Chiral nanocluster with open shell electronic structure and helical face-centered cubic framework

Silver nanoparticles (AgNPs) constitute an important type of nanomaterial for a variety of innovative applications. The antibactericidal and antifungicidal activities of AgNPs have gained an increasing interest for their applications in coatings, textiles, wound treatment, sterilization, and biomedical devices. The use of nano-silver reduces cytotoxicity but not antibacterial/ antifungal efficacy—an attractive feature attributed to the formation of free radicals from the surface of the nanoparticles. The properties of AgNPs are strongly influenced by their morphology, size, shape, aggregation state, and surface engineering. Therefore, systematic development of AgNPs is required for optimization of the nanoparticles for specific applications, e.g., selective destruction of cancer cells. In this regard, significant efforts have been made to synthesize and characterize ultrasmall-sized Ag metalloid and Ag(I) nanoclusters.

Despite the great advances in the synthesis, the total structure determination of nanoclusters still remains to be a major challenge. Recently Hyung J. Kim and their colleagues have reported the synthesis and crystal structure of a nanocluster composed of silver atoms capped by 8 phosphine and 18 phenylethanethiolate ligands in the journal of Nature Communications.

They have devised a synthetic approach for Ag23(PPh3)8(SC2H4Ph)18 and solved its crystal structure. By using x-ray crystallographic analysis, they have revealed that the kernel of the Ag nanocluster adopts a helical face-centered cubic structure with C2 symmetry. No counter ion (e.g., Na+ and NO3) is found in the single-crystal and the absence of such ions is also confirmed by X-ray photoelectron spectroscopy analysis, indicating electrical neutrality of the nanocluster. Interestingly, the nanocluster has an open shell electronic structure (i.e., 23(Ag 5s1)–18(SR) = 5e), as confirmed by electron paramagnetic resonance spectroscopy. Time-dependent density functional theory calculations are performed to correlate the structure and optical absorption/emission spectra of the Ag nanocluster.

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