Spectroscopic and Structural Study of Metal−Metal Bonded Metalloporphyrinic Derivatives:  the Case of Rhodium−Indium

The synthesis and spectroscopic characterization of heterometallic porphyrinate derivatives containing rhodium−indium metal−metal bonds are reported. The investigated compounds are represented by the formula [(Porph)RhIn(Porph‘)], where Porph and Porph‘ are OEP, TPP, β-Cl4TPP, β-Cl8TPP, or TPyP. UV−Visible spectroscopy of the title complexes confirms the presence of a strong π−π interaction between the macrocycles in each derivative and denotes the effect of the nontransition metal in their optical features. For comparison purposes, a new bimetallic complex with a rhodium−thallium metal−metal bond is also presented. According to 1H and 13C NMR data, we were able to distinguish two major NMR regions: the endo- between the metal−metal bonded macrocycles and the exo-, which are characteristic features of porphyrinic complexes at very close proximity. X-ray absorption spectroscopy (XAS) structural characterization of Rh−In bond was performed on the [(OEP)RhIn(OEP)] complex, in the fluorescence mode, and we essentially focused on the metal−metal distance determination. Finally, the distance of 2.543(3) Å was deduced from the X-ray structure of a new [(TPP)RhIn(TPyP)] derivative.