It is essential to understand the evolution pattern of a periodic series of nanocluster structures and their properties to rationalize the design of new nanoclusters for a specific function. The lack of inherent periodicity in size among nanoclusters make this study quite challenging. Here we report a successful transformation of the Au 28 (SR) 20 nanocluster, which is among the rare periodic series (gold quantum box) of gold nanoclusters, to the higher one in the series, the Au 36 (SR) 24 cluster. On the basis of the mechanistic study and characterization of byproducts of this reaction, we put forward the postulate that this process involves the breakage of the staple as well as the core of Au 28 (SR) 20 , followed by restructuring into Au 36 (SR) 24 .
Ligand
protected atom-precise gold-based catalysts have been utilized
in many essential chemical processes, but their mechanism and the
fate of the catalyst during reaction are still unrevealed. Atom-precise
cluster without ligands are thus highly desirable to maximize atom
efficiency, but making these in solution phase is challenging. In
this scenario, catalysts with dispersion on oxide support are highly
desirable to understand the role of metal core during catalytic reaction.
Here, we report the synthesis of Au11(PPh3)7I3 cluster that consists of an incomplete icosahedron
core. During its impregnation process on CeO2 support,
all of the ligands were removed from the kernel and the Au11 kernel fits into the defects of ceria (embedded onto the oxygen
vacancy of ceria (111) plane). This Au11@CeO2 has high atom efficiency and catalytic activity for Ullmann-type
C–C homocoupling reactions for electron rich substrates. Density
functional theory calculations showed that hexagonal arrangements
of Au11 kernel on (111) plane of CeO2 is the
most stable one. Theoretical calculations also proved that the atop
gold atom has more favorable interaction with phenyl iodide than the
second layer gold atoms of the Au11@CeO2. This
demonstrated that the present catalyst mimics the single-atom catalyst-like
behavior in facilitating the coupling reactions.
Small-sized silver nanoparticles are incorporated into a thiolfunctionalized stable Zr-based metal−organic framework (MOF). Thiol functionalization has been carried out using 2-mercapto benzoic acid (2-MBA) as the modulator, which promotes defect formation in the MOF structure. The incorporation of silver nanoparticles aided by the silver− sulfur interactions in this defective MOF gives rise to catalytic activity. Its catalytic efficiency in the highly atom-efficient A 3 coupling reaction has been studied for a variety of substrates with impressive recyclability. The synergistic effect of the electron-rich silver core and electron-deficient surface of the thiol-bonded silver nanoparticle is key for this catalytic reaction.
Atom precise metal nanoclusters with customized surface structures are important for understanding the mechanism of surface engineering for appropriate applications. We are reporting a single copper doping on a very widely studied Au 11 (PPh 3 ) 7 Cl 3 nanocluster, in which one chloride ligand is replaced by one Cu atom. Accordingly, a new bimetal nanocluster Cu 1 Au 11 (PPh 3 ) 7 Cl 2 is produced, which consisted of a unique Au− Cu surface motif where the Cu is only bonded with an Au atom. In such a motif, the unsaturated Cu atom acts as an active catalyst for the Sonogashira reaction in contrast to the catalytically inactive Au 11 nanocluster. Moreover, it demonstrated a reversed selectivity in the Sonogashira cross-coupling reaction, where the major product obtained was homocoupled Glaser products in contrast to the selectivity of previously reported cluster/bimetallic clusters toward Ullmann or Sonogashira products. Theoretical calculations support the unsaturated Cu to be the active site on the nanocluster (NC) and act like a single-atom catalyst. This highlights the effect of mono copper atom doping on the unique selectivity in the Sonogashira cross-coupling reaction.
Transformation chemistry has advanced significantly in
recent years
as an excellent methodology for synthesizing new nanoclusters and
functionalizing the existing ones. However, rational synthesis and
fundamental understanding of the structural evolution among clusters
have not yet been achieved in nanocluster science. A deeper understanding
of the fundamental aspects of structure–property correlation
is necessary for the employment of befitting nanoclusters for specific
applications. Very recently, the transformation of nanoclusters without
the use of conventional co-reactants has been brought to light. These
co-reactant-less transformations are triggered by various conditions,
such as pH, solvent, light, temperature, etc. In this perspective,
we discuss how this unique method of transformation without any co-reactant
benefits the basic understanding of growth patterns and the corresponding
property evolution in nanoclusters.
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