Resonance Raman and X-ray Crystallographic Studies of Intertriad Metal-Metal Bonds. 2. WRu and MoOs Porphyrin Dimers

Electrochemical and resonance Raman studies of nitridomanganese(V) porphyrins in nonaqueous solution

The UV-vis spectral, electrochemical and resonance Raman data of [meso-tetrakis(4-pyridyl)porphyrinato]nitridomanganese(V), MnN(TPyP) , were investigated. MnN(TTP) (where ( TTP )2− = dianion of meso-tetrakis(p-tolyl)porphyrin) and MnN(OEP) (where ( OEP )2− = dianion of 2,3,7,8,12,13,17,18-octaethylporphyrin) were also examined in comparison. Cyclic voltammetry of MnN ( TPyP ) showed an irreversible oxidation wave at +1.22 V and two redox couples at −1.05 and −1.40 V vs. Ag / AgCl , respectively. According to spectroelectrochemical studies, the first and the second reductions involved formation of the porphyrin anion and dianion, respectively, the latter leading to a phlorin. The electron-withdrawing 4-pyridyl substituent shifted the redox potential of the porphyrin ring to a more positive value. However, the bond strength of the Mn - N triple bond was not affected. Resonance Raman studies indicated that the Mn≡N stretching frequencies (νMnN) occurring within 1050 ± 1 cm−1 in various solvents did not change significantly. The hydrogen-bonding between methanol and MnN ( TPyP ) lowered νMnN to 1040 cm−1. A further lowering of νMnN was found in the presence of nitrogeneous bases such as imidazole (ImH), piperidine (Pip) and pyridine (Py) and may be due to coordination to the manganese center. νMnN is correlated with the pKa's of a series of pyridines.

Structural and Spectroscopic Characterization of a Diruthenium o-Dioxolene Complex Possessing a Singly Occupied Molecular Orbital Delocalized over the Entire Molecule, [Ru2(3,6-DTBDiox)4]-

Chemical oxidation of [Ru2(6+)(3,6-DTBCat)4]2- affords [n-Bu4N][Ru2(3,6-DTBDiox)4].acetone (2.acetone). The oxidized species was characterized by X-ray crystallographic analysis and EPR, and the delocalization of the unpaired electron over the entire molecule was indicated. This example showed that the utilization of redox-active ligands into a Ru2 complex expanded the degree of freedom in the electronic structure. DFT calculations support this view, and the spin population was estimated to be approximately 18% and 82% for the Ru2 core and the four dioxolene ligands, respectively.

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, beta-Cl(4)TPP, beta-Cl(8)TPP, or TPyP. UV-Visible spectroscopy of the title complexes confirms the presence of a strong pi-pi 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 (1)H and (13)C 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) A was deduced from the X-ray structure of a new [(TPP)RhIn(TPyP)] derivative.