Polymorphism and Inclusion Properties of Three-Dimensional Metal-Organometallic Frameworks Derived from a Terephthalate Sandwich Compound

An organometallic sandwich compound of terephthalic acid, namely, [(η5-Cp)FeII{η6-(1,4-C6H4(COOH)2)}]+ (H21+), is reported, along with X-ray single crystal structures of [H1·H21][PF6] and H1. [H21·H1][PF6] was reacted with the nitrate salts of CoII and NiII to yield a series of three-dimensional (3D) metal-organometallic framework (MOMF) materials of the composition [M3(1)4(μ-H2O)2(H2O)2][NO3]2·xsolvent (M = CoII (2), NiII (3); xsolvent = 4EtOH, or 2DMF·2H2O). 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]+ groups are arranged within the two-dimensional, square grid sheets of the 3D networks. α-2-EtOH, β-2-EtOH, α-3-EtOH, β-2-DMF, and β-3-DMF were thermally desolvated, giving rise to isolable apohosts of composition [M3(1)4(μ-H2O)2(H2O)2][NO3]2 (M = CoII (2), NiII (3)) 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 (