Synthesis, spectroscopy, tandem mass spectrometry, and electrochemistry of the linearly bridged μ-{ trans-1,4-bis[2-(4-pyridyl)ethenyl]-benzene}-{Ru 3O(CH 3COO) 6(py) 2} 2 cluster

Abstract

The novel polynuclear [{Ru 3O(CH 3COO) 6(py) 2} 2(BPEB)](PF 6) 2 species containing the linear bridging trans-1,4-bis[2-(4-pyridyl)ethenyl]-benzene ligand (BPEB) was synthesized and its structural characterization carried out by means of positive ion electrospray (ESI-MS) and tandem mass (ESI-MS/MS) spectrometry, as well as by 1H NMR spectroscopy. The doubly charged cation [{Ru 3O(CH 3COO) 6(py) 2} 2(BPEB)] 2+ was detected in the ESI-MS mass spectrum as a multiple-component isotopomeric ionic cluster centered at m/ z 974, which ion abundance and m/ z distribution matched perfectly the isotopic pattern calculated for this multiple isotope Ru 3-containing ion. The tandem mass spectrum of [{Ru 3O(CH 3COO) 6(py) 2} 2(BPEB)] 2+ provided a structural diagnostic dissociation behavior, on the basis of the characteristic charge splitting and sequential ligand loss steps. The cyclic voltammograms of the complex exhibited a quasi-reversible multistep redox behavior, displaying three waves at 1.14, 0.08, and −1.21 V ascribed to the [Ru 3O] 2+/1+/0/1− processes and two waves at −1.56 and −1.78 V ascribed to the BPEB 0/1−/2− redox processes which are also observed in the free ligand, at −1.48 and 1.61 V, respectively. In spite of the conducting nature of the bridging ligand, the electrochemical and spectroelectrochemical results indicated a weak electronic coupling between the triangular cluster centers.