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A new octanuclear mixed-valence cobalt acetate complex of the cationic type [Co4IICo4III(μ4-O)4(μ3-OMe)4(μ-OAc)6(H2O)8]F2 · 10H2O ([I]F2 · 10H2O) was prepared by crystallization from a solution of ‘cobalt(III) acetate’ in a Me2CO-MeOH-H2O-HF mixture and studied by X-ray diffraction. The crystals are monoclinic: space group C2/c, a = 17.222 A, b = 16.836 A, c = 16.586 A, β = 94.902°, Z = 4, R = 4.37% (I > 2σ(I)). In the crystal, the I2+ complex cations, fluoride anions, and solvate water molecules form a three-dimensional (3D) coordination supermolecular system.

The reaction of [Ru 3 III (μ3-O)(μ-O2CCF3)6(H2O)3](O2CCF3) in methanol gives two solvates, [Ru3O(O2CCF3)6(DMSO)3] · 1/2H2O (I) and [Ru3O(O2CCF3)6(DMSO)3] · H2O (II), of a novel trinuclear mixedvalence Ru(II,III,III) trifluoroacetate complex, where two DMSO molecules are coordinated to the Ru atoms through the O atom, while the third DMSO molecule is coordinated through the S atom. According to the X-ray diffraction data, the complex can crystallize in two crystal systems: triclinic (I) (space group P $$\overline 1 $$ ) and monoclinic (II) (space group P21/m). The unit cell parameters for I are: a = 9.354, b = 11.005, c = 20.846 A, α = 99.10, β = 96.38, γ = 92.17, Z = 2; R = 7.27%; for I are: a = 9.186, b = 17.044, c = 13.091 A, β = 101.10, Z = 2; R = 14.18%.

Binuclear ruthenium μ-oxocarboxylates of the nonelectrolyte type [Ru2III(μ-O)(μ-O2CR)2Py4(O2CR)2] (R = C(CH3)3, CH3, Ph, CH2Cl, CCl3, and CF3) were obtained and studied by electronic absorption and IR spectroscopy and FAB mass spectrometry. The carboxylate ions RCO2− are symmetrically arranged (trans with respect to the bridging μ-O atom) and coordinated in a monodentate fashion. According to X-ray diffraction data, the crystals of [Ru2III(μ-O)(μ-O2CCF3)2Py4(O2CCF3)2] ⋅ (CH3)2CO are monoclinic; the unit cell parameters are a = 11.705(2) A, b = 16.166(3) A, c = 20.917(4) A, β = 103.47(3)°, space group C2/c, Z = 4. The RCO2− groups that are trans to the μ-O atom can be easily replaced by pyridine or acetonitrile.

The reactions between trans-[OsVIO2Cl2L2] (L = PPh3, AsPh3, SbPh3) and carboxylic acids RCO2H (R = CH3, C(CH3)3, CH2Cl, CCl3, CF3) are studied. The resulting binuclear compounds were found to have the general formula [Os2IV(μ-O)(μ-O2CR)2Cl4(L)2] (L = PPh3; R = CH3, C(CH3)3, CH2Cl, CCl3, CF3, and L = AsPh3; R = CH3, CH2Cl, CCl3, CF3). X-ray diffraction analysis revealed that the [Os2IV(μ-O)(μ-O2CCCl3)2Cl4(PPh3)2] · CH2Cl2 complex crystallizes in a triclinic system with space group P\(\bar 1\); a = 10.747(2) A, b = 19.291(4) A, c = 24.614(5) A, α = 100.08(3)°, β = 90.63(3)°, γ = 97.05(3)°, V = 4983.5(17) A3, Z = 4. The Os(μ-O)Os angle is 142.2(7)°. The interaction of trans-[OsVIO2Cl2(SbPh3)2] with all the acids under study is attended by intramolecular redox reaction resulting in SbCl2Ph3.

Cyclic voltammetry and galvanostatic coulometry techniques were used to determine how the redox properties of osmium binuclear μ-oxocarboxylates [Os2 IV(μ-O)(μ-O2CR)2Cl4L2] (R = CH3, CCl3; L = PPh3 and R = CH3; L = AsPh3) are influenced by the nature of the bridging carboxylate ligand RCOO– and ligand L. It was shown that all compounds in solution of dichloromethane undergo two single-electron reduction processes. The data obtained were compared with the DFT calculations of the electronic structure of the model complexes [Os2 IV(μ-O)(μ-O2CR)2Cl4L′2] (R = CH3, CCl3; L′ = PH3 and R = CH3; L′ = AsH3).

The current state of investigations of homonuclear cobalt(III), rhodium(III), and iridium(III) complexes containing bridging O atoms and bridging carboxylato groups is reviewed.