New Cyanometalate Building Units: Synthesis and Characterization of [Re(CN)<sub>7</sub>]<sup>3-</sup> and [Re(CN)<sub>8</sub>]<sup>3-</sup>

2003-02-07T00:00:00Z (GMT) by Miriam V. Bennett Jeffrey R. Long
Two new cyanorhenate complexes of potential utility in constructing magnetic and photomagnetic materials are reported. Reaction of (Bu<sub>4</sub>N)CN with [ReCl<sub>6</sub>]<sup>2-</sup> in acetonitrile affords yellow (Bu<sub>4</sub>N)<sub>3</sub>[Re(CN)<sub>7</sub>] (<b>1</b>), featuring the pentagonal bipyramidal complex [Re(CN)<sub>7</sub>]<sup>3-</sup>. The spectral and magnetic properties of <b>1</b> indicate that the complex has an <i>S</i> = 1/2 ground state with considerable anisotropy in the <i>g</i> tensor. In aqueous solution, <b>1</b> reacts with Mn<sup>2+</sup> ions to generate the three-dimensional cyano-bridged solid [<i>fac</i>-Mn(H<sub>2</sub>O)<sub>3</sub>][<i>cis</i>-Mn(H<sub>2</sub>O)<sub>2</sub>][Re(CN)<sub>7</sub>]·3H<sub>2</sub>O (<b>2</b>) containing diamagnetic [Re(CN)<sub>7</sub>]<sup>4-</sup>. Addition of KIO<sub>4</sub> to the reaction solution, originally intended to prevent reduction of the rhenium during solid formation, instead yields white (Bu<sub>4</sub>N)<sub>3</sub>[Re(CN)<sub>8</sub>] (<b>3</b>). As crystallized in K<sub>3</sub>[Re(CN)<sub>8</sub>]·2MeCN (<b>4</b>·2MeCN), the diamagnetic [Re(CN)<sub>8</sub>]<sup>3-</sup> complex adopts a nearly perfect square antiprismatic coordination geometry. In solution, this species behaves analogously to the isoelectronic [M(CN)<sub>8</sub>]<sup>4-</sup> (M = Mo, W) complexes, apparently converting to a dodecahedral geometry and photooxidizing under UV radiation to give paramagnetic [Re(CN)<sub>8</sub>]<sup>2-</sup>.