Structure, Electrochemistry, and Magnetism of the Iron(III)-Substituted
Keggin Dimer, [Fe<sub>6</sub>(OH)<sub>3</sub>(<i>A-</i>α<i>-</i>GeW<sub>9</sub>O<sub>34</sub>(OH)<sub>3</sub>)<sub>2</sub>]<sup>11-</sup>
Li-Hua Bi
Ulrich Kortz
Saritha Nellutla
Ashley C. Stowe
Johan van Tol
Naresh S. Dalal
Bineta Keita
Louis Nadjo
10.1021/ic048713w.s001
https://acs.figshare.com/articles/dataset/Structure_Electrochemistry_and_Magnetism_of_the_Iron_III_Substituted_Keggin_Dimer_Fe_sub_6_sub_OH_sub_3_sub_i_A_i_i_i_GeW_sub_9_sub_O_sub_34_sub_OH_sub_3_sub_sub_2_sub_sup_11_sup_/3300130
The iron(III)-substituted tungstogermanate [Fe<sub>6</sub>(OH)<sub>3</sub>(<i>A</i><i>-</i>α<i>-</i>GeW<sub>9</sub>O<sub>34</sub>(OH)<sub>3</sub>)<sub>2</sub>]<sup>11-</sup> (<b>1</b>) has been synthesized and
characterized by IR, elemental analysis, SQUID magnetometry, electron paramagnetic resonance (EPR), and
electrochemistry. Single-crystal X-ray analysis was carried out on Cs<sub>4</sub>Na<sub>7</sub>[Fe<sub>6</sub>(OH)<sub>3</sub>(<i>A</i><i>-</i>α<i>-</i>GeW<sub>9</sub>O<sub>34</sub>(OH)<sub>3</sub>)<sub>2</sub>]·30H<sub>2</sub>O,
which crystallizes in the monoclinic system, space group <i>C</i><sub>2/<i>m</i></sub>, with <i>a</i> = 36.981(4) Å, <i>b</i> = 16.5759(15) Å, <i>c</i> =
16.0678(15) Å, β = 95.311(3)°, and <i>Z</i> = 4. Polyanion <b>1</b> consists of two (<i>A-</i>α<i>-</i>GeW<sub>9</sub>O<sub>34</sub>) Keggin moieties linked
via six Fe<sup>3+</sup> ions, leading to a double-sandwich structure. The equivalent iron centers represent a trigonal prismatic
Fe<sub>6</sub> fragment, resulting in virtual <i>D</i><sub>3</sub><i><sub>h</sub></i> symmetry for <b>1</b>. Electrochemistry studies revealed that <b>1</b> is stable in solution
from pH 3 to at least pH 7. In pH = 3 media the reduction of the six Fe<sup>3+</sup> centers was featured by a single
voltammetric wave for most supporting electrolytes used. In that case, whatever the scan rate from 1000 mV·s<sup>-1</sup>
down to 2 mV·s<sup>-1</sup>, no splitting of the single Fe-wave of <b>1</b> was observed. The acetate medium induced a partial
splitting of the wave, and this separation is enhanced with increasing pH. Remarkable efficiency of <b>1</b> in the
electrocatalytic reduction of nitrite, nitric oxide, and nitrate is demonstrated. Magnetic susceptibility (χ) measurements
indicate a diamagnetic (<i>S</i><sub>T</sub> = 0) ground state, with an average <i>J</i> = −12 cm<sup>-1</sup> and <i>g</i> = 2.00. EPR studies confirm
that the ground state is indeed diamagnetic, since the EPR signal intensity steadily decreases without any line
broadening as the temperature is lowered and becomes unobservable below about 50 K. The signal is a single
broad peak at all frequencies (90−370 GHz), ascribed to the thermally accessible excited states. Its <i>g</i><sub>iso</sub> is 1.992 51,
as expected for a high-spin Fe<sup>3+</sup>-containing species, and supports the χ data analysis.
2005-02-21 00:00:00
GeW 9 O 34
χ data analysis
D 3 h symmetry
OH
EPR signal intensity
Cs 4 Na 7
pH
2.00. EPR studies
Fe 6
prismatic Fe 6 fragment
IR
4. Polyanion 1
equivalent iron centers