Dithiophosphonate-Protected Eight-Electron Superatomic Ag21 Nanocluster: Synthesis, Isomerism, Luminescence, and Catalytic Activity.

The structure-property relationship considering isomerism-tuned photoluminescence and efficient catalytic activity of silver nanoclusters (NCs) is exclusive. Asymmetrical dithiophosphonate NH4[S2P(OR)(p-C6H4OCH3)] ligated first atomically precise silver NCs [Ag21{S2P(OR)(p-C6H4OCH3)}12]PF6 {where, R = nPr (1), Et (2)} were established by single-crystal X-ray diffraction and characterized by electrospray ionization mass spectrometry, NMR (31P, 1H, 2H), X-ray photoelectron spectroscopy, UV-visible, energy-dispersive X-ray spectroscopy, Fourier transforms infrared, thermogravimetric analysis, etc. NCs 1 and 2 consist of eight silver atoms in a cubic framework and enclose an Ag@Ag12-centered icosahedron to constitute an Ag21 core of Th symmetry, which is concentrically inscribed within the S24 snub-cube, P12 cuboctahedron, and the O12 truncated tetrahedron formed by 12 dithiophosphonate ligands. These NCs facilitate to be an eight-electron superatom (1S21P6), in which eight capping Ag atoms exhibit structural isomerism with documented isoelectronic [Ag21{S2P(OiPr)2}12]PF6, 3. In contrast to 3, the stapling of dithiophosphonates in 1 and 2 triggered bluish emission within the 400 to 500 nm region at room temperature. The density functional theory study rationalized isomerization and optical properties of 1, 2, and 3. Both (1, and 2) clusters catalyzed a decarboxylative acylarylation reaction for rapid oxindole synthesis in 99% yield under ambient conditions and proposed a multistep reaction pathway. Ultimately, this study links nanostructures to their physical and catalytic properties.

A Simple Nickel Metal-Organic Framework-Catalyzed Borylation of Aryl Chlorides and Bromides.

We report a recyclable and efficient catalyst system based on a nickel-benzene tricarboxylic acid metal-organic framework (Ni-BTC MOF) for the borylation of aryl halides, including aryl chlorides, with bis(pinacolato)diboron, affording aryl boronate esters in high yields (up to >99% yield) with high selectivity. This protocol demonstrates broad functional group tolerance. Catalyst can be recyclable up to four times, and gram-scale reactions further highlights the usefulness of this method. In situ EPR experiments confirmed the formation of catalytically active Ni(I) species.

Ag-S Type Quantum Dots versus Superatom Nanocatalyst: A Single Sulfur Atom Modulated Decarboxylative Radical Cascade Reaction.

The preparation of high-nuclearity silver nanoclusters in quantitative yield remains exclusive and their potential applications in the catalysis of organic reactions are still undeveloped. Here, we have synthesized a quantum dot (QD)-based catalyst, [Ag62S13(SBut)32](PF6)4 (denoted as Ag62S12-S) in excellent yield that enables the direct synthesis of pharmaceutically precious 3,4-dihydroquinolinone in 92% via a decarboxylative radical cascade reaction of cinnamamide with α-oxocarboxylic acid under mild reaction conditions. In comparison, a superatom [Ag62S12(SBut)32](PF6)2 (denoted as Ag62S12) with identical surface anatomy and size, but without a central S2- atom in the core, gives an improved yield (95%) in a short time and exhibits higher reactivity. Multiple characterization techniques (single-crystal X-ray diffraction, nuclear magnetic resonance (1H and 31P), electrospray ionization mass spectrometry, energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis) confirm the formation of Ag62S12-S. The BET results expose the total active surface area in supporting a single e- transfer reaction mechanism. Density functional theory reveals that leaving the central S atom of Ag62S12-S leads to higher charge transfer from Ag62S12 to the reactant, accelerates the decarboxylation process, and correlates the catalytic properties with the structure of the nanocatalyst.

Facile Fabrication of Ni9 S8 /Ag2 S Intertwined Structures for Oxygen and Hydrogen Evolution Reactions.

Here, we report the fabrication of the unique intertwined Ni9 S8 /Ag2 S composite structure with hexagonal shape from their molecular precursors by one-pot thermal decomposition. Various spectroscopic and microscopic techniques were utilized to confirm the Ni9 S8 /Ag2 S intertwined structure. Powder X-ray Powder Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis suggest that there is an enrichment of Ni9 S8 phase in Ni9 S8 /Ag2 S. The presence of Ag2 S in Ni9 S8 /Ag2 S improves the conductivity by reducing the interfacial energy and charge transfer resistance. When Ni9 S8 /Ag2 S is employed as an electrocatalyst for electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity, it requires a low overpotential of 152 mV for HER and 277 mV for OER to obtain the geometrical current density of 10 mA cm-2 , which is definitely superior to that of its components Ni9 S8 and Ag2 S. This work provides a simple design route to develop an efficient and durable electrocatalyst with outstanding OER and HER performance and the present catalyst (Ni9 S8 /Ag2 S) deserves as a potential candidate in the field of energy conversion systems.

