A Single-Crystal Model for MgCl₂–Electron Donor Support Materials: [Mg₃Cl₅(THF)₄Bu]₂ (Bu = <i>n</i>‑Butyl)

The influence of the electron donor tetrahydrofuran (THF) on the formation of the crystalline morphology of MgCl₂ was studied. MgCl₂ was synthesized from magnesium and 1-chlorobutane in the presence of THF with the THF/Mg molar ratio ranging from 0.063 to 2.0. With the highest amounts of THF crystalline particles were formed, as evidenced from scanning electron microscopy images. The X-ray structure analysis of these single crystals revealed the new organometallic Mg compound [Mg₃Cl₅(THF)₄Bu]₂ (Bu = <i>n</i>-butyl), which has an open dicubane-like structure with four octahedrally and two tetrahedrally coordinated Mg atoms. The compound also contains two butyl groups directly bound to the Mg atoms at the opposite corners of the dicubane structure. With the lowest THF amounts, structurally disordered MgCl₂/THF complexes were formed. The transition from single crystals toward particles with an amorphous morphology appeared to occur through an intermediate type of morphology with a three-dimensional network structure. The network structure is formed from a thin (30–100 nm) fiberlike MgCl₂/THF material. Infrared and solid-state ¹³C nuclear magnetic resonance spectroscopy measurements revealed different types of Mg sites present in the MgCl₂/THF complexes

Versatile Coordination Modes in Silver-Imidazolecarbaldehyde Oxime Complexes: Structural and Computational Analysis

Silver imidazolecarbaldehyde oxime complexes [Ag­(1-methyl-1<i>H</i>-imidazole-2-carbaldehyde oxime)₂]­[NO₃] (<b>1</b>), [Ag­(1-methyl-1<i>H</i>-imidazole-2-carbaldehyde oxime)₂]­[ClO₃] (<b>2</b>), [Ag­(1<i>H</i>-5-methylimidazole-4-carbaldehyde oxime)]₂­[NO₃]₂ (<b>3</b>), [Ag­(1<i>H</i>-imidazole-2-carbaldehyde oxime)]_<i>n</i>­[NO₃]_<i>n</i> (<b>4</b>), [Ag­(1<i>H</i>-4-methylimidazole-5-carbaldehyde oxime)]_<i>n</i>­[ClO₃]<i>_n</i> (<b>5</b>), and [Ag­(<i>N</i>-hydroxy-1-methyl-1<i>H</i>-imidazole-2-carboximidamide)₂]₂­[CF₃SO₃]₂ (<b>6</b>) were structurally and computationally analyzed. Weak intramolecular interactions were found to play the main role in determining the most favorable structure of the free ligands, therefore controlling the final coordination mode, and the nuclearity of the complexes. Further information on the nature of the intra- and intermolecular interactions were provided utilizing computational density functional theory calculations and topological charge density analysis according to the Quantum Theory of Atoms in Molecules. The efficient control of the structure of the complexes also results in a better control of the material properties

Modulation of Metallophilic Bonds: Solvent-Induced Isomerization and Luminescence Vapochromism of a Polymorphic Au–Cu Cluster

We report a homoleptic Au–Cu alkynyl cluster that represents an unexplored class of luminescent materials with stimuli-responsive photophysical properties. The bimetallic complex formulated as [Au₂Cu₂(C₂OHC₅H₈)₄]_<i>n</i> efficiently self-assembles from Au­(SC₄H₈)­Cl, Cu­(NCMe)₄PF₆, and 1-ethynylcyclopentanol in the presence of NEt₃. This compound shows remarkably diverse polymorphism arising from the modulation of metallophilic interactions by organic solvents. Four crystalline forms, obtained from methanol (<b>1a</b>); ethanol, acetone, or choloroform (<b>1b</b>); toluene (<b>1c</b>); and diethyl ether or ethyl acetate (<b>1d</b>), demonstrate different photoluminescent characteristics. The solid-state quantum yields of phosphorescence (Φ) vary from 0.1% (<b>1a</b>) to 25% (<b>1d</b>), depending on the character of intermetallic bonding. The structures of <b>1b</b>–<b>d</b> were determined by single-crystal X-ray diffraction. The ethanol (<b>1b</b>, Φ = 2%) and toluene (<b>1c</b>, Φ = 10%) solvates of [Au₂Cu₂(C₂OHC₅H₈)₄]_<i>n</i> adopt octanuclear isomeric structures (<i>n</i> = 2), while <b>1d</b> (Φ = 25%) is a solvent-free chain polymer built from two types of Au₄Cu₄ units. Electronic structure calculations show that the dramatic enhancement of the emission intensity is correlated with the increasing role of metal–metal bonding. The latter makes the emission progressively more metal-centered in the order <b>1b</b> < <b>1c</b> < <b>1d</b>. The metallophilic contacts in <b>1a</b>–<b>d</b> show high sensitivity to the vapors of certain solvents, which effectively induce unusual solid-state isomerization and switching of the absorption and luminescence properties via non-covalent interactions. The reported polymorphic material is the first example of a gold­(I) alkynyl compound demonstrating vapochromic behavior

