Hydrogen Bond-Directed Frameworks Based on 1,2,4,5-Benzene-Tetracarboxylate

The deprotonated forms of 1,2,4,5-benzenetetracarboxylic acid H 4 bta can act not only as hydrogen-bond acceptors but also as hydrogen-bond donors, depending on the deprotonated carboxyl groups given different supramolecular adducts. A search of the Cambridge Structural Database (CSD) of cocrystal structures of H 4 bta with L = 4,4‘-bpy or bpe has found three different adducts: [HL] 2 [H 2 bta], [H 2 L][H 2 bta], and [H 2 L][H 3 bta], where cocrystal structures of [HL] 2 [H 2 bta] with L = 4,4‘-bpy or bpe form similar supramolecular arrangements. To investigate this similarity, two new organic salts of the formula {[H 2 -4,4‘-bpy][H 2 bta]}·2H 2 O ( 1 ) and {[H 2 bpe] [H 3 bta] 2 }·4H 2 O ( 2 ) have been characterized. In the 1:1 adduct 1, the molecular components are linked by hydrogen bonds of the N−H···O type creating chains. These chains are further linked by C−H···O type interactions (C−H from the cation and O from the anion) creating a two-dimensional motif. Two types of centrosymmetric rings are evident in the sheets. The stacked sheets are held together via π···π interactions to create a three-dimensional network. Two types of channels, one hydrophilic and the other hydrophobic, run parallel to the a -axis. Water molecules are hydrogen bonded in the hydrophilic channels. The supramolecular structure in the 2:1 adduct 2 is due to hydrogen bonds of the O−H···O and N−H···O types that afford a railroad network along the a -axis. Two water molecules are held in the railroad cavities by hydrogen bonds with carboxylate oxygen atoms. Adjacent railroad chains are linked through hydrogen bonds involving water molecules, building a two-dimensional structure.