Single crystal EPR studies of [enH(2)][{Fe(HEDTA)}(2)O]center dot 6H(2)O [en = ethylenediamine; HEDTA = N-hydroxyethylethylenediaminetriacetate(3-)]

Single-crystal EPR studies of the Fe-O-Fe dimer, [enH(2)] [{Fe(HEDTA)}(2)O] . 6H(2)O, have been performed at both X- and Q-band frequencies and room te mperature. Resonances arising from the S' = 1, 2, and 3 states have been ob served in the powder spectrum at Q-band frequency and analysis by spectral simulation has led to the zero-field splitting parameters: \D-1\ = 1.950 cm (-1), \E-1\ = 0.650 cm(-1), \D-2\ = 0.150 cm(-1), \E-2\ = 0.0195 cm(-1), \D -3\ = 0.570 cm(-1), and \E-3\ = 0.000 cm(-1). In addition, analysis of thre e orthogonal planes of single-crystal EPR data at both X- and Q-band freque ncies has allowed the orientation of the zero-field splitting tensor with r espect to the molecular geometry in the dominant (S' = 2) state to be deter mined. The largest principal value of the D tensor (D-zz) is found to lie a pproximately perpendicular to the plane of the Fe-O-Fe bridge; the nonlinea r bridging angle is 165 degrees. The results obtained in this study are com pared with those from a number of other studies. A pattern for the orientat ions of the zero-field splitting parameters in the dominant spin state (S' = 2) of the Fe-O-Fe dimers, so far studied by single-crystal EPR spectrosco py, emerges.