Unstable intermediates. Part 114.—Solid-state electron spin resonance study of pentacyanocobalt phenyl nitroxide

Abstract

A combination of solid-state e.s.r. studies and line-width analysis has yielded the following parameters for the nitroxide formed by reaction of nitrobenzene with pentacyanocobaltate(II) ions: for ¹⁴N; A_x= 32 G, A_y=A_z= 5 G; for ⁵⁹Co; A_x=A_y= 8.5 G, A_z= 15.0 G, and g_x= 2.000, g_y= 2.008, g_z= 2.012. For the 2,4,6-trichloro-derivative, we find for ¹⁴N; A_x= 40 G, A_y=A_z= 5.5 G; for ⁵⁹Co; A_x=A_z= 10 G, A_y= 18 G and g_x= 1.999, g_y= 2.007, g_z= 2.012. These results confirm the conclusion of Swanwick and Waters that these radicals are effectively nitroxides, with the unpaired electron largely confined to a π orbital comparable with that for the corresponding alkyl phenyl nitroxides. Delocalization onto cobalt by pπ—dπ bonding, although possible, is slight, and the cobalt hyperfine coupling can be entirely accommodated in terms of spin polarization of the nitrogen-cobalt σ-bonding electrons.