Coordination of weakly binding anions to [Ru₂(μ-O ₂CCH₃)₄]⁺ in aqueous solution

Four new complexes involving the diruthenium(II,III) tetraacetate core, [Ru₂(μ-O₂CCH₃)₄]⁺, with three relatively weakly binding anions ClO4-, NO3- and CF₃CO2- have been synthesized and structurally characterized in exclusively aqueous media. Despite their low, but still positive, apparent donor numbers (D.N.) in water (according to previous literature by Linert et al.) both NO3- (D.N. = 0.21) and CF₃CO2- (D.N. < 8.65) do coordinate axially to [Ru ₂(μ-O₂CCH₃)₄]⁺, with water having a D.N. = 19.5. NO3- forms both a polymer, [Ru₂(μ- O₂CCH₃)₄(NO₃)]_x, and a mixed axial adduct with water, [Ru₂(μ-O₂CCH ₃)₄(H₂O)(NO₃)] depending on reaction stoichiometry. CF₃CO2- forms a double salt of the form [Ru ₂(μ-O₂CCH₃)₄(H₂O) ₂] [Ru₂(μ-O₂CCH₃) ₄(CF₃COO)₂]â̄2H₂O. ClO4-, with a negative apparent D.N. in water of -12.4, only "binds" outer-sphere to form [Ru₂(μ-O₂CCH₃) ₄(H₂O)₂](ClO₄), at all reaction stoichiometries (as does the PF6- ion whose structure was also determined and found to be the same as a previous result). These results are compared to the very limited data of [Ru₂(μ-O₂CCH₃) ₄]⁺ adduct salts in aqueous solution and it is concluded that despite the low donor numbers, as long as they are positive, the species formed in water can be every bit as varied and rich as those formed in other solvents.