A Rational Study of Crystal Engineering of Supramolecular Assemblies of 1,2,4,5-Benzenetetracarboxylic Acid

Supramolecular assemblies of 1,2,4,5-benzenetetracarboxylic acid, <b>1</b>, with <i>aza</i> donor molecules such as 1,10-phenanthroline, <b>2</b>, 1,7-phenanthroline, <b>3</b>, phenazine, <b>4</b>, 4-(<i>N</i>,<i>N</i>-dimethylamino)pyridine, <b>5</b>, 1,2-bis(4-pyridyl)ethene, <b>6</b>, and 1,2-bis(4-pyridyl)ethane, <b>7</b>, have been synthesized and characterized by single-crystal X-ray diffraction methods. All the complexes crystallize in the triclinic, <i>P</i>1̄ space group. In the complexes of <b>2</b> and <b>4</b>, water is also present in the resultant assembly, but the complexes of <b>5</b>, <b>6</b>, and <b>7</b> crystallize without any water molecules or solvent of crystallization. However, <b>3</b> forms two types of complexes, a hydrate and a nonhydrate complex, depending upon whether water is used as a solvent or not. These assemblies divide into two classes, host−guest systems (with aza molecules being in the channels created by the acid molecules) and assemblies with infinite molecular tapes. While the assemblies of the compounds <b>2</b>, <b>4</b>, and <b>5</b> belong to the former class, the assemblies of compounds <b>6</b> and <b>7</b> form molecular tapes, which are arranged in two dimensions to form sheet structures. The two structures of <b>3</b>, in fact, bridge the two classes with each one falling into different categories.