Magnetic and high-frequency EPR studies of an octahedral Fe(iii) compound with unusual zero-field splitting parameters

Abstract

Temperature-dependent magnetic susceptibility and multi-frequency EPR (9.4, 34.5, 94 and 188 GHz) spectroscopic measurements have been carried out together with an X-ray study at 100 K to study [Fe(DMSO)(6)](NO(3))(3). The iron(III) ion remains high-spin (S = 5/2) in the temperature range studied, therefore, the EPR data were interpreted using the conventional S = 5/2 spin Hamiltonian. A full analysis of EPR spectra at 95 GHz of a powdered sample at 290 K revealed that they are extremely sensitive to D and E values. The zfs parameters were precisely determined: D = + 0.1730 cm(-1), E = 0.00 cm(-1) and lambda = |E/D| = 0.00. A sequence of the spectra neatly shows that the compound has a clear magnetic dependence on temperature. The study at 5 K, showed that the zfs parameters increase: D = + 0.1970 cm(-1), E = 0.017 cm(-1) and lambda = |E/D| = 0.086. These data indicate that as the temperature decreases the D tensor increases slightly showing an increase in the rhombicity. These results confirm that |2D| is congruent to h nu at X-band in this case. Additionally, it has been shown by X-ray crystal analysis of [Fe(DMSO)(6)](NO(3))(3) at 100 K that this is involved in a hydrogen bonding network, consisting of C-H...O interactions between the nitrate anions and the methyl groups of the coordinated DMSO molecules, thus suggesting that the differences found in the spectroscopic parameters D and E at different temperatures must be due to these supramolecular interactions.

Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate

“…Typically, Fe 3+ , Ni 2+ , and Ni 0 have associated EPR signals, while Fe 2+ , Fe 0 , and Ni 3+ do not. [ 39–41 ] As displayed in Figure 2e, no obvious resonance signal was detected from NiSe 2 (black line). On the other hand, broad EPR signals were obtained for all the samples containing Fe, with the highest signal intensity being observed for the sample containing the lowest amount of Fe, Ni 0.75 Fe 0.25 Se 2 .…”

Copper thiocyanato complexes and cocaine – a case of ‘black cocaine’

“…E.g. for solid (NMe 4 ) 3 [Fe(NCS) 6 ] EPR spectroscopy and Mössbauer indicate high spin ( S = 5/2) behaviour, and [Fe(DMSO) 6 ] 3+ gave an EPR signal indicative for an S = 5/2 ground state also at 298 K . However, for [Fe(4,4’‐bpy) 2 (NCS) 3 ] × acetone containing five‐coordinate Fe 3+ , EPR signals were only recordable below 100 K, probably due to its intermediate spin system ( S = 3/2), and an early report by Golding and Orgel on the EPR signal of Fe(NCS) 3 in acetone has never been confirmed .…”

“…E.g. for solid (NMe 4 ) 3 [Fe(NCS) 6 ] EPR spectroscopy and Mössbauer indicate high spin (S = 5/2) behaviour, [64] and [Fe(DMSO) 6 ] 3+ gave an EPR signal indicative for an S = 5/2 ground state also at 298 K. [65] However, for [Fe(4,4'-bpy) 2 (NCS) 3 ] × acetone containing five-coordinate Fe 3+ , EPR signals were only recordable below 100 K, probably due to its intermediate spin system (S = 3/2), [66] and an early report by Golding and Orgel on the EPR signal of Fe(NCS) 3 in acetone has never been confirmed. [67] Our attempts to obtain EPR spectra in glassy frozen acetone solution of samples #4 and #5 were unsuccessful and we assume that the proposed species [Fe(NCS) x ] nÀ (x = 4-6; n = 1-3) in these solutions (and in the acetone extract) were EPR silent under these conditions due to unfavourable relaxation.…”

Zero-Field Splitting Parameters of Hemin Investigated by High-Frequency and High-Pressure Electron Paramagnetic Resonance Spectroscopy

“…The results could explain the trend in D values, but the calculated D values were smaller than the experimentally determined D values by several factors. It is noted that highspin ferric complexes such as [Fe(TPP)]X exhibit unusually large D values, on the order of 1-10 cm −1 [51,52]), compared to other transition metal complexes (usually ∼0.1 cm −1 ) [53]), thus making quantitative calculation very difficult. Moreover, the rhombic component E of metalloporphyrin is much smaller than D in many cases, and greater accuracy is required in the calculation.…”