Bis(imidazolium 2,4,6-tricarboxypyridine) Metal(II) Complexes: Molecular Building Blocks that Generate Isomorphous Hydrogen-Bonded Frameworks

The supramolecular chemistry and crystal structures of four bis(imidazolium 2,4,6-tricarboxypyridine) metal(II)
trihydrate complexes, where M = Co, Ni, Cu, or Zn (1-Co, 1-Ni, 1-Cu, and 1-Zn, respectively) are reported. Complexes 1-Co,
1-Ni, 1-Cu, and 1-Zn have similar molecular structures that crystallize to give the same packing pattern. 2,4,6-Tricarboxypyridine
anions and imidazolium cations form strong N−H···O and O−H···O hydrogen bonds that dominate crystal packing by forming a
three-dimensional network of molecules. These complexes form an isomorphous series with a single crystalline architecture that fits
at least four different transition metals without changing molecular packing. Thus, these complexes are a family of modular materials
in which the organic components define a single packing arrangement that persists over a range of structures and in which the metal
serves as a component that can be changed. The molecular and crystal structures of bis(imidazolium 2,4,6-tricarboxypyridine) M(II)
complexes 1-Co, 1-Ni, 1-Cu, and 1-Zn are reported and compared to those of a related family of bis(imidazolium 2,6-dicarboxypyridine) M(II) complexes 2-Mn, 2-Co, 2-Ni, 2-Cu, and 2-Zn reported previously. We show that complexes 1-Co, 1-Ni,
1-Cu, and 1-Zn form layers of cations and anions similar to those in 2-Mn, 2-Co, 2-Ni, 2-Cu, and 2-Zn and that introducing a
CO2H group at the C4 position on the pyridine ring promotes additional acid−acid interactions that link and align adjacent layers.