Lightweight Ionic Networks Composed of Li⁺ or Mg²⁺ Centres Linked Together by Dicarboxylate Ligands

The combination of lightweight metal cations with a range of dicarboxylate ligands has led to the generation of ionic network materials that possess channels occupied by solvent molecules. The compounds [Li₂ (2,2-bpdc)(DMF)₂ ] and [Mg(2,2-bpdc)(DMF)₂ ] (2,2-bpdc=2,2-dipyridyl-4,4-dicarboxylate) adopt a similar structure in which parallel metal-carboxylate chains are linked to four equivalent chains to generate a 3 D network in which DMF molecules occupy channels. [Li₄ (3,5-pdc)₂ (DMF)]⋅solvate (3,5-pdc=3,5-pyridine dicarboxylate) adopts a similar structure but the chains are more complex. As with the other structures, coordinated DMF molecules occupy network channels. [Li₄ (3,5-pdc)₂ (DMF)]⋅solvate is able to adsorb carbon dioxide at elevated pressures with the adsorption following a type V isotherm; hysteresis is apparent upon desorption. The final compound, Li[Mg₃ OH(2,2-bqdc)₃ (DMF/H₂ O)₃ ]⋅solvate (2,2-bqdc=2,2-biquinoline-4,4-dicarboxylate) has a distinctly different structure in which a trio of magnesium centres bound to a central μ₃ -hydroxide ion serves as a 6-connecting, trigonal prismatic node within a 3 D network that has the point symbol, 4⁹ 6⁶ . Solvent-filled intraframework spaces represent over 50 % of the crystal volume and are occupied by highly disordered solvent and Li⁺ ions. Immersion of Li[Mg₃ OH(2,2-bqdc)₃ (DMF/H₂ O)₃ ]⋅solvate in a solution of Fe(2,2-bipyridine)₃ ²⁺ results in the incorporation of the Fe^II complex into the large channels of the anionic network.