Mohammad J. Alhilaly

Copper-based nanomaterials have attracted tremendous interest due to their unique properties in the fields of photoluminescence and catalysis. As a result, studies on the correlation between their molecular structure and their properties are of great importance. Copper nanoclusters are a new class of nanomaterials that can provide an atomic-level view of the crystal structure of copper nanoparticles. Herein, a high-nuclearity copper nanocluster with 81 copper atoms, formulated as [Cu81(PhS)46(tBuNH2)10(H)32]3+ (Cu81), was successfully synthesized and fully studied by X-ray crystallography, X-ray photoelectron spectroscopy, hydrogen evolution experiments, electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and density functional theory calculations. Cu81 exhibits extraordinary structural characteristics, including (i) three types of novel epitaxial surface-protecting motifs; (ii) an unusual planar Cu17 core; (iii) a hemispherical shell, comprised of a curved surface layer and a planar surface layer; and (iv) two distinct, self-organized arrangements of protective ligands on the curved and planar surfaces. The present study sheds light on structurally unexplored copper nanomaterials and paves the way for the synthesis of high-nuclearity copper nanoclusters.

Here, we demonstrate an approach for synthesizing and structurally characterizing three atomically precise anion-templated silver thiolate nanoclusters, two of which form one- and two-dimensional structural frameworks composed of bipyridine-linked nanocluster nodes (referred to as nanocluster-based frameworks, NCFs). We describe the critical role of the chloride (Cl-) template in controlling the nanocluster’s nuclearity with atomic precision; and the effect of a single Ag atom difference in the nanocluster’s size in controlling the NCF dimensionality, modulating the optical properties, and improving the thermal stability. With atomically precise assembly and size control, nanoclusters could be widely adopted as building blocks for the construction of tunable cluster-based framework materials.

Engineering the surface ligands of metal nanoparticles is critical in designing unique arrangements of metal atoms. Here, we report the synthesis and total structure determination of a large box-shaped Ag₆₇ nanocluster (NC) protected by a mixed shell of thiolate (2,4-dimethylbenzenethiolate, SPhMe₂) and phosphine (triphenylphosphine, PPh₃) ligands. Single crystal X-ray diffraction (SCXRD) and electrospray ionization mass spectrometry (ESI-MS) revealed the cluster formula to be [Ag₆₇(SPhMe₂)₃₂(PPh₃)₈]³⁺. The crystal structure shows an Ag₂₃ metal core covered by a layer of Ag₄₄S₃₂P₈ arranged in the shape of a box. The Ag₂₃ core was formed through an unprecedented centered cuboctahedron, i.e., Ag₁₃, unlike the common centered Ag₁₃ icosahedron geometry. Two types of ligand motifs, eight AgS₃P and eight bridging thiols, were found to stabilize the whole cluster. The optical spectrum of this NC displayed highly structured multiple absorption peaks. The electronic structure and optical spectrum of Ag₆₇ were computed using time-dependent density functional theory (TDDFT) for both the full cluster [Ag₆₇(SPhMe₂)₃₂(PPh₃)₈]³⁺ and a reduced model [Ag₆₇(SH)₃₂(PH₃)₈]³⁺. The lowest metal-to-metal transitions in the range 500–800 nm could be explained by considering the reduced model that shows almost identical electronic states to 32 free electrons in a jellium box. The successful synthesis of the large box-shaped Ag₆₇ NC facilitated by the combined use of phosphine and thiol paves the way for synthesizing other metal clusters with unprecedented shapes by judicious choice of thiols and phosphines.

Silver nanoparticles with an atomically precise molecular formula [Ag₂₅(SR)₁₈]⁻ (−SR: thiolate) are synthesized, and their single-crystal structure is determined. This synthesized nanocluster is the only silver nanoparticle that has a virtually identical analogue in gold, i.e., [Au₂₅(SR)₁₈]⁻, in terms of number of metal atoms, ligand count, superatom electronic configuration, and atomic arrangement. Furthermore, both [Ag₂₅(SR)₁₈]⁻ and its gold analogue share a number of features in their optical absorption spectra. This unprecedented molecular analogue in silver to mimic gold offers the first model nanoparticle platform to investigate the centuries-old problem of understanding the fundamental differences between silver and gold in terms of nobility, catalytic activity, and optical property.