Low-Nuclearity Alkynyl d¹⁰ Clusters Supported by Chelating Multidentate Phosphines

The coordination chemistry of the tri- and tetradentate chelating phosphines (2-PPh₂C₆H₄)₂P­(O)­Ph (<i><b>P</b></i>^<b>3</b><i><b>O</b></i>) and (2-PPh₂C₆H₄)₃P (<i><b>P</b></i>^<b>4</b>) with respect to d¹⁰ copper subgroup metal ions has been investigated. Depolymerization of (MC₂R)_<i>n</i> (M = Cu, Ag) with <i><b>P</b></i>^<b>4</b> affords the series of mono- and trinuclear complexes (<i><b>P</b></i>^<b>4</b>)­CuC₂Ph (<b>1</b>), (<i><b>P</b></i>^<b>4</b>)­Cu₃(C₂Ph)₃ (<b>2</b>), (<i><b>P</b></i>^<b>4</b>)­Ag₃(C₂Ph) (Hal)₂ (Hal = Cl (<b>3</b>), Br (<b>4</b>), I (<b>5</b>)). Reactions of the M⁺ (M = Cu, Ag) ions with (M′C₂R)_<i>n</i> (M′ = Cu, Ag, Au) acetylides in the presence of <i><b>P</b></i>^<b>4</b> yield the family of dinuclear species [(<i><b>P</b></i>^<b>4</b>)­MM′(C₂R)]⁺ (<b>6</b>–<b>12</b>), which comprise the Cu₂/Ag₂ (<b>6</b>, <b>7</b>; R = Ph), AuCu (<b>8</b>–<b>10</b>; R = Ph, C­(OH)­Me₂, C­(OH)­Ph₂), and AuAg (<b>11</b>, <b>12</b>; R = Ph, C­(OH)­Ph₂) metal cores. A related triphosphine, (2-PPh₂C₆H₄)₂PPh (<i><b>P</b></i>^<b>3</b>), applied in a similar protocol undergoes partial oxidation and leads to the heterotrimetallic clusters [{(<i><b>P</b></i>^{<i><b>3</b></i>}<i><b>O</b></i>)­M}₂Au­(C₂R)₂]⁺ (M = Cu, R = C­(OH)­Ph₂, <b>13</b>; M = Ag, R = C­(OH)­Ph₂, <b>14</b>; M = Ag, R = Ph, <b>15</b>), which can be prepared more efficiently starting from the oxidized ligand <i><b>P</b></i>^<b>3</b><i><b>O</b></i>. The structures of the complexes <b>1</b>–<b>4</b> and <b>6</b>–<b>15</b> were established by single-crystal X-ray crystallography. According to the variable-temperature ¹H and ³¹P­{¹H} NMR experiments, compounds <b>1</b>–<b>12</b> demonstrate fluxional behavior in solution. The title complexes do not show appreciable luminescence in solution at 298 K, and the photophysical properties of <b>1</b>–<b>15</b> were studied in the solid state. The observed phosphorescence (Φ_em up to 0.46, λ_em from 440 to 635 nm) is assigned to cluster-centered transitions mixed with some MLCT d → π*­(alkynyl) character

Modulation of Metallophilic Bonds: Solvent-Induced Isomerization and Luminescence Vapochromism of a Polymorphic Au–Cu Cluster

