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

Synthesis and Characterization of Hypoelectronic Tantalaboranes: Comparison of the Geometric and Electronic Structures of [(Cp*TaX)₂B₅H₁₁] (X = Cl, Br, and I)

Mild thermolysis of tantalaborane [(Cp*Ta)₂B₅H₁₁], <b>1</b> (Cp* = η⁵-C₅Me₅) in presence of halogen sources affords the open cage clusters [(Cp*TaX)₂B₅H₁₁], <b>2</b>–<b>4</b> (<b>2</b>: X = Cl; <b>3</b>: X = Br; and <b>4</b>: X = I) in good yields. In contrast, the tetraborohydride cluster, [(Cp*Ta)₂B₄H₉(μ-BH₄)], <b>5</b>, under the same reaction conditions forms the B–H substituted cluster [(Cp*Ta)₂B₄H₈I­(μ-BH₄)], <b>6</b>. All the new metallaboranes have been characterized by mass spectrometry, ¹H, ¹¹B, ¹³C NMR spectroscopy, and elemental analysis, and the structural types were established by crystallographic analysis of clusters <b>3</b>, <b>4</b>, and <b>6</b>. Density functional theory (DFT) calculations at the BP86/TZ2P ZORA level reveal geometries in agreement with the structure determinations, large gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in accord with their stabilities. B3LYP-computed ¹¹B chemical shifts accurately reflect the experimentally measured shifts. Clusters <b>2</b>–<b>4</b> can be viewed as 7-sep 7-vertex <i>oblatoarachno</i> M₂B₅ clusters which can be generated from a 7-sep 9-vertex <i>oblatocloso</i> M₂B₇ cluster by removal of two equatorial boron atoms. Cluster <b>6</b> can be considered as an electron-deficient 6-sep 6-vertex <i>oblatoarachno</i> M₂B₄ cluster derived from an 8-vertex <i>oblatocloso</i> hexagonal bipyramidal cluster, in which BH₄^– anion is weakly bonded in a bidentate mode

Synthesis and Characterization of Hypoelectronic Tantalaboranes: Comparison of the Geometric and Electronic Structures of [(Cp*TaX)₂B₅H₁₁] (X = Cl, Br, and I)

Mild thermolysis of tantalaborane [(Cp*Ta)₂B₅H₁₁], <b>1</b> (Cp* = η⁵-C₅Me₅) in presence of halogen sources affords the open cage clusters [(Cp*TaX)₂B₅H₁₁], <b>2</b>–<b>4</b> (<b>2</b>: X = Cl; <b>3</b>: X = Br; and <b>4</b>: X = I) in good yields. In contrast, the tetraborohydride cluster, [(Cp*Ta)₂B₄H₉(μ-BH₄)], <b>5</b>, under the same reaction conditions forms the B–H substituted cluster [(Cp*Ta)₂B₄H₈I­(μ-BH₄)], <b>6</b>. All the new metallaboranes have been characterized by mass spectrometry, ¹H, ¹¹B, ¹³C NMR spectroscopy, and elemental analysis, and the structural types were established by crystallographic analysis of clusters <b>3</b>, <b>4</b>, and <b>6</b>. Density functional theory (DFT) calculations at the BP86/TZ2P ZORA level reveal geometries in agreement with the structure determinations, large gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in accord with their stabilities. B3LYP-computed ¹¹B chemical shifts accurately reflect the experimentally measured shifts. Clusters <b>2</b>–<b>4</b> can be viewed as 7-sep 7-vertex <i>oblatoarachno</i> M₂B₅ clusters which can be generated from a 7-sep 9-vertex <i>oblatocloso</i> M₂B₇ cluster by removal of two equatorial boron atoms. Cluster <b>6</b> can be considered as an electron-deficient 6-sep 6-vertex <i>oblatoarachno</i> M₂B₄ cluster derived from an 8-vertex <i>oblatocloso</i> hexagonal bipyramidal cluster, in which BH₄^– anion is weakly bonded in a bidentate mode

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

[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

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