Three Inter‐Alkali Metal Acetylides: KNaC 2 , KRbC 2 , and NaRbC 2 : Syntheses, Crystal Structures, and Structural Systematics

Three alkali metal acetylides, namely KNaC 2 , KRbC 2 , and NaRbC 2 , were synthesized and characterized by means of X‐ray powder diffraction. KNaC 2 and KRbC 2 crystallize as a variant of the anti ‐PbCl 2 ‐type structure ( Pnma , Z = 4), whereas NaRbC 2 crystallizes as a variant of the anti ‐PbFCl‐type structure ( Pmmn , Z = 2). Based on a simple systematic approach developed by Sabrowsky et al. for inter‐alkali metal chalcogenides all known inter‐alkali metal acetylides can be classified into two classes: variants of the anti ‐PbCl 2 type structure and variants of the anti ‐PbFCl type structure. Acetylides with Q (ABC 2 ) ≤ 1.45 crystallize in the anti ‐PbCl 2 ‐type structure, whereas for Q (ABC 2 ) > 1.45 the anti ‐PbFCl‐type structure is found ( Q ( AB C 2 ) = V m ( A 2 C 2 )/ V m ( B 2 C 2 ) with V m ( A 2 C 2 ) > V m ( B 2 C 2 ); V m : molar volume, A , B = alkali metals).