X-ray and Nuclear Spectroscopies to Reveal the Element-Specific Oxidation States and Electronic Spin States for Nanoparticulated Manganese Cyanidoferrates and Analogs

In this publication, the potential non-gadolinium magnetic resonant imaging agent—nanoparticulate K2Mn[Fe(CN)6]—its comparison sample KFe[Co(CN)6], as well as their reference samples were measured and analyzed using Mn, Co and Fe L-edge X-ray absorption spectroscopy (L XAS). From the information obtained, we conclude that K2Mn[Fe (CN)6] has a high spin (hs)-Mn(II) and a low spin (ls)-Fe(II), while KFe[Co(CN)6] has an hs-Fe(II) and an ls-Co(III). In these Prussian blue (PB) analog structures, the L XAS analysis also led to the conclusion that the hs-Mn(II) in K2Mn[Fe(CN)6] or the hs-Fe(II) in KFe[Co(CN)6] bonds to the N in the [M(CN)6]4−/3− ions (where M = Fe(II) or Co(III)), while the ls-Fe(II) in K2Mn[Fe(CN)6] or the ls-Co(III) in KFe[Co(CN)6] bonds to the C in the [M(CN)6]4−/3− ion, suggesting the complexed metalloligand [Mn(II) or Fe(II)] occupies the N-bound site in PB. Then, nuclear resonant vibrational spectroscopy (NRVS) was used to confirm the results from the L XAS measurements: the Mn(II), Eu(III), Gd(III), Fe(II) cations complexed by [M(CN)6]n−-metalloligand all take the N-bound site in PB-like structures. Our NRVS studies also prove that iron in the K2Mn[Fe(CN)6] compound has a 2+ oxidation state and is surrounded by the C donor atoms in the [M(CN)6]n− ions.