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High‐frequency/high‐field EPR spectroscopy of the high‐spin ferrous ion in hexaaqua complexes
Author(s) -
Telser Joshua,
van Slageren Joris,
Vongtragool Suriyakan,
Dressel Martin,
Reiff William M.,
Zvyagin S. A.,
Ozarowski Andrew,
Krzystek J.
Publication year - 2005
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1689
Subject(s) - electron paramagnetic resonance , chemistry , perchlorate , spectroscopy , ferrous , magnetic field , ion , analytical chemistry (journal) , crystallography , nuclear magnetic resonance , condensed matter physics , physics , organic chemistry , quantum mechanics , chromatography
Electron paramagnetic resonance (EPR) at conventional magnetic fields and microwave frequencies, respectively, B 0 ≤ 1.5 T, ν ≤ 35 GHz, has been widely applied to odd electron‐number ( S = 1/2) transition metal complexes. This technique is less successfully applied to high‐spin systems that have even electron configurations, e.g. Fe 2+ ( S = 2). The recently developed technique of high‐frequency and high‐field EPR (HFEPR), employing swept fields up to 25 T combined with multiple, sub‐THz frequencies readily allows observation of EPR transitions in such high‐spin systems. A parallel spectroscopic technique is frequency‐domain magnetic resonance spectroscopy (FDMRS), in which the frequency is swept while at zero, or at discrete applied magnetic fields. We describe here the application of HFEPR and FDMRS to two simple high‐spin (HS) ferrous (Fe 2+ ) salts: ferrous perchlorate hydrate, [Fe(H 2 O) 6 ](ClO 4 ) 2 and (NH 4 ) 2 [Fe(H 2 O) 6 ](SO 4 ) 2 , historically known as ferrous ammonium sulfate . Both compounds contain hexaaquairon(II). The resulting spectra were analyzed using a spin Hamiltonian for S = 2 to yield highly accurate spin‐Hamiltonian parameters. The complexes were also studied by powder DC magnetic susceptibility and zero‐field Mössbauer effect spectroscopy for corroboration of magnetic resonance results. In the case of [Fe(H 2 O) 6 ](ClO 4 ) 2 , all the magnetic techniques were in excellent agreement and gave as consensus values: D = 11.2(2) cm −1 , E = 0.70(1) cm −1 . For (NH 4 ) 2 [Fe(H 2 O) 6 ](SO 4 ) 2 , FDMRS and HFEPR gave D = 14.94(2) cm −1 , E = 3.778(2) cm −1 . We conclude that the spin‐Hamiltonian parameters for the perchlorate best represent those for the isolated hexaaquairon(II) complex. To have established electronic parameters for the fundamentally important [Fe(H 2 O) 6 ] 2+ ion will be of use for future studies on biologically relevant systems containing high‐spin Fe 2+ . Copyright © 2005 John Wiley & Sons, Ltd.