Dumbbells of Five-Connected Silicon Atoms and Superconductivity in the Binary Silicides MSi₃ (M = Ca, Y, Lu)

The new metastable binary silicides MSi₃ (M = Ca, Y, Lu) have been synthesized by high-pressure, high-temperature reactions at pressures between 12(2) and 15(2) GPa and temperatures from 900(100) to 1400(150) K. The atomic patterns comprise intricate silicon layers of condensed molecule-like Si₂ dimers. The alkaline-earth element adopts the oxidation state +2, while the rare-earth and transition metals realize +3. All of the compounds exhibit BCS-type superconductivity with weak electron–phonon coupling below critical temperatures of up to 7 K