Procter & Gamble–UCLA Student Organization for Cultural Diversity in Chemistry Lecture: “Size, Shape and Electronic Complementarity Between the Carbon Cages and the Clusters in Endohedral Fullerenes”

Seminar series
Organic Colloquium
When
Thu, Apr 17 5:00pm
Where
Cram Conference Room – 3440 Molecular Sciences Bldg
Speaker Professor Luis A. Echegoyen
University of Texas at El Paso
Department of Chemistry
Description

Procter & Gamble–UCLA Student Organization for Cultural Diversity in Chemistry Lecture

“Size, Shape and Electronic Complementarity Between the Carbon Cages and the Clusters in Endohedral Fullerenes”

Abstract.  A while back we reported a series of trimetallic nitride endohedral fullerenes containing Gd3N, Pr3N, Nd3N, Ce3N and La3N inside carbon cages that ranged between C78 and C96. The relative abundances of these cages as well as the electrochemical properties are a pronounced function of the size of the encapsulated metal cluster. M3N@C88 compounds predominate for Nd, Pr and Ce and these exhibit surprisingly reversible electrochemical properties and extremely low bandgaps, yet contradictorily low reactivities. In the case of M3N@C78, M3N@C82 and M3N@C84, the observed cages violate the IPR rule and these are independent of the nature of the metal inside. More recently we have discovered a new and very large family of endohedral compounds containing dimetallic sulfide as the encapsulated cluster, M2S@C2n, with cages ranging from C70 to C100. The X-Ray single crystal of Sc2S@C82 (CS) is the first determined for an endohedral compound to possess complete order of the cage as well as of the cluster inside, providing exquisite detail of the interplay between the geometry of the cage and that of the cluster inside, including the Sc-S-Sc angle. The Sc2S@C82 (C3V) crystal structure exhibited an ordered cage but some cluster disorder, and the Sc-S-Sc angle was observed to be very different from that of the CS isomer. Very recent X-Ray crystallographic results for another member of the scandium sulfide family, Sc2S@C72, indicates the presence of a never reported C72 cage with two IPR violations and, as usual, the two pentalene units are adjacent to the two Sc ions. The cage selected is isomer 10,528 out of 11,190 (C72 has only one IPR isomer). Very recently we found that Sc2S@C70 possesses a carbon cage that has never been reported before, cage #7,892, with two IPR violations. Within this family we have also identified two new isomers of Sc2S@C80, and from their UV-Vis spectra we know that these are cages that have never been reported before.

              A new endohedral compound was recently isolated and characterized, Ti2S@C78, as well as a totally new family of endohedrals, Sc2UC@C2n, where n=33, 35 and 40. This is a totally new metallic carbide family, where the entrapped cluster contains two formally 3+ ions (Sc), one formally 4+ ion (U) and a 4- carbon, forming an unusual carbide cluster. Some derivatives of these endohedral compounds have been prepared using a variety of synthetic techniques, and their properties have been examined, such as charge mobility and their photoresponses. Their properties as acceptors in Organic Solar Cells (OSCs) are being evaluated, since their LUMO levels can be controlled by the nature of the clusters entrapped and the size and isomeric composition of the carbon cages.

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