Supramolecular behavior of an isomorphous series of five bis(2-methylimidazolium 2,6-dicarboxypyridine) M(II) complexes

The supramolecular chemistry and crystal structures of five bis(2-metliylimidazolium 2,6-dicarboxypyridine) M(II) complexes, where M = Zn, Cu, Ni, Co, and 7:3 Mn/Cu (1-5, respectively), are reported. These complexes form building blocks with nearly identical molecular structures that crystallize in the same packing pattern. Anions of 2,6-dicarboxypyridine and cations of 2-methylimidazole form N-H(...)O and O-H(...)O hydrogen bonds that dominate crystal packing by forming linear ribbons of molecules. Thus, complexes 1-5 form an isomorphous series with a single robust crystalline architecture that accommodates five different transition metals without altering molecular packing. The growth of crystals from solutions that contain two different metal complexes produces mixed crystals in which mixtures of the different metal complexes are incorporated in the same relative molar ratio present in solution. This technique was used to grow crystals of 5 with Mn and Cu complexes in a 7:3 molar ratio. Complexes 1-5 form crystalline solids that represent a novel class of modular materials in which the organic ligands serve as a structural component that defines a single packing arrangement that persists over a range of structures and in which the metal serves as an interchangeable component with which to vary the physical properties of the material. The molecular and crystal structures of bis(2-methylimidazolium 2,6-dicarboxypyridine) M(II) complexes 1-5 are reported and compared to those of a related family of bis(imidazolium 2,6-dicarboxypyridine) M(II) dehydrate complexes 1'-5' (M = Zn, Cu, Ni, Co, and Mn) reported previously. We show that complexes 1-5 and 1'-5' have similar packing arrangements and that introducing a methyl substituent (similar in size to water) at the C2 position of imidazole displaces water and prevents it from being incorporated into the lattice of 1-5.