Polymorphism and Inclusion Properties of Three-Dimensional Metal-Organometallic Frameworks Derived from a Terephthalate Sandwich Compound
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posted on 2009-07-20, 00:00 authored by Sayon A. Kumalah, K. Travis HolmanAn organometallic sandwich compound of terephthalic acid, namely, [(η<sup>5</sup>-Cp)Fe<sup>II</sup>{η<sup>6</sup>-(1,4-C<sub>6</sub>H<sub>4</sub>(COOH)<sub>2</sub>)}]<sup>+</sup> (H<sub>2</sub><b>1</b><sup>+</sup>), is reported, along with X-ray single crystal structures of [H<b>1</b>·H<sub>2</sub><b>1</b>][PF<sub>6</sub>] and H<b>1</b>. [H<sub>2</sub><b>1</b>·H<b>1</b>][PF<sub>6</sub>] was reacted with the nitrate salts of Co<sup>II</sup> and Ni<sup>II</sup> to yield a series of three-dimensional (3D) metal-organometallic framework (MOMF) materials of the composition [M<sub>3</sub>(<b>1</b>)<sub>4</sub>(μ-H<sub>2</sub>O)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][NO<sub>3</sub>]<sub>2</sub>·<i>x</i>solvent (M = Co<sup>II</sup> (<b>2</b>), Ni<sup>II</sup> (<b>3</b>); <i>x</i>solvent = 4EtOH, or 2DMF·2H<sub>2</sub>O). These framework structures were shown by single crystal and powder X-ray diffraction to be polymorphic, possessing identical 3D body-centered tetragonal network topologies, but differing in the manner by which the [CpFe]<sup>+</sup> groups are arranged within the two-dimensional, square grid sheets of the 3D networks. <b>α-2-EtOH</b>, <b>β-2-EtOH</b>, <b>α-3-EtOH</b>, <b>β-2-DMF</b>, and <b>β-3-DMF</b> were thermally desolvated, giving rise to isolable apohosts of composition [M<sub>3</sub>(<b>1</b>)<sub>4</sub>(μ-H<sub>2</sub>O)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][NO<sub>3</sub>]<sub>2</sub> (M = Co<sup>II</sup> (<b>2</b>), Ni<sup>II</sup> (<b>3</b>)) that were shown by PXRD to possess different, as yet unknown, crystal structures. The desolvated apohosts were studied with respect to their ability to selectively reabsorb water and/or alcohols. They show a modest preference for the absorption of water and short chain, linear alcohols (