Dithiophosphonate Anchored Heterometallic (Ag(I)/Fe(II)) Molecular Catalysts for Electrochemical Hydrogen Evolution Reaction.

The dichalcogenide ligated molecules in catalysis to produce molecular hydrogen through electroreduction of water are rarely explored. Here, a series of heterometallic [Ag4(S2PFc(OR)4] [where Fc = Fe(η5-C5H4)(η5-C5H5), R = Me, 1; Et, 2; nPr, 3; isoAmyl, 4] clusters were synthesized and characterized by IR, absorption spectroscopy, NMR (1H, 31P), and electrospray ionization mass spectrometry. The molecular structures of 1, 2, and 3 clusters were established by single-crystal X-ray crystallographic analysis. The structural elucidation shows that each triangular face of a tetrahedral silver(I) core is capped by a ferrocenyl dithiophosphonate ligand in a trimetallic triconnective (η3; µ2, µ1) pattern. A comparative electrocatalytic hydrogen evolution reaction of 1-5 (R = iPr, 5) was studied in order to demonstrate the potential of these clusters in water splitting activity. The experimental results reveal that catalytic performance decreases with increases in the length of the carbon chain and branching within the alkoxy (-OR) group of these clusters. Catalytic durability was found effective even after 8 h of a chronoamperometric stability test along with 1500 cycles of linear sweep voltammetry performance, and only 15 mV overpotential was increased at 5 mA/cm2 current density for cluster 1. A catalytic mechanism was proposed by applying density functional theory (DFT) on clusters 1 and 2 as a representative. Here, a µ1 coordinated S-site between Ag4 core and ligand was found a reaction center. The experimental results are also in good accordance with the DFT analysis.

Copper hydride clusters in energy storage and conversion.

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.

Nano-Heteroarchitectures of Two-Dimensional MoS2@ One-Dimensional Brookite TiO2 Nanorods: Prominent Electron Emitters for Displays.

We report comparative field electron emission (FE) studies on a large-area array of two-dimensional MoS2-coated @ one-dimensional (1D) brookite (ß) TiO2 nanorods synthesized on Si substrate utilizing hot-filament metal vapor deposition technique and pulsed laser deposition method, independently. The 10 nm wide and 760 nm long 1D ß-TiO2 nanorods were coated with MoS2 layers of thickness ∼4 (±2), 20 (±3), and 40 (±3) nm. The turn-on field (E on) of 2.5 V/µm required to a draw current density of 10 µA/cm2 observed for MoS2-coated 1D ß-TiO2 nanorods emitters is significantly lower than that of doped/undoped 1D TiO2 nanostructures, pristine MoS2 sheets, MoS2@SnO2, and TiO2@MoS2 heterostructure-based field emitters. The orthodoxy test confirms the viability of the field emission measurements, specifically field enhancement factor (ßFE) of the MoS2@TiO2/Si emitters. The enhanced FE behavior of the MoS2@TiO2/Si emitter can be attributed to the modulation of the electronic properties due to heterostructure and interface effects, in addition to the high aspect ratio of the vertically aligned TiO2 nanorods. Furthermore, these MoS2@TiO2/Si emitters exhibit better emission stability. The results obtained herein suggest that the heteroarchitecture of MoS2@ß-TiO2 nanorods holds the potential for their applications in FE-based nanoelectronic devices such as displays and electron sources. Moreover, the strategy employed here to enhance the FE behavior via rational design of heteroarchitecture structure can be further extended to improve other functionalities of various nanomaterials.

[Ag20 {S2 P(OR)2 }12 ]: A Superatom Complex with a Chiral Metallic Core and High Potential for Isomerism.

The synthesis and structural determination of a silver nanocluster [Ag20 {S2 P(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 {S2 P(OiPr)2 }12 ](PF6 ) (1) by borohydrides. Single-crystal X-ray analysis displays an Ag20 core of pseudo C3 symmetry comprising a silver-centered Ag13 icosahedron capped by seven silver atoms. Its n-propyl derivative, [Ag20 {S2 P(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 Ag20 cores. Both Ag20 clusters 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 {S2 P(OR)2 }12 ](5-) external shell. Two additional structural variations are predicted by DFT, showing the potential for isomerism in such [Ag20 {S2 P(OR)2 }12 ] species.

Polyhydrido Copper Clusters: Synthetic Advances, Structural Diversity, and Nanocluster-to-Nanoparticle Conversion.

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 (µ2-H) and capping (µ3-H) hydride modes, followed by an interstitial (µ4-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 (µ3-H) and interstitial (µ(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.

