Synthesis, photophysical and redox behavior of unsymmetrical binuclear Ru(II) complexes based on tris(1-pyrazolyl)methane

Six new unsymmetrical achiral complexes of RuII containing the tripodal ligand tris(1-pyrazolyl)methan (tpm) on both metal centers have been prepared and fully characterized. Their general formula is [CLa(tpm)Ru(μBL)Ru(tpm)CLb]4+, were CLa and CLb represent two different chelating ligands (2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) or 2,2′-biquinoline (biq)); BL can be 4,4′-bipyridine (4,4′-bpy) or pirazine (pz). The structures of the new species have been elucidated by 1H NMR, COSY and NOESY spectroscopy. Electrochemical, UV–Vis spectroscopical, luminescence, and spectroelectrochemical properties have been investigated for all the binuclear complexes. For two representative species DFT calculations were carried out. The experimental data have been thoroughly interpreted in terms of the role played by each constituent subunit within the assemblies.These results add comparative pieces of information to the knowledge of the properties of the RuII-based complexes.

Electrochemical, photophysical, and spectroelectrochemical behaviors point out that the presence of different chelating ligands within the coordination sphere of each RuII atom finely tunes the electronic properties of six novel binuclear complexes.The achirality of the new species allows a complete analysis of their interesting 1H NMR features.Figure optionsDownload as PowerPoint slideHighlights
► A new family of six unsymmetrical achiral binuclear Ru(II) complexes were synthesized and fully characterized.
► Their photophysical and redox properties have been investigated.
► The experimental results, supported also by DFT calculations carried out for two representative species, show that by suitable choice and combination of the building blocks, a fine tuning of the electronic properties of the binuclear architectures is possible.
► This study adds comparative pieces of information to the knowledge of the properties of the RuII-based subunits.