Edge-sharing bi-octahedral diruthenium(iv,iv) compounds containing Ru–Ru bonds chelated and bridged by two carbonate and two oxo groups

Abstract

From paddle–wheel starting material Na₃Ru₂(CO₃)₄·6H₂O, a family of edge-sharing bi-octahedral (ESBO) diruthenium(IV,IV) compounds formulated as Ru₂O₂(CO₃)₂(H₂O)₂L₂·nH₂O [L = piperazine (1) or 2-methylpiperazine (2), n = 4, and L = 2,2-dimethylpiperazine (3), n = 12] and Ru₂O₂(CO₃)₂(OH)₄{M(H₂O)₄}₂·nH₂O [M = Mg (4), n = 4, and Ni (5), n = 2] were prepared and structurally characterized. The Ru₂⁸⁺ dimer is chelated and bridged by two CO₃²⁻ and two μ-O in a trans manner, and the Ru–Ru distances fall in the range 2.3808(6)–2.4001(4) Å. Compound 2 shows the shortest Ru–Ru distance for all known ESBO Ru₂ compounds reported thus far. Increasing –CH₃ groups of terminal piperazine ligands coordinated to the Ru(μ-O)₂(μ-O₃C)₂Ru core, and according to Raman spectra experiments combined with theoretical calculations, the intense bands of compounds 1–3 appearing at ∼360 cm⁻¹ can be assigned to the stretching of Ru–Ru bonds.