Digestive ripening: a synthetic method par excellence for core-shell, alloy, and composite nanostructured materials

The solvated metal atom dispersion (SMAD) method has been used for the synthesis of colloids of metal nanoparticles. It is a top-down approach involving condensation of metal atoms in low temperature solvent matrices in a SMAD reactor maintained at 77 K. Warming of the matrix results in a slurry of metal atoms that interact with one another to form particles that grow in size. The organic solvent solvates the particles and acts as a weak capping agent to halt/slow down the growth process to a certain extent. This as-prepared colloid consists of metal nanoparticles that are quite polydisperse. In a process termed as digestive ripening, addition of a capping agent to the as-prepared colloid which is polydisperse renders it highly monodisperse either under ambient or thermal conditions. In this, as yet not well-understood process, smaller particles grow and the larger ones diminish in size until the system attains uniformity in size and a dynamic equilibrium is established. Using the SMAD method in combination with digestive ripening process, highly monodisperse metal, core-shell, alloy, and composite nanoparticles have been synthesized. This article is a review of our contributions together with some literature reports on this methodology to realize various nanostructured materials.

Characterization of Interactions Involving Bromine in 2,2-Dibromo2,3-dihydroinden-1-one via Experimental Charge Density Analysis

Experimental and theoretical charge density analyses on 2,2-dibromo-2,3-dihydroinden-1-one have been carried out to quantify the topological features of a short CBr....O halogen bond with nearly linear geometry (2.922 angstrom, angle CBr....O = 172.7 degrees) and to assess the strength of the interactions using the topological features of the electron density. The electrostatic potential map indicates the presence of the s-hole on bromine, while the interaction energy is comparable to that of a moderate OH....O hydrogen bond. In addition, the energetic contribution of CH.....Br interaction is demonstrated to be on par with that of the CBr....O halogen bond in stabilizing the crystal structure.