Neue Arsenide mit ThCr₂Si₂- oder einer damit verwandten Struktur: Die Verbindungen ARh₂As₂ (A: Eu, Sr, Ba) und BaZn₂As₂ / New Arsenides with ThCr₂Si₂-type or Related Structures: The Compounds ARh₂As₂ (A: Eu, Sr, Ba) and BaZn₂As₂

Four new arsenides of rhodium and zinc were prepared by heating mixtures of the elements at high temperatures (1000 - 1200 °C) and investigated by single crystal X-ray methods. EuRh₂As₂ (a = 4.067(1), c = 11.319(2) Å ) and BaRh₂As₂ (a = 4.053(1), c = 12.770(3) Å ) crystallize with the well-known ThCr₂Si₂-type (I4/mmm; Z = 2). Due to the rigid layers of RhAs₄ tetrahedra, and to the atomic size of europium and barium, the As-As distances between the layers with values of 2.97 and 3.66 Å, respectively, are very long. SrRh₂As₂ is polymorphic and undergoes two phase transitions at about 190 and 282 °C. Main features of the three crystal structures are also layers of RhAs₄ tetrahedra. At room temperature α-SrRh₂As₂ (a = 5.676(1), b = 6.178(2), c = 11.052(2) Å ) probably crystallizes with the BaNi₂Si₂-type (Cmcm; Z = 4), whereas β -SrRh2As2 (a = 5.760(3), b = 6.067(4), c = 11.264(5) A° , Fmmm, Z = 4) forms a new orthorhombically distorted variant of the ThCr₂Si₂-type. Single crystals grown in a flux of lead and quenched at high temperature show that the γ -phase (a = 4.112(1), c = 11.431(6) Å ) crystallizes with the ThCr₂Si₂-type. The same is true for the high temperature modification of BaZn₂As₂ (β -phase; a = 4.120(1), c = 13.578(1) Å ), whereas the already known α-BaZn₂As₂ forms the α-BaCu₂S₂-type (Pnma; Z = 4) consisting of a 3D-network of edge- and vertex-sharing ZnAs₄ tetrahedra with Ba atoms in the voids of this network.