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)Fe^II{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 Co^II and Ni^II 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 = Co^II (2), Ni^II (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 = Co^II (2), Ni^II (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 (