Organic ligands that
protect the surfaces of clusters and nanoparticles
against reactions and control the rate of growth are generally considered
to be inert passive coatings. Here, we demonstrate in a computational
study that ligands can also strongly affect redox properties of clusters.
Attaching phosphine ligands to simple metal, noble metal, semiconducting,
metal-oxide, and metal-chalcogen clusters is shown to severely reduce
ionization energies in all classes of clusters. Several of the simple
and noble metal-ligated clusters are transformed into super donors
with ionization energies nearly half that of cesium atoms and extremely
low second and third ionization energies. The reduction in ionization
energy can be split into initial and final state effects. The initial
state effect derives in part from the surface dipole but primarily
through the formation of bonding/antibonding orbitals that shifts
the highest occupied molecular orbital. The final state effect derives
from the enhanced binding of the donor ligand to the charged cluster.
In comparing simple and noble-metal clusters with transition-metal
clusters, the strength of the different mechanisms changes in that
the initial state effect is smaller in transition-metal clusters,
and the final state effect plays a larger role. Ligation is shown
to be an outstanding strategy for the formation of multiple electron
donors.
We report the synthesis, crystal structure, and electronic structure calculations of a one-dimensional silver-thiolate cluster-assembled and its ultrafast spectroscopic investigation. Experiments and theory find the material to have a significant gap as the HOMO−LUMO absorption corresponds to 2.69 eV, and the defect-free structure is calculated to have a gap of 2.82 eV. Cluster models demonstrate that the gap energy is lengthdependent. Theoretical studies identify a nonbonding metallophilic interaction that exists between two Ag atoms in adjacent strings that helps to stabilize the chain structure. Transient absorption spectroscopy reveals that the electron dynamics is a mixture of the behavior of cluster and nanoparticle, with the material having a 346 fs ground-state relaxation like a cluster, and the electron dynamics is dominated by electron−phonon coupling with a decay time of 1.5 ps, unlike the isolated cluster whose decay is mostly radiative.
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