Lucky Number 13: A 13-Layer Polytype of the Alkyne Hydrogenation Catalyst CaGaGe.

Polytypism, the ability of materials to form crystal structures with different stacking sequences, occasionally causes materials with the same stoichiometry and similar local structures to have profoundly different properties. Herein, we discover a metastable 13-layer trigonal (13T) polytype of CaGaGe, a layered intermetallic phase comprised of [GaGe] honeycombs separated by Ca. 13T-CaGaGe is synthesized from arc-melting the elements, and its structure is elucidated via neutron powder diffraction.

Alkyne Hydrogenation Catalysis across a Family of Ga/In Layered Zintl Phases.

Transition-metal-free Zintl-Klemm phases have received little attention as heterogeneous catalysis. Here, we show that a large family of structurally and electronically similar layered Zintl-Klemm phases built from honeycomb layers of group 13 triel (Tr) or group 14 tetrel (Tt) networks separated by electropositive cations (A) and having a stoichiometry of ATr or ATrTt (A = Ca, Ba, Y, La, Eu; Tr = Ga, In; Tt = Si, Ge) exhibit varying degrees of activity for the hydrogenation of phenylacetylene to styrene and ethylbenzene at 51 bar H and 40-100 °C across a variety of solvents. The most active catalysts contain Ga with, formally, a half-filled p orbital, and minimal bonding between neighboring Tr or TrTt layers.

Transition Metal-Free Alkyne Hydrogenation Catalysis with BaGa, a Hydrogen Absorbing Layered Zintl Phase.

Inexpensive, transition metal-free intermetallic compounds have received almost no attention as heterogeneous catalysts. Here, we show that BaGa, a Zintl-Klemm compound composed of honeycomb sheets of Ga anions separated by Ba cations and known to react with H under moderate conditions to form a layered polyanionic hydride BaGaH, effectively catalyzes the hydrogenation of phenylacetylene into styrene and ethylbenzene under modest conditions (1-50 bar H, 40-100 °C). Remarkably, the catalytic activity of BaGa (surface specific activities up to 8390 h) is on the same order of magnitude as commercial Pd-based catalysts.