Abstract
The mono‐ and binuclear organometallic Ni^II^ complexes [(μ‐bpym){Ni(Mes)Br}~n~] (bpym = 2,2′‐bipyrimidine; n = 1 or 2; Mes = mesityl = 2,4,6‐trimethylphenyl) were prepared and characterised electrochemically and spectroscopically (NMR, UV/Vis/NIR) in detail. The long‐wavelength absorptions for the binuclear complex reveal a marked electronic coupling of the two metal centres over the ligand bridge via their low‐lying π*‐orbitals. While the mononuclear complex undergoes rapid dissociation of the bromido ligand after one‐electron reduction the binuclear derivative exhibits reversible reductive electrochemistry and both of them yield stable radical anionic complexes with mainly bpym ligand centred spin density as shown by EPR spectroscopy of the free ligand bpym and the nickel complexes. The molecular structure of the binuclear bpym complex [(μ‐bpym){Ni(Mes)Br}~2~] was studied by EXAFS in comparison to the mononuclear analogue [(bpym)Ni(Mes)Br] revealing markedly increased Ni–C/N distance of the first coordination shell for the binuclear derivative suggesting an optimum overlap for the mononuclear complex, while two nickel complex fragments {Ni(Mes)Br} are seemingly too large to fit into the bis‐chelate coordination site.