Browsing by Author "Liu, C.W."

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[Ag20{S2P(OR)2}12]: A Superatom Complex with a Chiral Metallic Core and High Potential for Isomerism
(Wiley-VCH Verlag, 2016) Dhayal, R.S.; Lin, Y.-R.; Liao, J.-H.; Chen, Y.-J.; Liu, Y.-C.; Chiang, M.-H.; Kahlal, S.; Saillard, J.-Y.; Liu, C.W.
The synthesis and structural determination of a silver nanocluster [Ag20{S2P(OiPr)2}12] (2), which contains an intrinsic chiral metallic core, is produced by reduction of one silver ion from the eight-electron superatom complex [Ag21{S2P(OiPr)2}12](PF6) (1) by borohydrides. Single-crystal X-ray analysis displays an Ag20core of pseudo C3symmetry comprising a silver-centered Ag13icosahedron capped by seven silver atoms. Its n-propyl derivative, [Ag20{S2P(OnPr)2}12] (3), can also be prepared by the treatment of silver(I) salts and dithiophosphates in a stoichiometric ratio in the presence of excess amount of [BH4]?. Crystal structure analyses reveal that the capping silver-atom positions relative to their icosahedral core are distinctly different in 2 and 3 and generate isomeric, chiral Ag20cores. Both Ag20clusters display an emission maximum in the near IR region. DFT calculations are consistent with a description within the superatom model of an 8-electron [Ag13]5+core protected by a [Ag7{S2P(OR)2}12]5?external shell. Two additional structural variations are predicted by DFT, showing the potential for isomerism in such [Ag20{S2P(OR)2}12] species. ? 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Copper hydride clusters in energy storage and conversion
(Royal Society of Chemistry, 2019) Dhayal, R.S; Van Zyl ,W.E; Liu, C.W.
Hydrogen is seen as an increasingly important clean and sustainable energy source going into the future. There are a host of materials being investigated for the storage of hydrogen. In this frontier, we provide an overview of hydride clusters derived from Earth-abundant copper being used for the storage and conversion of hydrides into hydrogen, and the reaction of CO2 with hydride sources to produce the formic acid/formate pairing, which are considered excellent hydrogen carriers. We summarize the main synthesis methods to stabilize high-nuclearity hydride clusters with phosphine, N-heterocyclic carbene, and in particular phosphor-1,1-dithiolate ligands. Unprecedented structures and hydride geometries have been revealed through both X-ray and neutron single crystal analyses. We point to the release of hydrogen in such hydride clusters through solar irradiation, thermolysis and acid treatments. Finally, we show the facile formation of rhombic nanoparticle copper morphologies derived from accurately determined high-nuclearity clusters and suggest that this could provide a mechanism that links molecular structures with bulk microstructures of materials. © 2019 The Royal Society of Chemistry.
Polyhydrido Copper Clusters: Synthetic Advances, Structural Diversity, and Nanocluster-to-Nanoparticle Conversion
(American Chemical Society, 2016) Dhyal, Rajendra S; Zyl, Werner E. van; Liu, C. W.; Dhayal, R.S.; Van Zyl, W.E.; Liu, C.W.
