Further e.s.r. studies of γ-irradiated hydrated sodium nitroprusside

Abstract

Four paramagnetic centres have been detected and characterised by e.s.r. in hydrated sodium nitroprusside after exposure to γ-rays at 77 K. One, shown to be nitric oxide, only gave a detectable signal at 19 K. Two others, very closely related, where similar to the nitric oxide centre except that A_iso was ca. 17 G rather than ca. 6 G. These centres are thought to be [Fe^II(CN)₅NO]^3– ions with the unpaired electron in a pseudo-π-orbital, largely centred on the NO ligand. The fourth centre, stable at room temperature, is a normal low-spin d⁷ iron complex, previously identified as [Fe^I(CN)₅NO]^3–. Careful examination of the low temperature e.s.r. Spectra of this species has revealed possible shoulders indicative of interaction with a nucleus with I= 1 and having A=ca 2–3 G. By analogy with the behaviour of various hexacyanides, we tentatively suggest that the trans-cyanide has become an isocyanide.