Expanding the Toolbox: Synthesis of Zintl Salts Containing Anions of the In/Sb and Tl/Sb Elemental Combinations

Binary Zintl anions comprising atoms of two p-block elements, and ternary Zintl clusters, in which the latter are combined with d-/f-block metal ions, are being studied with great activity. However, although an impressive variety of elemental compositions have been realized, some combinations of the p-block (semi)metals are lacking in corresponding substructures. The In/Sb combination is extremely rare, and Tl/Sb has not yet been realized at all, although the existence of pseudo-tetrahedral species, for instance, was predicted by quantum chemical studies. Extraction of the novel ternary phase K6InSb3 and of K6Tl2Sb3 with ethane-1,2-diamine (en) yielded binary Zintl anions of these elemental combinations as salts comprising pseudo-tetrahedral anions (InSb3)2– and (TlSb3)2– or nine-vertex cages (In4Sb5)3– and (Tl4Sb5)3–, respectively. To establish efficient synthesis routes, the extractions were monitored using electrospray-ionization mass spectrometry and fractionated crystallization. We thereby isolated salts of two further anions that might represent intermediates on the way to larger species, namely, a novel salt of the Sb73– anion, and a salt of the new binary anion (TlSb7)2–. We describe the experimental approach, the process of its optimization, the geometric structures of the new compounds as well as their electronic structures that were established by DFT calculations.