Supramolecular isomers in the same crystal: a new case involving two different types of layers polycatenated in the 3D architecture of [Cu(bix)2(SO4)]·7.5H2O [bix=1,4-bis(imidazol-1-ylmethyl)benzene]

The reactions of copper(II) sulfate with the flexible ligand 1,4-bis(imidazol-1-ylmethyl)benzene (bix) in H2O/acetone solution have afforded two novel coordination polymers, i.e. the 1D species [Cu(bix)(H2O)3(SO4)]?H2O and the 3D networked array [Cu(bix)2(SO4)]?7.5H2O. The former polymer contains highly undulated chains that are joined into 2D layers via hydrogen bond bridges. The second species shows an unusual 3D architecture comprised of two interlocked sets of different 2D layers, giving inclined polycatenation. Both sets of layers display the same (4,4) topology but exhibit quite different tiling patterns (with ‘ideal’ plane symmetry c2mm and p4gm, respectively) because of the varied conformations of the bix ligands on passing from the first set to the second one. These two 2D motifs represent a new case of supramolecular isomerism in the same crystal. The sulfate anions form m2-bridges between copper ions, that cross-link the two sets of layers, giving a single 3D self-penetrating 6-connected network. This shows channels (total free void ca. 27% of the cell volume) containing many solvated water molecules, that are lost upon thermal activation and regained with crystal modification. A brief analysis of the known examples of supramolecular isomers contained in the same crystal is also reported.