Syntheses and characterizations of extended diruthenium polyyn-diyls and trans-[Fe(cyclam)(C[equiv]CR)2]+ as building blocks for molecular wires

Zhi Cao, Purdue University

Abstract

Over the past decades, extensive interest has been focused on the development of new carbon-rich organometallic materials containing π-conjugated oligomers, due to the unique optical and electronic properties. Those organometallic oligo/polymers are superior to the organic analogs and widely used as semiconductors, electrochemical and fluorescent sensors, field effect transistors, molecular electronics, upon extensive modifications for the coordination spheres of the metal centers. The primary focus of my dissertation is on the synthesis and characterization of carbon-rich organometallic materials, especially metal-alkynyl compounds with extended π conjugation. The first examples of Fe(III)-alkynyl complexes based on the Fe(III)-cyclam motif are well established, strong π-interactions between the occupied dπ and π(C≡C) orbitals are evident from both the spectroscopies and DFT calculations. These type of compounds generally display intense and structured bands in the visible absorption spectra, which are assigned as spin-allowed d-d transitions. Efforts are also devoted to explore the feasibility of constructing molecular wires based on gem-diethynylethene (gem-DEE) bridged 3d transition metal oligomers from a theoretical perspective. Among the constructed first-row transition metal complexes, extensive interactions between the dπ orbitals and π(DEE) orbitals were found for the V, Cr and Fe compounds. A detailed natural bond orbital (NBO) analysis revealed that the electronic delocalization in [M]-gem-DEE-[M] is attributed to both the σ orbitals along the DEE backbone and π orbitals perpendicular to the DEE plane. First examples of redox-active Fe(III) cyclam compounds based on gem-DEE ligands have been subsequently synthesized upon this foundation, with the gem-DEE ligand being proved as a better π electron donor in comparison with linear alkynyl ligands. Additional effort was directed towards the synthesis, structural characterization, voltammetric, spectroscopic, and spectroelectrochemical studies of extended family of wire-like molecules, [Ru2](μ-C 2m)[Ru2] ( m= 4-10 ). Significant electronic coupling was evident from variety of spectroscopic and theoretical characterizations on the polyyn-diyl bridged dimer compounds. The small electronic coupling attenuation constants suggests polyyn-diyl bridges are efficient mediating charge transfer.

Degree

Ph.D.

Advisors

Ren, Purdue University.

Subject Area

Inorganic chemistry

COinS