Ternary alkali metal transition metal acetylides

Abstract

The first alkali metal transition metal acetylides of general composition A2M0C2 (A = Na - Cs, M0 = Pd, Pt) were obtained by solid state reactions of alkali metal acetylides with palladium and platinum. They are characterized by ∞1[M 0(C2)2/22-] chains, which are separated by alkali metal ions. Analogous ∞I[M I(C2)2/2-] chains also separated by alkali metal ions are the characteristic structural feature of acetylides of composition AMIC2, which are accessible by reacting AC2H with M1I in liquid ammonia (A = Li - Cs, M I = Cu, Ag, Au). Despite their structural similarities they possess different properties, as acetylides of composition A2M 0C2 are semiconductors with very small indirect band gaps and slightly extended C-C distances compared to a C-C triple bond, whereas acetylides of composition AMIC2 show a typical salt-like behavior with C-C distances close to the expected value for a C-C triple bond of 120 pm. But with the help of simple chemical models these differences can be made plausible. Furthermore, it is shown that only by a combination of different methods (powder diffraction with X-rays and neutrons, solid state NMR spectroscopy, Raman spectroscopy) it was possible to characterize this new class of compounds structurally and chemically. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.