Double Sandwich Polyoxometalate
and Its Fe(III) Substituted
Derivative, [As<sub>2</sub>Fe<sub>5</sub>Mo<sub>21</sub>O<sub>82</sub>]<sup>17–</sup> and [As<sub>2</sub>Fe<sub>6</sub>Mo<sub>20</sub>O<sub>80</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>16–</sup>
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Abstract
A double sandwich polyoxometalate and its Fe(III) substituted
derivative,
[As<sub>2</sub>Fe<sub>5</sub>Mo<sub>21</sub>O<sub>82</sub>]<sup>17–</sup> (<b>1</b>) and [As<sub>2</sub>Fe<sub>6</sub>Mo<sub>20</sub>O<sub>80</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>16–</sup> (<b>2</b>), were synthesized and characterized by single-crystal X-ray
diffraction, infrared spectroscopy, fluorescent spectroscopy, UV spectra,
thermogravimetry-differential scanning calorimetry analyses, electrospray
ionization mass spectrometry, and magnetism measurements. The polyoxoanion
is composed of a central fragment FeMo<sub>7</sub>O<sub>28</sub> for <b>1</b> (Fe<sub>2</sub>Mo<sub>6</sub>O<sub>26</sub>(H<sub>2</sub>O)<sub>2</sub> for <b>2</b>) and two external AsMo<sub>7</sub>O<sub>27</sub> fragments linked together by two distinct edge-sharing
dimeric clusters Fe<sub>2</sub>O<sub>10</sub> to lead to a <i>C</i><sub>2<i>v</i></sub> molecular symmetry. The
central FeMo<sub>7</sub>O<sub>28</sub> fragment and external AsMo<sub>7</sub>O<sub>27</sub> fragment have a similar structure, and both
of them can be viewed as a monocapped hexavacant α-Keggin subunit
with a central FeO<sub>4</sub> group or a central AsO<sub>3</sub> group.
Both of the polyoxoanions contain a oxo-bridged Fe<sup>III</sup><sub>5</sub> magnetic core with the angles of Fe–O–Fe in
the range of 96.4(4)–125.7(5)°, and magnetism measurements
show an overall ferromagnetic interactions among the five-nuclearity
cluster Fe<sub>5</sub> with the spin ground state <i>S</i> = 15/2
