Two New Arsenides, Eu₇Cu₄₄As₂₃ and Sr₇Cu₄₄As₂₃, With a New Filled Variety of the BaHg₁₁ Structure

Two new ternary arsenides, namely, Eu₇Cu₄₄As₂₃ and Sr₇Cu₄₄As₂₃, were synthesized from elements at 800 °C. Their crystal structure represents a new filled version of the BaHg₁₁ motif with cubic voids alternately occupied by Eu­(Sr) and As atoms, resulting in a 2 × 2 × 2 superstructure of the aristotype: space group Fm3̅m, a = 16.6707(2) Å and 16.7467(2) Å, respectively. The Eu derivative exhibits ferromagnetic ordering below 17.5 K. In agreement with band structure calculations both compounds are metals, exhibiting relatively low thermopower, but high electrical and low thermal conductivity.