Diselenophosphate-Induced Conversion of an Achiral [Cu20H11{S2P(OiPr)2}9] into a Chiral [Cu20H11{Se2P(OiPr)2}9] Polyhydrido Nanocluster.

A polyhydrido copper nanocluster, [Cu20H11{Se2P(OiPr)2}9] (2H), which exhibits an intrinsically chiral inorganic core of C3 symmetry, was synthesized from achiral [Cu20H11{S2P(OiPr)2}9] (1H) of C(3h) symmetry by a ligand-exchange method. The structure has a distorted cuboctahedral Cu13 core, two triangular faces of which are capped along the C3 axis, one by a Cu6 cupola and the other by a single Cu atom. The Cu20 framework is further stabilized by 9 diselenophosphate and 11 hydride ligands. The number of hydride, phosphorus, and selenium resonances and their splitting patterns in multinuclear NMR spectra of 2H indicate that the chiral Cu20H11 core retains its C3 symmetry in solution. The 11 hydride ligands were located by neutron diffraction experiments and shown to be capping µ3-H and interstitial µ5-H ligands (in square-pyramidal and trigonal-bipyramidal cavities), as supported by DFT calculations on [Cu20H11(Se2PH2)9] (2H') as a simplified model.

[Cu32 (H)20 {S2 P(OiPr)2 }12 ]: The Largest Number of Hydrides Recorded in a Molecular Nanocluster by Neutron Diffraction.

An air- and moisture-stable nanoscale polyhydrido copper cluster [Cu32 (H)20 {S2 P(OiPr)2 }12 ] (1H ) was synthesized and structurally characterized. The molecular structure of 1H exhibits a hexacapped pseudo-rhombohedral core of 14 Cu atoms sandwiched between two nestlike triangular cupola fragments of (2×9) Cu atoms in an elongated triangular gyrobicupola polyhedron. The discrete Cu32 cluster is stabilized by 12 dithiophosphate ligands and a record number of 20 hydride ligands, which were found by high-resolution neutron diffraction to exhibit tri-, tetra-, and pentacoordinated hydrides in capping and interstitial modes. This result was further supported by a density functional theory investigation on the simplified model [Cu32 (H)20 (S2 PH2 )12 ].

Copper(I) diselenocarbamate clusters: synthesis, structures and single-source precursors for Cu and Se composite materials.

Neutral tetrahedral [Cu4(Se2CNnPr2)4] (1), monocationic hydride-centered tetracapped tetrahedral [Cu8(H){Se2CNR2}6]+ (R = nPr, 2H; Et, 3H) and neutral hydride-centered tricapped tetrahedral [Cu7(H){Se2CNR2}6] (R = nPr, 4H; Et, 5H) clusters were formed. They are the first Cu(I) complexes supported by dialkyl diselenocarbamates. The as-synthesized complexes 2H and 3H, formed from a reaction mixture of Cu(I) salts, diselenocarbamates, and [BH4]− in an 8:6:1 ratio, can be further reduced to 4H and 5H, respectively, in the presence of one equiv. of [BH4]−. Replacement of [BH4]− with [BD4]− afforded the deuteride analogues [Cu8(D){Se2CNR2}6]+ (R = nPr, 2D; Et, 3D) and [Cu7(D){Se2CNR2}6] (R = nPr, 4D; Et, 5D), which confirm the presence of hydride in the corresponding (2H, 3H, 4H and 5H) compounds. These complexes were fully characterized by elemental analysis, ESI-MS, and 1H, 2H and 77Se NMR spectroscopy, and their molecular structures were unequivocally established by single crystal X-ray crystallographic analyses (1, 2H­5H). The hydride-encapsulated copper frameworks of (2H, 3H) and (4H, 5H) reveal a tetracapped tetrahedral cage of Cu8 and a tricapped tetrahedral cage of Cu7, respectively, which are enclosed within a Se12 icosahedron constituted by six dialkyl diselenocarbamate ligands. Compounds 2H and 3H display orange emission in both the solid and solution state under UV irradiation at 77 K. In addition, the thermolysis behaviors of 2H were studied to demonstrate the potential of these compounds as single-source precursors for copper selenide nanocomposites, which were analyzed by XRD, EDX, and SEM techniques.

[Ag21{S2P(OiPr)2}12]+: an eight-electron superatom.

A novel discrete [Ag21{S2P(OiPr)2}12](PF6) nanocluster has been synthesized and characterized by single-crystal X-ray diffraction and also NMR spectroscopy ((1)H, (31)P), ESI mass spectrometry, and other analytic techniques (XPS, EDS, UV/Vis spectroscopy). The Ag21 skeleton has an unprecedented silver-centered icosahedron that is capped by eight additional metal atoms. The whole framework is protected by twelve dithiophosphate ligands. According to the spherical Jellium model, the stability of monocationic nanocluster can be described by an 8-electron superatom with 1S(2) 1P(6) configuration, as confirmed by DFT calculations.

