Three Inter‐Alkali Metal Acetylides: KNaC2, KRbC2, and NaRbC2: Syntheses,Crystal Structures,and Structural Systematics

Three alkali metal acetylides, namely KNaC₂, KRbC₂, and NaRbC₂, were synthesized and characterized by means of X‐ray powder diffraction. KNaC₂ and KRbC₂ crystallize as a variant of the anti‐PbCl₂‐type structure (Pnma, Z = 4), whereas NaRbC₂ 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‐PbCl₂ type structure and variants of the anti‐PbFCl type structure. Acetylides with Q(ABC₂) ≤ 1.45 crystallize in the anti‐PbCl₂‐type structure, whereas for Q(ABC₂) > 1.45 the anti‐PbFCl‐type structure is found (Q(ABC₂) = V_m(A₂C₂)/V_m(B₂C₂) with V_m(A₂C₂) > V_m(B₂C₂); V_m: molar volume, A, B = alkali metals).