Conspectus
The past decades have witnessed
great advances in the synthesis,
structure determination, and properties investigation of coinage metal
nanoclusters. These monodisperse clusters have well-defined molecular
structures, which is advantageous in correlating structures and properties.
Metal nanoclusters are large molecules consisting of many components,
so it is a big challenge to prepare them in a rational way. Strenuous
efforts have been made to control their geometric and electronic
structures, in order to optimize their various properties.
A
metal nanocluster normally contains a metal core and a peripheral
ligand shell. The ligands do not only function as simple stabilizing
agents. It has been revealed that these ligands are able to influence
the formation processes of the nanoclusters, and they may also dictate
the sizes, shapes, and properties of nanoclusters. There are mainly
three types of ligands that are widely used as surface anchors on
coinage metal nanoclusters: thiolates, phosphines, and halides. Recent
ligand engineering has extended the scope to alkynyl ligands. As alkynyl
ligands are versatile in interacting with metal atoms, interesting
alkynyl–metal interfacial structures including linear, L-shaped,
and V-shaped staple motifs can be generated, as well as a series of
novel coinage metal nanoclusters that exhibit intriguing molecular
geometries.
The staple motifs do not simply resemble the surface
structures
of thiolate-protected nanoclusters, because the incorporation of alkynyl
ligands may significantly alter diverse properties of nanoclusters.
Compared with thiolate-protected gold nanoclusters, alkynyl-protected
ones with identical metal cores exhibit distinctly different absorption
profiles and show much improved catalytic activities for semihydrogenation
of alkynes. In addition, the participation of alkynyl ligands could
profoundly affect the luminescent properties of nanoclusters. These
“ligand effects” are mainly attributed to the different
nature of alkynyl ligands, as electronic perturbation through π-conjugated
units may largely modulate the electronic structure of the whole cluster.
In this Account, we describe the development of coinage metal nanoclusters
protected with alkynyl ligands. We will first briefly bring up the
emergence of alkynyl ligands as anchoring groups on the surfaces of
nanoclusters. Then we present the direct reduction method for the
synthesis of the following four categories of nanoclusters: (a) gold
nanoclusters with mixed-ligand shells, (b) all alkynyl-protected gold
nanoclusters, (c) heterobimetallic gold nanoclusters, and (d) silver
nanoclusters. Their molecular structures are described, and their
various alkynyl–metal interfacial structures are compared with
thiolate–metal staples. Finally, ligand effects on the properties
of the clusters, including optical absorption, luminescence, and catalysis,
are discussed. The alkynyl ligands play an important role in terms
of both structural and property aspects. We believe this Account will
attract increasing at...
