Carbon-boron clathrates as a new class of sp(3)-bonded framework materials

Carbon-based frameworks composed of sp(3) bonding represent a class of extremely lightweight strong materials, but only diamond and a handful of other compounds exist despite numerous predictions. Thus, there remains a large gap between the number of plausible structures predicted and those synthesized. We used a chemical design principle based on boron substitution to predict and synthesize a three-dimensional carbon-boron framework in a host/guest clathrate structure. The clathrate, with composition 2Sr@B6C6, exhibits the cubic bipartite sodalite structure (type VII clathrate) composed of sp(3)-bonded truncated octahedral C12B12 host cages that trap Sr2+ guest cations. The clathrate not only maintains the robust nature of diamond-like sp(3) bonding but also offers potential for a broad range of compounds with tunable properties through substitution of guest atoms within the cages.