Reports: UR351546-UR3: Polyaromatic Metal Complexes: Pathways to Graphene Sandwiches

Stephanie Hurst, PhD, Northern Arizona University


The objective of this research proposal (51546-UR3) was to explore and develop bonding geometries of platinum and palladium complexes to give unique one- and two-dimensional organometallic materials with a range of “tunable” properties.

During the course of this project we have successfully generated a new series of palladium complexes that contain a range of nitrogen containing ligands including pyridine and acetonitrile. These complexes are of interest as they inform us to the ability of these complexes to form larger structures. Large, regularly defined structures are of great interest as catalysts since the use of materials with large surface areas are critical to diverse industrial applications including the Haber-Bosch, octane cracking and other industrial processes. The interest in such materials has given rise to the creation of metal-organic frameworks (MOF) which may have significant application in gas separation and gas storage. Incorporating palladium-containing complexes enhances the functionality of such materials and gives the possibility of incorporating catalytic activity.

During the work of this project we have been able to crystallize several of these derivatives and to determine the bond lengths and angles of several of the complexes.  Palladium to nitrogen bond distances are show to be significantly longer in the pyridine derivatives in comparison with the nitrile derivatives, a key finding that assist in directing our research. This is analogous to our prior findings that show a progressive shift in Pd-X (X = P, As or Sb) bond lengths in a related class of complexes. We are now able to predict the most appropriate ligand moieties for the construction of large supramolecular structures, a key object of this work. It is our intention to use these large, repeating three-dimensional structures as a host material for the inclusions of small guest molecules. Single crystal X-ray diffraction studies of the host-guest complexes will allow us to study complexes that previously did not crystallize.

Our work in the synthesis of derivatives of dimetallic metal systems based on the [Pd2(dba)3] (dba = dibenzylideneacetone) system is ongoing. This simple complex is a critical catalyst used around the world and especially in the petroleum industry. The p-conjugated system of the dba ligand stabilizes two zero-valent palladium or platinum atoms via eta bonding, and our group have been optimizing the organic ligand backbone by systematic substitution with a range of alkyl and alkoxy groups.  We have observed systematic effects in both 1H NMR and UV-vis spectra as well as systematic changes in the metal-metal bond length via single-crystal X-ray diffraction analysis. We have encountered challenges including disorder in the orientation of the dba ligands but these structures shed considerable light on an area that is poorly studied despite its importance to industrial catalysis.

Of significant additional interest had been our work of converting crystallographic information framework (cif) files to three-dimensional tactile models. The rapid decreasing in price of three-dimensional printers in the past few years has heralded a range of new learning tools for undergraduate students. We have demonstrated a new methodology (currently under review) that allows for the rapid conversion of crystallographic information framework (cif) files to stereolithographic (stl) files that may be printed on a three-dimensional printer. Given the great importance that a strong visual ability has on success in chemistry, this new method allows for the fast and rapid creation of tactile models. Instead of piecing models together from single atoms and bonds, students can now routinely print models from existing data. We have applied this method to a range of crystallographically characterized materials including single-molecules, proteins and minerals.

In the past year we have had significant success with our undergraduate students presenting their results in a number of different forums. Many students have then used this experience to successfully apply to graduate schools in chemistry including Colorado State University, Tulane and other institutions.