Ca 14 FeAs 11 – A structure comprising structural motifs of iron‐based superconductors and Ca‐As Zintl phases

Ca 14 FeAs 11 is the first iron‐containing representative of the Ca 14 AlSb 11 structure type and the first compound with isolated FeAs 4 tetrahedra. It can be regarded as a salt‐like compound containing isolated [FeAs 4 ] 9− tetrahedra, linear [As 3 ] 7− units, isolated As 3− anions and Ca 2+ cations and thus is a borderline compound between binary Fe−As intermetallics and salt‐like calcium arsenides. Ca 14 FeAs 11 is obtained by a two‐step high‐temperature reaction, in which preformed FeAs alloy is heated with Ca in the presence of additional As in a sealed silica tube. Structure determination from single crystals at 150 K reveal the Ca 14 AlSb 11 structure type with space group I 4 1 / acd ( Z =8, a =15.6268(2) Å, c =20.9781(5) Å, and V =5122.79(15) Å 3 ). Band structure calculations predict metallic properties with strong contribution of Fe orbitals to the density of states at the Fermi level.