Conspectus: Metal hydride clusters have historically been studied to unravel their aesthetically pleasing molecular structures and interesting properties, especially toward hydrogen related applications. Central to this work is the hydride ligand, H?, the smallest closed-shell spherical anion known. Two new developments in polyhydrido nanocluster chemistry include the determination of heretofore unknown hydride coordination modes and novel structural constructs, and conversion from the molecular entities to rhombus-shaped copper nanoparticles (CuNPs). These advances, together with hydrogen evolution and catalysis, have provided both experimentalists and theorists with a rich scientific directive to further explore. The isolation of hexameric [{(Ph3P)CuH}6] (Stryker reagent) could be regarded as the springboard for the recent emergence of polyhydrido copper cluster chemistry due to its utilization in a variety of organic chemical transformations. The stability of clusters of various nuclearity was improved through phosphine, pyridine, and carbene type ligands. Our focus lies with the isolation of novel copper (poly)hydride clusters using mostly the phosphor-1,1-dithiolato type ligands. We found such chalcogen-stabilized clusters to be exceptionally air and moisture stable over a wide range of nuclearities (Cu7 to Cu32). In this Account, we (i) report on state-of-the-art copper hydride cluster chemistry, especially with regards to the diverse and novel structural types generally, and newly discovered hydride coordination modes in particular, (ii) demonstrate the indispensable power of neutron diffraction for the unambiguous assignment and location of hydride ligand(s) within a cluster, and (iii) prove unique transformations that can occur not only between well characterized high nuclearity clusters, but also how such clusters can transform to uniquely shaped nanoparticles of several nanometers in diameter through copper hydride reduction.The increase in the number of low- to high-nuclearity hydride clusters allows for different means by which they can be classified. We chose a classification based on the coordination mode of hydride ligand within the cluster. This includes copper clusters associated with bridging (?2-H) and capping (?3-H) hydride modes, followed by an interstitial (?4-H) hydride mode that was introduced for the first time into octa- and hepta-nuclear copper clusters stabilized by dichalcogen-type ligands. This breakthrough provided a means to explore higher nuclearity polyhydrido nanoclusters, which contain both capping (?3-H) and interstitial (?(4-6)-H) hydrides. The presence of bidentate ligands having mixed S/P dative sites led to air- and moisture-stable copper hydride nanoclusters. The formation of rhombus-shaped nanoparticles (CuNPs) from copper polyhydrides in the presence of excess borohydrides suggests the presence of metal hydrides as intermediates during the formation of nanoparticles. ? 2015 American Chemical Society.
Synthesis, Structural Characterization, and H2 Evolution Study of a Spheroid-Shape Hydride-Rich Copper Nanocluster
(Wiley-Blackwell, 2018) Dhayal, R.S.; Chen, H.-P.; Liao, J.-H.; van Zyl, W.E.; Liu, C.W.
This study reports on new bis-2-butyl dithiophosphate-stabilized polyhydrido copper nanoclusters, [Cu32(H)20{S2P(O2Bu)2}12], 1H, and [Cu20H11{S2P(O2Bu)2}9], 2H. The clusters 1H and 2H have been characterized by a variety of techniques including multinuclear NMR (1H, 2H, 31P), electrospray ionization mass spectrometry (ESI-MS), and low temperature X-ray crystallography. The presence of hydride ligands was supported by the 2H NMR spectrum of the deuteride analogs [Cu32(D)20{S2P(O2Bu)2)12], 1D and [Cu20D11{S2P(O2Bu)2}9], 2D. The metal skeleton of 1H revealed that a hexacapped rhombohedron of fourteen copper atoms was sandwiched between two sets of eighteen (9x2) copper atoms in a cup shape and the entire cluster is an elongated triangular gyrobicupola. The metal core is stabilized by 20 hydride ligands via various (?3, ?4, ?5)-H coordination modes and 12 dithiophosphate ligands coordinated either in tetrametallic tetraconnective (?4: ?2, ?2) or trimetallic tetraconnective (?3: ?2, ?2) patterns. The structural motif of 2H showed fascinating correlations with 1H having an elongated triangular orthobicupola framework of eighteen (9x2) copper atoms with an encapsulated linear Cu2 unit along the C3 axis and protected by 11 (?3, ?4)-H and 9 dithiophosphate ligands in a tetrametallic tetraconnective (?4: ?2, ?2) mode. The isopropyl derivatives, [Cu32(H)20{S2P(OiPr)2}12], 3H and [Cu20(H)11{S2P(OiPr)2}9], 4H, were used to study H2 evolution under different physico-chemical conditions and proved to be excellent models for hydrogen storage materials. Additionally, following H2 evolution under sunlight irradiation, mild thermolysis (?60 oC) and acidification, cluster 3H converted into [Cu8(H){S2P(OiPr)2}6]+, 5H. Intriguingly 5H can react with Cu+ salt in the presence of [BH4]? and re-form 3H. Cluster 4H also reproducibly re-formed via the reaction between 5H and [BH4]? from which a continuous cycle of cluster conversion and H2 evolution is proposed. Rhombus-shaped copper nanoparticles fabricated from further reductions of 3H and 4H showed the intermediary role of metal hydrides in the formation of metal nanoparticles under wet chemical methods. ? 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim