Metallapolyynes: Archetypes for Understanding and Rationally Designing Conjugated Transition-Metal Compounds and Materials

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Dr. Michael D. Hopkins, Department of Chemistry, University of Pittsburgh, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division for the study of conjugated transition metal compounds and materials. The project aims to answer two questions: (1) How does metal-for-carbon substitution affect the electronic structures of pi-conjugated organic compounds? and (2) What implications does this hold for improving the technological properties of these materials? A series of polyynes in which carbon atoms are systematically replaced by metal centers will be prepared and their bonding probed by electronic and vibrational spectroscopy, electrochemistry, and X-ray crystallography. Initially the study will concentrate on simple compounds in order to establish fundamental structural and bonding properties of metal-ligand multiple bonds. Then increasingly complex compounds, which potentially contain metal atoms within conjugated pi systems, will be studied in order to assess the nature and extent of a metal atom's participation in delocalized bonding networks. Variables to be investigated include the nature of the metal, its ligands and oxidation state, the length of the polyyne chain, and the number and distribution of metal centers within the pi network. This work is significant at a fundamental level because the proposed compounds represent a rare opportunity to examine systems that can be theoretically described both using models commonly employed for organic and others that are more appropriate for inorganic systems. The outcome will be conceptual bridges to link the two ways of considering the electronic structure of molecules. From a more practical viewpoint, the results will be applicable to the design of optical and electronic materials. Because of close structural and electronic relationship between the metallapolyynes prepared in this investigation and the conjugated organic materials currently used in a number of applications, the correlations established during this project will allow the technologically valuable properties of latter to be extended in a rational fashion to the former. Two specific properties of metallapolyynes that will be developed are intramolecular electronic coupling and nonlinear optical responses.