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 Sb₇^3- 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.