Chinese puzzle molecule: a 15†hydride, 28†copper atom nanoball.

The syntheses of the first rhombicuboctahedral copper polyhydride complexes [Cu28 (H)15 (S2 CNR)12 ]PF6 (NR=N(n) Pr2 or aza-15-crown-5) are reported. These complexes were analyzed by single-crystal X-ray and one by neutron diffraction. The core of each copper hydride nanoparticle comprises one central interstitial hydride and eight outer-triangular-face-capping hydrides. A further six face-truncating hydrides form an unprecedented bridge between the inner and outer copper atom arrays. The irregular inner Cu4 tetrahedron is encapsulated within the Cu24 rhombicuboctahedral cage, which is further enclosed by an array of twelve dithiocarbamate ligands that subtends the truncated octahedron of 24 sulfur atoms, which is concentric with the Cu24 rhombicuboctahedron and Cu4 tetrahedron about the innermost hydride. For these compounds, an intriguing, albeit limited, H2 evolution was observed at room temperature, which is accompanied by formation of the known ion [Cu8 (H)(S2 CNR)6 ](+) upon exposure of solutions to sunlight, under mild thermolytic conditions, and on reaction with weak (or strong) acids.

A nanospheric polyhydrido copper cluster of elongated triangular orthobicupola array: liberation of H2 from solar energy.

An unprecedented air-stable, nanospheric polyhydrido copper cluster, [Cu20H11(S2P(O(i)Pr)2)9] (1H), which is the first example of an elongated triangular orthobicupola array of Cu atoms having C3h symmetry, was synthesized and characterized. Its composition was primarily determined by electrospray ionization mass spectrometry, and it was fully characterized by (1)H, (2)H, and (31)P NMR spectroscopy and single-crystal X-ray diffraction (XRD). The structure of complex 1H can be expressed in terms of a trigonal-bipyramidal [Cu2H5](3-) unit anchored within an elongated triangular orthobicupola containing 18 Cu atoms, which is further stabilized by 18 S atoms from nine dithiophosphate ligands and six capping hydrides. The positions of the 11 hydrides revealed by low temperature XRD were supported by a density functional theory investigation on the simplified model [Cu20H11(S2PH2)9] with C3h symmetry. 1H is capable of releasing H2 gas upon irradiation with sunlight, under mild thermal conditions (65 °C), or in the presence of acids at room temperature.

Vertex-fused metallaborane clusters: synthesis, characterization and electronic structure of [(eta5-C5Me5Mo)3MoB9H18].

The reaction of the [(eta(5)-C(5)Me(5))MoCl(4)] complex with [LiBH(4).THF] in toluene at -70 degrees C, followed by pyrolysis at 110 degrees C, afforded dark brown [(eta(5)-C(5)Me(5)Mo)(3)MoB(9)H(18)], 2, in parallel with the known [(eta(5)-C(5)Me(5)Mo)(2)B(5)H(9)], 1. Compound 2 has been characterized in solution by (1)H, (11)B, and (13)C NMR spectroscopy and elemental analysis, and the structural types were unequivocally established by crystallographic studies. The title compound represents a novel class of vertex-fused clusters in which a Mo atom has been fused in a perpendicular fashion between two molybdaborane clusters. Electronic structure calculations employing density functional theory yield geometries in agreement with the structure determinations, and on grounds of density functional theory calculations, we have analyzed the bonding patterns in the structure.

Chlorinated hypoelectronic dimetallaborane clusters: synthesis, characterization, and electronic structures of (eta(5)-C5Me5W)2B5H(n)Cl(m) (n = 7, m = 2 and n = 8, m = 1).

Pyrolysis of (eta(5)-C(5)Me(5)WH(3))B(4)H(8), 1, in the presence of excess BHCl(2) x SMe(2) in toluene at 100 degrees C led to the isolation of (eta(5)-C(5)Me(5)W)(2)B(5)H(9), 2, and B-Cl inserted (eta(5)-C(5)Me(5)W)(2)B(5)H(8)Cl, 3, and (eta(5)-C(5)Me(5)W)(2)B(5)H(7)Cl(2), 4-7 (four isomers). All the chlorinated tungstaboranes were isolated as red and air and moisture sensitive solids. These new compounds have been characterized in solution by (1)H, (11)B, (13)C NMR, and the structural types were unequivocally established by crystallographic analysis of compounds 3, 4, and 7. Density functional theory (DFT) calculations were carried out on the model molecules of 3-7 to elucidate the actual electronic structures of these chlorinated species. On grounds of DFT calculations we demonstrated the role of transition metals, bridging hydrogens, and the effect of electrophilic substitution of hydrogens at B-H vertices of metallaborane structures.