CMSS Colloquium: Molecular Silver Nanoparticles: chemical, optical and structural principles, Feb. 5

Terry Bigioni

The Condensed Matter & Surface Sciences Colloquium Series presents Terry Bigioni on “Molecular Silver Nanoparticles: chemical, optical and structural principles” on Thursday, Feb. 5, at 4:10 p.m. in Walter Lecture Hall 245.

Abstract: Very small noble metal nanoparticles have molecular forms, i.e. they have definite molecular formulae and structures, which have been determined by mass spectrometry and single-crystal x-ray diffraction, respectively. Current models cannot account for the chemical and physical properties of these complex and structurally diverse materials. Contemporary thinking is that nanoparticle stability is determined only by the details of the metal core. Further, no model for predicting molecular structures yet exists. We have found that the outer protective ligand layer can play a determinant role in the structure and stability of molecular nanoparticles, selecting the core structure rather than simply passivating it. For example, families of molecular silver nanoparticles are produced with aliphatic ligands (e.g. glutathione, captopril, cysteine) whereas phenyl-containing ligands have been found to produce only a 44-atom Ag nanoparticle that is extremely stable and that is not observed with aliphatic ligands. The unprecedented stability of this nanoparticle resulted in (i) a truly single-sized molecular product, (ii) ~140 g of pure product from a single batch, and (iii) an opportunity to crystallize the nanoparticle and understand its protective ligand shell, atomic and electronic structure, and thereby its stability. Notably, this has provided key insights into the stability of silver nanoparticles, which has been a major obstacle, as well as the structural principles that govern all molecular metal nanoparticles. Finally, the nanoparticle molecular crystal has a framework structure that is predicted to have very unusual mechanical properties, with both structure and response being controlled by the ligands. From these results it is evident that ligands can have a very significant effect on the materials synthesized and in fact, with judicious choices, they can be used as multiscale structure-directing synthons.