W0146

Design of Robust Molecular Layers Using Ionic Hydrogen Bonds and Metal-Ligand Interactions. John C. MacDonald, Department of Chemistry, Northern Arizona University, Flagstaff, AZ 86001 USA

Organization of molecules into well-defined, predictable structures is a necessary step toward the design of crystalline materials that exhibit useful physical and mechanical properties. Our approach to crystal engineering attempts to simplify the packing of molecules by aligning them in two dimensions to form layers. The design for layers utilizes both hydrogen bonds and metal-ligand bonds to direct the assembly of molecules. In the absence of metals, the layer motif is based on the network of hydrogen bonds present in salts between imidazole and carboxylic acids. A series of imidazolium carboxylate salts have been crystallized and their structures determined in the solid state. In the presence of metals, different layer motifs were generated based on a combination of ionic hydrogen bonds and metal-ligand bonds. Several salts crystallized in layered motifs that were polar. These structures can be rationalized on the basis of steric repulsion, principles of closest packing, and maximizing hydrogen-bonding interactions with imidazolium cations. In all structures, imidazolium cations acted as multidentate hydrogen-bonding donors by forming two strong N-H^...O hydrogen bonds and from one to three C-H^...O interactions. Most of the C-H groups present on the imidazolium cations formed close interactions to oxygen with H^...O distances less than 2.7 Å. These interactions were extremely short (C^...O < 3.10 Å and H^...O < 2.25 Å) in several structures.