The addition of methyl iodide to the heterotrinuclear compound [{Rh(mu-pz)(mu-S-t-Bu)(CO)(P(OMe)(3))}Pd-2] leads to the formation of the complex [{Rh(mu-pz)(mu-S(t)Bu)I-(Me)(CO)(P(OMe)(3))}Pd-2] . After 36 h of reaction the spectroscopic data indicate the only presence of the acetyl derivative [{Rh(mu-pz)(mu-S(t)Bu)I(COMe)(P(OMe)(3))}Pd-2] whose structure has been determinated by X-ray diffraction study. The present paper reports a methylation process which deals with a MeOC-Rhm(III)... Pd ... Rh-III-COMe system. [GRAPHICS] t> Rh-III-COMe system. [GRAPHICS] ation of a dimeric entity is achieved by a bridging ClO4 while hydrogen bonds from the imino groups to terminal and bridging ClO4 link two dimers to yield a "dimer of dimers". [GRAPHICS] GRAPHICS]