High Pressure Synthesis of Marcasite-Type Rhodium Pernitride

Marcasite-type rhodium nitride was successfully synthesized in a direct chemical reaction between a rhodium metal and molecular nitrogen at 43.2 GPa using a laser-heated diamond-anvil cell. This material shows a low zero-pressure bulk modulus of <i>K</i>₀ = 235(13) GPa, which is much lower than those of other platinum group nitrides. This finding is due to the weaker bonding interaction between metal atoms and quasi-molecular dinitrogen units in the marcasite-type structure, as proposed by theoretical studies

Possible Superhardness of CrB₄

Chromium tetraboride [orthorhombic, space group <i>Pnnm</i> (No. 58), <i>a</i> = 474.65(9) pm, <i>b</i> = 548.0(1) pm, <i>c</i> = 286.81(5) pm, and <i>R</i> value (all data) = 0.041], formerly described in space group <i>Immm</i>, was found not to be superhard, despite several theory-based prognoses. CrB₄ shows an almost temperature-independent paramagnetism, consistent with low-spin Cr^I in a metallic compound. Conductivity measurements confirm the metallic character