4-Ethynyl-2,2'-bipyridyl substituted ruthenium alkynyl complexes have been prepared and used to access a range of binuclear homo-metallic ruthenium and hetero-metallic ruthenium-rhenium complexes. These have been characterized by a variety of spectroscopic and single-crystal X-ray diffraction experiments. The IR spectra of a number of these ruthenium alkynyls display multiple ν(C≡C) bands in the IR spectra, which are rationalized in terms of putative conformational isomers, whose calculated infrared stretching frequencies are comparable to those obtained experimentally. The mononuclear alkynyl complexes Ru(C≡C) undergo reversible one electron oxidations centered largely on the alkynyl ligands as inferred from the significant shift in ν(C≡C) frequency on oxidation, whilst the binuclear complex [Ru{C≡C-4bpy-κ 2-N,N'-RuClCp}(dppe)Cp*] + undergoes initial oxidation at the very electron rich {RuCl(bpy)Cp} fragment causing only a small change in ν(C≡C). A combination of IR and UV-vis spectroelectrochemical experiments, supported by quantum chemical calculations on a selected range of conformers, led to the classification of [Ru{C≡C-4-bpy-κ 2-N,N'-RuClCp}(dppe)Cp*] + as a weakly Class II mixed valence compound (H ab = 306 cm-1). These results indicate that there is improved electronic communication through the 4-ethynyl-2,2'-bipyridyl ligand compared to the analogous 5-ethynyl-2,2'-bipyridyl complexes (H ab = 17 cm-1).
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