A Linear, Trinuclear, Mixed-Valence Chloro Complex of Ruthenium, [RugCln]4-

Upon addition of tetraethylammonium chloride to the deep blue solution obtained by dissolving Ru₂(O₂CCH₃)₄Cl in 12 M hydrochloric acid, followed by evaporation in an argon atmosphere, a deep green, crystalline product is isolated. X-ray crystallographic study has defined this substance as [(C₂H₅)₄N]₂[H₇O₃]₂[Ru₃Cl₁₂]. The complex aniort, which resides on a crystallographic inversion center, may be described as a linear array of three RuCU octahedra in which the central one shares two opposite triangular faces with the outer ones. The total of the oxidation numbers of the ruthenium atoms is +8 and from the symmetry it appears that the outer metal atoms are each Ru^III and the central one Ru11. The Ru-Ru distances are 2.805 (1) Å and the octahedra are only slightly distorted-The compound crystallizes in space group P2c with unit cell dimensions of a = 9.542 (2) Å, 6 = 14.940 (2) Å, c= 14.403 (2) Å, β = 104.97 (1)°, and V= 1984 (1) ų, with 2 = 2. With all nonhydrogen atoms treated anisotropically and hydrogen atoms omitted, the structure was refined to R₁ = 0.050 and R₂ = 0.076. The possible relationship of this anion to the old and still unsolved problem of what complex or complexes are present in solutions of “ruthenium blue” is considered. The existence of bonding interactions between adjacent metal atoms is proposed and discussed.