Seminar: Dr. Thomas Vaid (University of Alabama)

Dr. Thomas Vaid from the University of Alabama will present “Main-Group Porphyrin Complexes, Including a (C=C)-Centered Porphyrin; Semiconducting Inorganic-Organic Hybrid Frameworks.”

Abstract:  The organic ring systems of porphyrin and phthalocyanine complexes have long been known to be electrochemically redox-active, and we have taken advantage of that redox activity to isolate oxidized and reduced (yet neutrally charged) main-group porphyrin and phthalocyanine complexes.  For example, the radical aluminum tetraphenylporphyrin bis(tetrahydrofuran), Al(TPP)(THF)2, was synthesized and structurally characterized, and found to undergo a Jahn-Teller distortion that leads to alternating shortened and lengthened C‑C bonds on the porphyrin ring periphery, an effect that had not been observed previously.  In Si(TPP)(THF)2 both structural and spectroscopic data indicate that the doubly reduced porphyrin is a 20 pi-electron antiaromatic system :  its ring system has alternating single and double C-C bonds, with a strong paratropic ring current evident in its NMR spectra.  Aromatic GeII(TPP) undergoes a remarkable reversible reaction with pyridine, forming antiaromatic GeIV(TPP)(py)2.  The doubly oxidized [Li(TPP)][BF4] contains an antiaromatic 16 pi-electron circuit.  Similar results concerning phthalocyanine complexes will be presented.

The vast majority of known metal-organic frameworks (MOFs) are electrically insulating, and there has been increasing interest in the creation of conducting MOFs, which could find use in high-surface-area electrodes and other applications.  In most MOFs the linkage between the metal and bridging ligand is formed by oxygen or nitrogen.  In analogy in to inorganic sulfides and selenides, MOFs containing sulfur or selenium are likely to have smaller band gaps and therefore more likely to be electrically conducting.  We have synthesized several sulfur and selenium-containing nonporous MOFs, and will discuss the salient structural features and electrical properties.