Crystals of the molecular silver nanoparticle Na4Ag44(pMBA)30 are the first molecular framework materials made from nanoparticles, which is a new class of materials. Approximately 50% of the volume of the crystal is void space. When compressed, the crystal becomes a molecular machine with concerted mechanical motion of its building blocks. This surprising and dramatic collective motion leads to a negative Poisson ratio. Auxetic materials such as this are very rare and can have very different properties than conventional materials. A mechanical study of this material appears in the August 2014 issue of Nature Materials.
The crystal structure of individual Na4Ag44(pMBA)30 molecular nanoparticles is also very important as it gives the first detailed view of the Ag-S interface, which is extremely important for understanding the nature and chemistry of thiolated silver nanoparticles. It also happens that this nanoparticle is the first to be produced on a massive scale in pure form, with a 140 gram batch demonstrated. Further, this nanoparticle is anomalously stable, more stable than even gold nanoparticles of the same class. This was reported in the September 19, 2013 issue of Nature.
The Na4Ag44(pMBA)30 crystal structure is my favorite for what it is and for what it can DO.—Terry Bigioni