Hydrogen-bonded anionic layer structures constructed from 4,4?-biphenyldicarboxylate and water molecules, and also with urea as an additional component

The crystal engineering of four new layer-type molecular solids is described. The anionic host layer in 2(Et4N+)·[4,4′-(C6H4)2(COO−)2]·4H2O (1) is constructed from 4,4′-biphenyldicarboxylate (BPDC) and a square (H2O)4 cluster through O—H···O and C—H···O hydrogen bonds. A hydrogen-bonded [(H2O)8O4] cluster connects BPDC ions through O—H···O linkages to form an anionic layer in 2[(n-Pr)4N+]·[4,4′-(C6H4)2(COO−)2]·8H2O (2). In 2[(n-Pr)4N+]·[4,4′-(C6H4)2(COO−)2]·2[(NH2)2CO]·4H2O (3) and 2[(n-Bu)4N+]·[4,4′-(C6H4)2(COO−)2]·­2[(NH2)2CO]·4H2O (4), BPDC forms analogous hydrogen-bonding patterns with urea and water molecules through N—H···O and O—H···O interactions, but the resulting anionic layers are pleated and nearly planar, respectively. Tetraalkylammonium cations are sandwiched between layers as guest species in all four structures.