The 'H NMR spectra of acetate methyl signals of the titled three complexes in CD,OD change with time due to successive substitution of CD,OD for the coordinated water molecules. The first-order rate constants for the first methanol-d., substitution of the triruthenium(II1) and trirhodium(II1) complexes are 7.7~10~~ s-' (298.2 K)(~S=103f6kTmol~'andAS*=+41+12JK~'mol~'at0-21"C)and1.3~10~3s~'(298.2K)(~*=102f9 kJ mol-' and AS*= +42+32 J K-i mol-' at O-10 "C) per one metal ion, respectively, which are greater by approximately 2 and 6 orders of magnitude, respectively, than the water exchange reactions of the hexaaqua complexes of 'these metal ions. The trans effect of the central oxide ion is considered as a major factor responsible for the labrlization. The first-order rate constants for the mixed-metal rhodium-diruthenium complex at 298.2 K are 9.9~10~~ (M*=109f4 kJ mol-' and AS*= +44+9 J K-' mol-r) and 7.9X10m5 s-r (tiS=103f3 kJ mol-' and AS*= +22*6 J K-i mol-' at 10.1-35.3 "C) at ruthenium and rhodium centers, respectively, which are c. 10 times smaller than the corresponding values for the homonuclear complexes. The slower rates in the muted-metal complex indicate that electronic configuration in the molecular orbital based on (metal-d?r)-(oxygen-pr) interactions plays some role in controlling the substitution rate. On the basis of the activation parameters, a dissociative mechanism is proposed for all these reactions. 'Ir(II1) is probably the most inert trivalent metal ion so far studred [ll].