The synthesis and spectroscopic characterization of four heterometallic porphyrinate dimers containing rhodium-thallium metal-metal bonds are reported. The investigated compounds are represented by the formula (Porph)-Rh-Tl(Porph'), where Porph and Porph' are OEP and/or TPP. UV/visible :spectroscopy of the title complexes confirms the presence of a strong pi-pi interaction between the macrocycles in each derivative. With H-1 and C-13 NMR data, we were able to distinguish two major NMR regions : the endo, between the metal-metal bonded macrocycles, and the exo, outside the macrocycles, which are characteristic features of porphyrinic dimers. Tl-205 NMR for the title complexes was performed, and the chemical shifts of the thallium nucleus are presented. For the four complexes, the magnitudes of spin-spin coupling constants between thallium and rhodium nuclei have been measured for the first time. Finally, reactions with selected substrates were studied in order to investigate the reactivity as well as the polarity of the metal-metal bond.