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

[M₁₆Ni₂₄(CO)₄₀]^4–: Coinage Metal Tetrahedral Superatoms as Useful Building Blocks Related to Pyramidal Au₂₀ Clusters (M = Cu, Ag, Au). Electronic and Bonding Properties from Relativistic DFT Calculations

Characterization of the tetrahedral Au₂₀ structure in the gas phase remains a major landmark in gold cluster chemistry, where further efforts to stabilize this bare 20-electron superatom in solution to extend and understand its chemistry have failed so far. Here, we account for the structural, electronic, and bonding properties of [M₁₆Ni₂₄(CO)₄₀]^4– (M = Cu, Ag, Au) observed in solution for gold and silver. Our results show a direct electronic relationship with Au₂₀, owing that such species share a common tetrahedral [M₁₆]^4– central core with a 1S²1P⁶1D¹⁰2S² jellium configuration. In the case of Au₂₀, the [Au₁₆]^4– core is capped by four Au⁺ ions, whereas in [M₁₆Ni₂₄(CO)₄₀]^4– it is capped by four Ni₆(CO)₁₀ units. In both cases, the capping entities are a full part of the superatom entity, where it appears that the free (uncapped) [M₁₆]^4– species must be capped for further stabilization. It follows that the Ni₆(CO)₁₀ units in [M₁₆Ni₂₄(CO)₄₀]^4– should not be considered as external ligands as their bonding with the [M₁₆]^4– core is mainly associated with a delocalization of the 20 jellium electrons onto the Ni atoms. Thus, the [M₁₆Ni₂₄(CO)₄₀]^4– species can be seen as the solution version of tetrahedral M₂₀ clusters, encouraging experimental efforts to further develop the chemistry of such complexes as M(111) finite surface section structures, with M = Ag and Au and, particularly promising, with M = Cu. Furthermore, optical properties were simulated to assist future experimental characterization

New Main-Group-Element-Rich <i>nido</i>-Octahedral Cluster System: Synthesis and Characterization of [Et₄N][Fe₂(CO)₆(μ₃‑As){μ₃‑EFe(CO)₄}₂]

A series of clusters of the form [Et₄N]­[Fe₂­(CO)₆­(μ₃-As)}­(μ₃-EFe­(CO)₄)], where E is either P or As, were synthesized from [Et₄N]₂­[HAs­{Fe­(CO)₄}₃] and ECl₃. AsCl₃ gives the As-only compound; PCl₃ produces compounds having two As atoms with one P atom, or one As atom and two P atoms, and they can exist as two possible isomers, one of which is chiral. The As₂P and AsP₂ clusters cocrystallize, and their structure as determined by single-crystal X-ray diffraction is given along with the structure of the As-only cluster. Analytical data as well as density functional theory calculations support the formation and geometries of the new molecules

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

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

[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