Crystal Structures of Homoleptic Propynyloargentates A I [Ag(C 3 H 3 ) 2 ] with A I = Ag, Li, Na Solved and Refined from X‐ray Powder Diffraction Data

The crystal structures of three isostructural homoleptic propynyloargentates, namely Ag[Ag(C 3 H 3 ) 2 ], Li[Ag(C 3 H 3 ) 2 ], and Na[Ag(C 3 H 3 ) 2 ] were solved and refined from laboratory X‐ray powder diffraction data ( Iba 2, Z = 4). Almost linear [H 3 C–C≡C ··· Ag ··· C≡C–CH 3 ] – anions are found: The alkali metal cations or the second silver cation coordinate side‐on to the C≡C triple bond of the alkyne ligand (CN = 8) so that layer‐like structural fragments are formed, which are stacked in an AB fashion along [100]. These crystal structures are corroborated by IR and solid‐state NMR spectra. Powder SHG measurements confirm the acentric space group Iba 2. On the other hand, these methods also supported a first structural model obtained earlier, in which very unusual bent [Ag(CCCH 3 ) 2 ] – units were found in a smaller unit cell ( Amm 2, Z = 2). Bond‐analytical COHP calculations clearly indicate that this structural motif cannot be stable. A close re‐inspection of the diffraction data, now also including high‐resolution synchrotron powder diffraction data (HASYLAB, beamline B2), reveal the existence of one weak additional reflection indicating a larger unit cell. Hence, this investigation clearly shows that under very specific circumstances – e.g. ligands with a weak scattering power compared to the central metal ion – wrong structural models can be obtained from X‐ray powder diffraction data, even when additional information from complementary spectroscopic methods is taken into account. Additional electronic‐structure calculations are therefore needed to elucidate the correct structural arrangement.