La liaison metal-metal dans les clusters M12O36: I - Preparation et etude structurale des phases La4M6O19 (M = Ru,Os)

La₄Ru₆O₁₉ and La₄Os₆O₁₉ are prepared for the first time by the oxidation of stoechiometric mixtures of (La₂O₃ + RuO₂) and (La₂O₃ + Os) with excess KC10₃. The crystal structure of both compounds are solved by conventional Fourier and least-squares methods to R = 0.022 and R = 0.024, respectively, using automated four-circle diffractometer data. Both are isostructural with La₄Re₆O₁₉. M-M distances (2.488 Å for M = Ru and 2.499 Å for M = Os) show evidence of strong metal-metal interaction. Comparison of data for M = Ru, Os or Re reveals the evolution of some interatomic distances with Z.