Ag₁₃-Centered Cuboctahedral Architecture in Inorganic Cluster Chemistry: A DFT Investigation

The bonding in the [Ag₁₃{μ₃-Fe­(CO)₄}₈]^3‑/5‑ clusters, which exhibit an Ag₁₃-centered cuboctahedral core, has been analyzed and rationalized by DFT calculations. Not considering the interaction with its encapsulated atom, the empty [Ag₁₂{μ₃-Fe­(CO)₄}₈]^4– cage can be considered as the assembly of 12 linearly coordinated 14-electron Ag^I metal centers. Adding a supplementary Ag⁺ at the center allows some covalent delocalized bonding which to some extent tends to reduce the electron deficiency of the 14-electron centers. Adding now two electrons strengthens the delocalized bonding between the encapsulated atom and its host, making [Ag₁₃{μ₃-Fe­(CO)₄}₈]^5– a superatom with two jellium (5s-type) electrons. TDDFT calculations predict near-IR absorption for this penta-anion, because of the presence of an a_1g HOMO in the middle of an energy gap. Luminescence in the same optical range is also suggested. Other related cubococtahedral species, such as [Ag₂₃(SH)₁₆]⁻, a model for the known 8-electron [Au₂₃(SR)₁₆]⁻ species which exhibits a bicapped centered dodecahedral kernel structure, have also been investigated

Ag₁₃-Centered Cuboctahedral Architecture in Inorganic Cluster Chemistry: A DFT Investigation

The bonding in the [Ag₁₃{μ₃-Fe­(CO)₄}₈]^3‑/5‑ clusters, which exhibit an Ag₁₃-centered cuboctahedral core, has been analyzed and rationalized by DFT calculations. Not considering the interaction with its encapsulated atom, the empty [Ag₁₂{μ₃-Fe­(CO)₄}₈]^4– cage can be considered as the assembly of 12 linearly coordinated 14-electron Ag^I metal centers. Adding a supplementary Ag⁺ at the center allows some covalent delocalized bonding which to some extent tends to reduce the electron deficiency of the 14-electron centers. Adding now two electrons strengthens the delocalized bonding between the encapsulated atom and its host, making [Ag₁₃{μ₃-Fe­(CO)₄}₈]^5– a superatom with two jellium (5s-type) electrons. TDDFT calculations predict near-IR absorption for this penta-anion, because of the presence of an a_1g HOMO in the middle of an energy gap. Luminescence in the same optical range is also suggested. Other related cubococtahedral species, such as [Ag₂₃(SH)₁₆]⁻, a model for the known 8-electron [Au₂₃(SR)₁₆]⁻ species which exhibits a bicapped centered dodecahedral kernel structure, have also been investigated

Neutron Diffraction Studies of a Four-Coordinated Hydride in Near Square-Planar Geometry

The structure of a nanospheric polyhydrido copper cluster, [Cu₂₀(H)₁₁{S₂P­(O^<i>i</i>Pr)₂}₉], was determined by single-crystal neutron diffraction. The Cu₂₀ cluster consists of an elongated triangular orthobicupola constructed from 18 Cu atoms that encapsulate a [Cu₂H₅]^3– ion with an exceptionally short Cu–Cu distance. The 11 hydrides in the cluster display three different coordination modes to the Cu atoms: six μ₃-hydrides in a pyramidal geometry, two μ₄-hydrides in a tetrahedral cavity, and three μ₄-hydrides in an unprecedented near square-planar geometry. The neutron data set was collected for 7 days on a small crystal with dimensions of 0.20 mm × 0.50 mm × 0.65 mm using the Spallation Neutron Source TOPAZ single-crystal time-of-flight Laue diffractometer at Oak Ridge National Laboratory. The final <i>R</i>-factor was 8.63% for 16,014 reflections

Neutron Diffraction Studies of a Four-Coordinated Hydride in Near Square-Planar Geometry

The structure of a nanospheric polyhydrido copper cluster, [Cu₂₀(H)₁₁{S₂P­(O^<i>i</i>Pr)₂}₉], was determined by single-crystal neutron diffraction. The Cu₂₀ cluster consists of an elongated triangular orthobicupola constructed from 18 Cu atoms that encapsulate a [Cu₂H₅]^3– ion with an exceptionally short Cu–Cu distance. The 11 hydrides in the cluster display three different coordination modes to the Cu atoms: six μ₃-hydrides in a pyramidal geometry, two μ₄-hydrides in a tetrahedral cavity, and three μ₄-hydrides in an unprecedented near square-planar geometry. The neutron data set was collected for 7 days on a small crystal with dimensions of 0.20 mm × 0.50 mm × 0.65 mm using the Spallation Neutron Source TOPAZ single-crystal time-of-flight Laue diffractometer at Oak Ridge National Laboratory. The final <i>R</i>-factor was 8.63% for 16,014 reflections

A Twelve-Coordinated Iodide in a Cuboctahedral Silver(I) Skeleton

Three new halide-centered octanuclear silver­(I) complexes, [Ag₈(X)­{S₂P­(CH₂CH₂Ph)₂}₆]­(PF₆), X = F^–, <b>1</b>; Cl^–, <b>2</b>; Br^–, <b>3</b>; were prepared in the presence of the corresponding halide anions with silver­(I) salts and dithiophosphinate ligands. Structure analyses displayed that a Ag₈ cubic core can be modulated by the size effect of the central halide; however, an iodide-centered Ag₈ cluster was not found under similar reaction conditions. Interestingly, a luminescent dodecanuclear silver­(I) cluster, [Ag₁₂(μ₁₂-I)­(μ₃-I)₄{S₂P­(CH₂CH₂Ph)₂}₆]­(I), <b>4</b>; was then synthesized. The structure of <b>4</b> contains a novel μ₁₂-I at the center of a cuboctahedral silver­(I) atom cage, which is further stabilized by four additional μ₃-I and six dithiophosphinate ligands. To the best of our knowledge, the μ₁₂-I revealed in <b>4</b> is the highest coordination number for a halide ion authenticated by both experimental and computational studies. Previously, the μ₁₂-I was only observed in [PyH]­[{TpMo­(μ₃-S)₄Cu₃}₄(μ₁₂-I)]. The synthetic details, spectroscopic studies including multinuclear NMR and ESI-MS, structure elucidations by single crystal X-ray diffraction, and photoluminescence of <b>4</b> are reported herein

[Ag₇(H){E₂P(OR)₂}₆] (E = Se, S): Precursors for the Fabrication of Silver Nanoparticles

Reactions of Ag­(I) salt, NH₄(E₂P­(OR)₂) (R = ⁱPr, Et; E = Se, S), and NaBH₄ in a 7:6:1 ratio in CH₂Cl₂ at room temperature, led to the formation of hydride-centered heptanuclear silver clusters, [Ag₇(H)­{E₂P­(OR)₂}₆] (R = ⁱPr, E = Se (<b>3</b>): R = Et; E = S­(<b>4</b>). The reaction of [Ag₁₀(E)­{E₂P­(OR)₂}₈] with NaBH₄ in CH₂Cl₂ produced [Ag₈(H)­{E₂P­(OR)₂}₆]­(PF₆) (R = ⁱPr, E = Se (<b>1</b>): R = Et; E = S­(<b>2</b>)), which can be converted to clusters <b>3</b> and <b>4</b>, respectively, via the addition of 1 equiv of borohydride. Intriguingly clusters <b>1</b> and <b>2</b> can be regenerated via adding 1 equiv of Ag­(CH₃CN)₄PF₆ to the solution of compounds <b>3</b> and <b>4</b>, respectively. All complexes have been fully characterized by NMR (¹H, ⁷⁷Se, ¹⁰⁹Ag) spectroscopy, UV–vis, electrospray ionization mass spectrometry (ESI-MS), FT-IR, thermogravimetric analysis (TGA), and elemental analysis, and molecular structures of <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> were clearly established by single crystal X-ray diffraction. Both <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> exhibit a tricapped tetrahedral Ag₇ skeleton, which is inscribed within an E₁₂ icosahedron constituted by six dialkyl dichalcogenophosphate ligands in a tetrametallic-tetraconnective (μ₂, μ₂) bonding mode. Density functional theory (DFT) calculations on the models [Ag₇(H)­(E₂PH₂)₆] (E = Se: <b>3′</b>; E = S: <b>4′</b>) yielded to a tricapped, slightly elongated tetrahedral silver skeleton, and time-dependent DFT (TDDFT) calculations reproduce satisfyingly the UV–vis spectrum with computed transitions at 452 and 423 nm for <b>3′</b> and 378 nm for <b>4′</b>. Intriguingly further reactions of [Ag₇(H)­{E₂P­(OR)₂}₆] with 8-fold excess amounts of NaBH₄ produced monodisperse silver nanoparticles with an averaged particle size of 30 nm, which are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and UV–vis absorption spectrum

Hydrido Copper Clusters Supported by Dithiocarbamates: Oxidative Hydride Removal and Neutron Diffraction Analysis of [Cu₇(H){S₂C(aza-15-crown-5)}₆]

Reactions of Cu­(I) salts with Na­(S₂CR) (R = N^<i>n</i>Pr₂, NEt₂, aza-15-crown-5), and (Bu₄N)­(BH₄) in an 8:6:1 ratio in CH₃CN solution at room temperature yield the monocationic hydride-centered octanuclear Cu^I clusters, [Cu₈(H)­{S₂CR}₆]­(PF₆) (R = N^<i>n</i>Pr₂, <b>1</b>_<b>H</b>; NEt₂, <b>2</b>_<b>H</b>; aza-15-crown-5, <b>3</b>_<b>H</b>). Further reactions of [Cu₈(H)­{S₂CR}₆]­(PF₆) with 1 equiv of (Bu₄N)­(BH₄) produced neutral heptanuclear copper clusters, [Cu₇(H)­{S₂CR}₆] (R = N^<i>n</i>Pr₂, <b>4</b>_<b>H</b>; NEt₂, <b>5</b>_<b>H</b>; aza-15-crown-5, <b>6</b>_<b>H</b>) and clusters <b>4</b>–<b>6</b> can also be generated from the reaction of Cu­(BF₄)₂, Na­(S₂CR), and (Bu₄N)­(BH₄) in a 7:6:8 molar ratio in CH₃CN. Reformation of cationic Cu^I₈ clusters by adding 1 equiv of Cu^I salt to the neutral Cu₇ clusters in solution is observed. Intriguingly, the central hydride in [Cu₈(H)­{S₂CN^<i>n</i>Pr₂}₆]­(PF₆) can be oxidatively removed as H₂ by Ce­(NO₃)₆^2– to yield [Cu^II(S₂CN^<i>n</i>Pr₂)₂] exploiting the redox-tolerant nature of dithiocarbamates. Regeneration of hydride-centered octanuclear copper clusters from the [Cu^II(S₂CN^<i>n</i>Pr₂)₂] can be achieved by reaction with Cu­(I) ions and borohydride. The hydride release and regeneration of Cu^I₈ was monitored by UV–visible titration experiments. To our knowledge, this is the first time that hydride encapsulated within a copper cluster can be released as H₂ via chemical means. All complexes have been fully characterized by ¹H NMR, FT-IR, UV–vis, and elemental analysis, and molecular structures of <b>1</b>_<b>H</b>, <b>2</b>_<b>H</b>, and <b>6</b>_<b>H</b> were clearly established by single-crystal X-ray diffraction. Both <b>1</b>_<b>H</b> and <b>2</b>_<b>H</b> exhibit a tetracapped tetrahedral Cu₈ skeleton, which is inscribed within a S₁₂ icosahedron constituted by six dialkyl dithiocarbamate ligands in a tetrametallic-tetraconnective (μ₂, μ₂) bonding mode. The copper framework of <b>6</b>_<b>H</b> is a tricapped distorted tetrahedron in which the four-coordinate hydride is demonstrated to occupy the central site by single crystal neutron diffraction. Compounds <b>1</b>–<b>3</b> exhibit a yellow emission in both the solid state and in solution under UV irradiation at 77 K, and the structureless emission is assigned as a ³metal to ligand charge transfer (MLCT) excited state. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on model compounds match the experimental structures and provide rationalization of their bonding and optical properties

Ferrocene-Functionalized Cu(I)/Ag(I) Dithiocarbamate Clusters

A series of compounds, namely, [Cu₈(μ₄-H)­{S₂CN­MeCH₂Fc}₆]­(PF₆) (<b>1</b>), [Cu₇(μ₄-H) {S₂CN^<i>i</i>PrCH₂Fc}₆] (<b>2</b>), [Cu₃{S₂CN­(Bz) (CH₂Fc)}₂(dppf)₂]­(PF₆) (<b>3</b>), and [Ag₂{S₂CNMe­(CH₂Fc)}₂(PPh₃)₂] (<b>4</b>) (dppf = 1,1′-bis­(diphenylphosphino)­ferrocene), supported by multiferrocene assemblies, were synthesized. All the compounds were characterized by ¹H NMR, Fourier transform infrared, elemental analysis, and electrospray ionization mass spectrometry techniques. Single-crystal X-ray structural analysis revealed that <b>1</b> is a monocationic octanuclear Cu^I cluster and that <b>2</b> is a neutral heptanuclear Cu^I cluster with tetracapped tetrahedral (<b>1</b>) and tricapped tetrahedral (<b>2</b>) geometries entrapped with an interstitial hydride, anchored by six ferrocene units at the periphery of the core. Compounds <b>3</b> and <b>4</b> comprise trimetallic Cu^I and dimetallic Ag^I cores enfolded by four and two ferrocene moieties. Interestingly both chelating and bridging modes of binding are observed for dppf ligand in <b>3</b>. Further the formation and isolation of polyhydrido copper clusters [Cu₂₈H₁₅{S₂CN^<i>i</i>PrCH₂Fc}₁₂]­(PF₆) (<b>5</b>) and [Cu₂₈H₁₅{S₂CN^<i>n</i>Bu₂}₁₂]­(PF₆) (<b>7</b>), stabilized by bulky ferrocenyl and <i>n</i>-butyl dithiocarbamate ligands, was demonstrated. They are readily identified by ²H NMR studies on their deuterium analogues, [Cu₂₈D₁₅{S₂CN^<i>i</i>PrCH₂Fc}₁₂]­(PF₆) (<b>6</b>) and [Cu₂₈D₁₅{S₂CN^<i>n</i>Bu₂}₁₂]­(PF₆) (<b>8</b>). Though the structure details as well as spectroscopic characterizations of <b>5</b> are yet to be investigated, the compound <b>7</b> is fully characterized by variety of spectroscopy including single-crystal X-ray diffraction. The cyclic voltammetry studies for compounds <b>1</b>, <b>2</b>, and <b>4</b> display irreversible redox peaks for Fe²⁺/Fe³⁺ couple wherein the reduction peaks are not well-resolved due to some adsorption of the complex onto the electrode surface

