Between Elemental Match and Mismatch: From K12Ge3.5Sb6 to Salts of (Ge2Sb2)2−, (Ge4Sb12)4−, and (Ge4Sb14)4−

Abstract

The solid mixture “K2GeSb” was shown to comprise single-crystalline K12Ge3.5Sb6 (1), a double salt of K5[GeSb3] with carbonate-like [GeSb3]5− anions, and the metallic Zintl phase K2Ge1.5. Extraction of 1 with ethane-1,2-diamine in the presence of crypt-222 afforded [K(crypt-222)]+ salts of several novel binary Zintl anions: (Ge2Sb2)2− (in 2), (Ge4Sb12)4− (in 3), and in the presence of [AuMePPh3] also (Ge4Sb14)4− (in 4). The anion in 2 represents a predicted, yet heretofore missing pseudo-tetrahedral anion. 4 comprises a cluster analogous to (Ge4Bi14)4− and (Ga2Bi16)4−, and thus one of the most Sb-rich binary p-block anions. The unprecedented cluster topology in 3 can be viewed as a defect-version of the one in 4 upon following a “dead end” of cluster growth. The findings indicate that Ge and Sb atoms are at the border of a well-matching and a mismatch elemental combination. We discuss the syntheses, the geometric structures, and the electronic structures of the new compounds.