RESUMO
In the systems Ba/Mg/(Si, Ge), two new ternary Zintl phases with the compositions BaMg(4)Si(3) and BaMg(4)Ge(3) were found and structurally characterized. Both compounds are isotypic and crystallize with a new structure type [BaMg(4)Si(3), P4/mmm, Z = 1, a = 4.6115(9) Å, c = 8.615(2) Å; BaMg(4)Ge(3), P4/mmm, Z = 1, a = 4.6335(8) Å, c = 8.746(2) Å]. The anionic partial structure is built of X(2)(6)(-) dumbbells and isolated X(4)(-) ions (X = Si, Ge), and the structure can be described according to the Zintl-Klemm-Busmann concept with the formulation (Ba(2+))(Mg(2+))(4)[X(2)(6)(-)][X(4)(-)]. The BaMg(4)X(3) structure can also be described as a result of the fusion of the structures of Mg(2)X and BaMg(2)X(2). In this regard, BaMg(4)Si(3) and BaMg(4)Ge(3) are very striking examples of chemical twinning.
RESUMO
Polymerizations in single crystals have rarely been described-in the case of the title compound they are even reversible. The rebuttoning of the bonds can be regarded as bond stretching isomerism, which is currently the subject of controversial discussion in many areas of chemistry. The geometrical arrangement of the monomeric Ge46- ions in the crystal is shown in the picture.