Hydrido Copper Clusters Supported by Dithiocarbamates: Oxidative Hydride Removal and Neutron Diffraction Analysis of [Cu₇(H){S₂C(aza-15-crown-5)}₆]

Reactions of Cu­(I) salts with Na­(S₂CR) (R = N^<i>n</i>Pr₂, NEt₂, aza-15-crown-5), and (Bu₄N)­(BH₄) in an 8:6:1 ratio in CH₃CN solution at room temperature yield the monocationic hydride-centered octanuclear Cu^I clusters, [Cu₈(H)­{S₂CR}₆]­(PF₆) (R = N^<i>n</i>Pr₂, <b>1</b>_<b>H</b>; NEt₂, <b>2</b>_<b>H</b>; aza-15-crown-5, <b>3</b>_<b>H</b>). Further reactions of [Cu₈(H)­{S₂CR}₆]­(PF₆) with 1 equiv of (Bu₄N)­(BH₄) produced neutral heptanuclear copper clusters, [Cu₇(H)­{S₂CR}₆] (R = N^<i>n</i>Pr₂, <b>4</b>_<b>H</b>; NEt₂, <b>5</b>_<b>H</b>; aza-15-crown-5, <b>6</b>_<b>H</b>) and clusters <b>4</b>–<b>6</b> can also be generated from the reaction of Cu­(BF₄)₂, Na­(S₂CR), and (Bu₄N)­(BH₄) in a 7:6:8 molar ratio in CH₃CN. Reformation of cationic Cu^I₈ clusters by adding 1 equiv of Cu^I salt to the neutral Cu₇ clusters in solution is observed. Intriguingly, the central hydride in [Cu₈(H)­{S₂CN^<i>n</i>Pr₂}₆]­(PF₆) can be oxidatively removed as H₂ by Ce­(NO₃)₆^2– to yield [Cu^II(S₂CN^<i>n</i>Pr₂)₂] exploiting the redox-tolerant nature of dithiocarbamates. Regeneration of hydride-centered octanuclear copper clusters from the [Cu^II(S₂CN^<i>n</i>Pr₂)₂] can be achieved by reaction with Cu­(I) ions and borohydride. The hydride release and regeneration of Cu^I₈ was monitored by UV–visible titration experiments. To our knowledge, this is the first time that hydride encapsulated within a copper cluster can be released as H₂ via chemical means. All complexes have been fully characterized by ¹H NMR, FT-IR, UV–vis, and elemental analysis, and molecular structures of <b>1</b>_<b>H</b>, <b>2</b>_<b>H</b>, and <b>6</b>_<b>H</b> were clearly established by single-crystal X-ray diffraction. Both <b>1</b>_<b>H</b> and <b>2</b>_<b>H</b> exhibit a tetracapped tetrahedral Cu₈ skeleton, which is inscribed within a S₁₂ icosahedron constituted by six dialkyl dithiocarbamate ligands in a tetrametallic-tetraconnective (μ₂, μ₂) bonding mode. The copper framework of <b>6</b>_<b>H</b> is a tricapped distorted tetrahedron in which the four-coordinate hydride is demonstrated to occupy the central site by single crystal neutron diffraction. Compounds <b>1</b>–<b>3</b> exhibit a yellow emission in both the solid state and in solution under UV irradiation at 77 K, and the structureless emission is assigned as a ³metal to ligand charge transfer (MLCT) excited state. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on model compounds match the experimental structures and provide rationalization of their bonding and optical properties

Lattice-Hydride Mechanism in Electrocatalytic CO₂ Reduction by Structurally Precise Copper-Hydride Nanoclusters

Copper electrocatalysts can reduce CO₂ to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO₂ reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as Cu₃₂H₂₀L₁₂ (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO₂ reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO₂ to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the predictions, electrochemical tests of CO₂ reduction on the Cu₃₂H₂₀L₁₂ cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H₂ production dominates at higher overpotential. The unique selectivity afforded by the lattice-hydride mechanism opens the door for further fundamental and applied studies of electrocatalytic CO₂ reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides