Zintl Ions within Framework Channels: The Complex Structure and Low-Temperature Transport Properties of NaGe.

Single crystals of a complex Zintl compound with the composition NaGe were synthesized for the first time using a high-pressure/high-temperature approach. Single-crystal diffraction of synchrotron radiation revealed a hexagonal crystal structure with P6/m space group symmetry that is composed of a three-dimensional sp Ge framework punctuated by small and large channels along the crystallographic c axis. Na atoms are inside hexagonal prism-based Ge cages along the small channels, while the larger channels are occupied by layers of disordered sixfold Na rings, which are in turn filled by disordered [Ge] tetrahedra.

Ambient-Pressure Polymerization of Carbon Anions in the High-Pressure Phase Mg2C.

Experimental and theoretical methods were employed to investigate the ambient-pressure, metastable phase transition pathways for Mg2C, which was recovered after high-pressure synthesis. We demonstrate that at temperatures above 600 K isolated C(4-) anions within the Mg2C structure polymerize into longer-chain carbon polyanions, resulting in the formation of the α-Mg2C3 (Pnnm) structure, which is another local energy minimum for the carbon-magnesium system. Access to the thermodynamic ground state (decomposition into graphite) was achieved at temperatures above ∼1000 K.

Synthesis of an open-framework allotrope of silicon.

Silicon is ubiquitous in contemporary technology. The most stable form of silicon at ambient conditions takes on the structure of diamond (cF8, d-Si) and is an indirect bandgap semiconductor, which prevents it from being considered as a next-generation platform for semiconductor technologies. Here, we report the formation of a new orthorhombic allotrope of silicon, Si24, using a novel two-step synthesis methodology.

Synthesis and structural characterization of Na(x)Si136 (0 < x ≤ 24) single crystals and low-temperature transport of polycrystalline specimens.

Na(x)Si(136) clathrate-II single crystals with x = 2.9, 5.1, 8.