Coordinating Tectons. Experimental and Computational Infrared Data as Tools To Identify Conformational Isomers and Explore Electronic Structures of 4-Ethynyl-2,2′-bipyridine Complexes

4-Ethynyl-2,2′-bipyridyl-substituted ruthenium alkynyl complexes have been prepared and used to access a range of binuclear homometallic ruthenium and heterometallic 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 ruthenium complexes undergo reversible one-electron oxidations centered largely on the alkynyl ligands, as inferred from the significant shift in ν(C≡C) frequency on oxidation, while the binuclear complex [RuC≡C-4-bpy-κ2-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 [RuC≡C-4-bpy-κ2-N,N′-RuClCp(dppe)Cp*]+ as a weakly coupled class II mixed-valence compound (Hab = 306 cm–1). These results indicate that there is improved electronic communication through the 4-ethynyl-2,2′-bipyridyl ligand in comparison to the analogous 5-ethynyl-2,2′-bipyridyl complexes (Hab = 17 cm–1).