A complete series of tricarbonylhalidorhenium(I) complexes (abpy)Re(CO)3(Hal), Hal = F, Cl, Br, I; abpy = 2,2′-azobispyridine: Structures, spectroelectrochemistry and EPR of reduced forms

For the first time a complete set of tricarbonylhalidorhenium(I) complexes (Hal = F, Cl, Br, I) has been studied in a systematical fashion by example of (abpy)Re(CO)₃(Hal), abpy = 2,2′-azobispyridine. Crystal structures of chloride, bromide and iodide analogues are now available, showing increasing planarization of the abpy ligand in that order. Cyclic voltammetry, EPR, IR and UV/Vis spectroelectrochemistry of the reduced forms (abpy)Re(CO)₃(Hal)]⁻ illustrate that the four halide complexes differ only partially in their properties. The strongest deviations are observed for (abpy)Re(CO)₃F]⁻ which is distinguished by the widest electrochemical potential range but most pronounced chemical lability. In the EPR spectrum the fluoride exhibits the highest isotropic g value (2.0085) and the lowest rhenium coupling constant, which is of the same magnitude (2 mT) as the detectable ¹⁹F hyperfine splitting.