The single crystalEPR results of [NiBr2(diars)2]Br, a low spin Ni(III) complex, magnetically diluted in [Co(NO)Br(diars)2]Br show a very large bromine hyperfine coupling. The experimental g, ligand hyperfine splitting due to arsenic and bromine and spin densities are compared with other analogous diphos and diars complexes. The unpaired electron is essentially in the$$d_{z^2 } $$ orbital and there is extensive delocalization over all the ligand nuclei due to extended 4s and 4p radial wave functions. On the other hand the pure crystal of [NiBr2(diars)2]Br shows single exchange averagedEPR line. Linewidth analysis using the existing theories of exchange gives values of roughly 800 G and 380 G for respectively isotropic and intersite exchange interactions in this system.
