt%, 19% chemically bound in AB and 2 wt% of H₂ physisorbed in the cages of AB. © 2010 Materials Research Society.