Structure and reactivity of transition-metal complexes with polyatomic ligands. Part IV. Electron spin resonance spectra of γ-irradiated sodium nitroprusside

Abstract

Electron spin resonance spectra have been recorded for γ-irradiated hydrated and anhydrous sodium nitroprusside. The paramagnetic species in the anhydrous salt, and in polarographically reduced sodium nitroprusside in dimethylformamide is identified as the ion [Fe(CN)₅NO]^3– having linear Fe–N–O bonds, whereas the species in the hydrated salt is possibly [Fe(CN)₄(CNOH)(NO)]^2– having an Fe–N–O bond angle of about 170°. The directions and the magnitudes of the g and ¹⁴N hyperfine tensors are in accord with an electron configuration e⁴, b₂², a₁¹, the a₁ orbital being primarily d_z². Some radicals were trapped in pairs giving a weakly interacting triplet state. Single-crystal measurements of the spectra from such pairs showed that the unpaired electron was localised mainly on the iron nucleus. None of these results is compatible with the configuration 1e⁴, b₂², 2e¹ in which the 2e orbital is largely π*(NO).