Paramagnetic transition-metal carbonyls and cyanides. Part II. An electron spin resonance study of the radiolysis of thallium(I) tetracarbonylcobaltate

Abstract

Exposure of thallium(I) tetracarbonylcobaltate to ⁶⁰Co γ-rays at 77 K gives a high-field resonance identified as a thallium(II) centre, together with an isotropic eight-line centre having A≈ 500 G and g= 1.96. This unusually large hyperfine coupling to ⁵⁹ Co corresponds to ca. 38% spin density in the outer, 4s, orbital, and the low g value implies some 4p character. It is suggested that this is due to the [Co(CO)₄]^2– anion which is probably distorted from the original tetrahedral structure. A third species, having A₁₈₀(⁵⁹Co)= 25 G and g_av.= 1.998 is tentatively identified as [Co(CO)₄]^2– with the unpaired electron confined to one CO ligand. At room temperature the only e.s.r. signal detected corresponds to a species having the properties expected for the peroxide [Co(CO)₄(O₂)].