Cobalt, Manganese, Nickel, and Vanadium Derivatives of the Cyclic 48-Tungsto-8-Phosphate [H<sub>7</sub>P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>]<sup>33−</sup>

The cobalt(II) containing tungstophosphate [Co<sub>4</sub>(H<sub>2</sub>O)<sub>16</sub>P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>]<sup>32−</sup> (<b>1</b>) has been synthesized by addition of Co<sup>2+</sup> ions to an aqueous solution of [H<sub>7</sub>P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>]<sup>33−</sup> (<b>P</b><sub><b>8</b></sub><b>W</b><sub><b>48</b></sub>) and characterized by single-crystal XRD, IR, and UV−vis spectroscopy, elemental analysis, electrochemistry, and magnetochemistry. The novel polyanion <b>1</b> is a derivative of the superlacunary <b>P</b><sub><b>8</b></sub><b>W</b><sub><b>48</b></sub> with four cobalt(II) ions coordinated to the rim of the central cavity and two additional cobalt(II) ions linked on the outside bridging neighboring polyanions. Using similar synthetic procedures, but adding a few drops of H<sub>2</sub>O<sub>2</sub>, we isolated the manganese(II) derivative [Mn<sub>4</sub>(H<sub>2</sub>O)<sub>16</sub>(P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>)(WO<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>)<sub>2</sub>]<sup>28−</sup> (<b>2</b>) and its nickel(II) analogue [Ni<sub>4</sub>(H<sub>2</sub>O)<sub>16</sub>(P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>)(WO<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>)<sub>2</sub>]<sup>28−</sup> (<b>3</b>). Both polyanions have picked up two equivalents of tungsten resulting in the unprecedented {P<sub>8</sub>W<sub>50</sub>} host framework. We also made the vanadium(V) derivative [(VO<sub>2</sub>)<sub>4</sub>(P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>)]<sup>36−</sup> (<b>4</b>), with four tetrahedral vanadate groups grafted to the <b>P</b><sub><b>8</b></sub><b>W</b><sub><b>48</b></sub> host. The voltammetric patterns associated with the W-centers in polyanions <b>1</b>, <b>2</b>, and <b>4</b> display enough distinct features allowing for a qualitative classification according to relative basicity of the reduced polyanions: <b>2</b> > <b>P</b><sub><b>8</b></sub><b>W</b><sub><b>48</b></sub> > <b>1</b> > <b>4</b>. The electrochemistry of <b>1</b> offers a new example for detection of the Co<sup>2+</sup> centers in a multicobalt containing polyanion. During a study of the Mn<sup>2+</sup> centers of <b>2</b> at pH 5, a film deposition is observed. The vanadium(V) centers of <b>4</b> are well-behaved in a pH 0.33 medium. Temperature and magnetic field dependence of the magnetic moment of <b>1</b>−<b>3</b> were performed on a SQUID magnetometer over the temperature range 1.8−250 K and field range 0−7 T. The results are consistent with the model of noninteracting 3d metal ions. Variable temperature (4−295 K) and variable frequency (34−413 GHz) EPR measurements support the magnetic susceptibility results. The zero-field splitting <i>D</i> and <i>g</i> values obtained for <b>1</b>−<b>3</b> are in agreement with those reported for high-spin Co<sup>2+</sup>, Mn<sup>2+</sup>, and Ni<sup>2+</sup> ions in axially distorted octahedral environments.