Novel arachno-type X-5(6-) zintl anions in Sr3Sn5,Ba3Sn5, and Ba3Pb5 and charge influence on Zintl clusters

Two new binary Zintl phases, Sr3Sn5 and Ba3Sn5 were synthesized and structu rally characterized. The revised structure of Ba3Pb5 is also reported. All three compounds are isotypic and crystallize with a modified Pu3Pd5 structu re type. The anionic substructure is composed Of X-5(6-) square pyramidal c lusters (X = Sn, Pb), which are described as arachno clusters according to the Wade-Mingos electron counting rules. The electronic structure of the py ramidal Zintl anions and the influence of the number of skeletal electrons of these clusters are investigated using the electron localization function (ELF). The structural relationship between Ba3Sn5 and the Zintl phases Ba3 Si4 and Ba3Ge4 are analyzed. Additionally, two new Zintl phases Ba3Ge2.82Sn 2.18 and Ba3Ge3.94Sn0.06, have been synthezised and their structures are re ported, which directly show that the exchange of tin against germanium lead s to a change from the M3X5 to the M3X4 structure type. This effect is trac ed back to the maximal charge acquisition property of the Zintl anions of h eavier and lighter tetralides.