We report a homoleptic Au–Cu alkynyl cluster that represents an unexplored class of luminescent materials with stimuli-responsive photophysical properties. The bimetallic complex formulated as [Au₂Cu₂(C₂OHC₅H₈)₄]_<i>n</i> efficiently self-assembles from Au­(SC₄H₈)­Cl, Cu­(NCMe)₄PF₆, and 1-ethynylcyclopentanol in the presence of NEt₃. This compound shows remarkably diverse polymorphism arising from the modulation of metallophilic interactions by organic solvents. Four crystalline forms, obtained from methanol (<b>1a</b>); ethanol, acetone, or choloroform (<b>1b</b>); toluene (<b>1c</b>); and diethyl ether or ethyl acetate (<b>1d</b>), demonstrate different photoluminescent characteristics. The solid-state quantum yields of phosphorescence (Φ) vary from 0.1% (<b>1a</b>) to 25% (<b>1d</b>), depending on the character of intermetallic bonding. The structures of <b>1b</b>–<b>d</b> were determined by single-crystal X-ray diffraction. The ethanol (<b>1b</b>, Φ = 2%) and toluene (<b>1c</b>, Φ = 10%) solvates of [Au₂Cu₂(C₂OHC₅H₈)₄]_<i>n</i> adopt octanuclear isomeric structures (<i>n</i> = 2), while <b>1d</b> (Φ = 25%) is a solvent-free chain polymer built from two types of Au₄Cu₄ units. Electronic structure calculations show that the dramatic enhancement of the emission intensity is correlated with the increasing role of metal–metal bonding. The latter makes the emission progressively more metal-centered in the order <b>1b</b> < <b>1c</b> < <b>1d</b>. The metallophilic contacts in <b>1a</b>–<b>d</b> show high sensitivity to the vapors of certain solvents, which effectively induce unusual solid-state isomerization and switching of the absorption and luminescence properties via non-covalent interactions. The reported polymorphic material is the first example of a gold­(I) alkynyl compound demonstrating vapochromic behavior

Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

The experimental study of dechlorination activity of a Au/Ag bimetallic system has shown formation of a variety of chlorinated bimetallic Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It is the formation of the Au/Ag cluster species that mediated C–Cl bond breakage, since neither Au nor Ag species alone exhibited a comparable activity. The nature of the products and the mechanism of dechlorination were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations at the M06/6-311G­(d)&SDD level of theory. It was revealed that formation of bimetallic clusters facilitated dechlorination activity due to the thermodynamic factor: C–Cl bond breakage by metal clusters was thermodynamically favored and resulted in the formation of chlorinated bimetallic species. An appropriate Au:Ag ratio for an efficient hydrodechlorination process was determined in a joint experimental and theoretical study carried out in the present work. This mechanistic finding was followed by synthesis of molecular bimetallic clusters, which were successfully involved in the hydrodechlorination of CCl₄ as a low molecular weight environment pollutant and in the dechlorination of dichlorodiphenyl­trichloroethane (DDT) as an eco-toxic insecticide. High activity of the designed bimetallic system made it possible to carry out a dechlorination process under mild conditions at room temperature

Harvesting Fluorescence from Efficient T_<i>k</i> → S_<i>j</i> (<i>j</i>, <i>k</i> > 1) Reverse Intersystem Crossing for ππ* Emissive Transition-Metal Complexes

Using a bimetallic Au­(I) complex bearing alkynyl-(phenylene)₃-diphosphine ligand (<b>A</b>-<b>3</b>), we demonstrate that the fluorescence can be exquisitely harvested upon T₁ → T_<i>k</i> (<i>k</i> > 1) excitation followed by T_<i>k</i> → S_<i>j</i> (<i>j</i>, <i>k</i> > 1) intersystem crossing (ISC) back to the S₁ state. Upon S₀ → S₁ 355 nm excitation, the S₁ → T₁ intersystem crossing rate has been determined to be 8.9 × 10⁸ s^–1. Subsequently, in a two-step laser pump–probe experiment, following a 355 nm laser excitation, the 532 nm T₁ → T_<i>k</i> probing gives the prominent blue 375 nm fluorescence, and this time-dependent pump–probe signal correlates well with the lifetime of the T₁ state. Careful examination reveals the efficiency of T_<i>k</i> → S<i>_j</i> (<i>j</i>, <i>k</i> > 1) reverse intersystem crossing to be 5.2%. The result is rationalized by a mechanism incorporating substantial involvement of metal-to-ligand charge transfer (MLCT) in the T_<i>k</i> (S_<i>j</i>) states, enhancing the rate of T_<i>k</i> → S_<i>j</i> ISC, which is competitive with the rate of T_k → T₁ internal conversion. This mechanism is also proven to be operative in the <b>A</b>-<b>3</b> solid film and should be universally applicable to the transition-metal complexes possessing a dominant ππ* configuration in the lowest-lying states. From an energy point of view, the UV fluorescence (375 nm) generated by green (532 nm) excitation can be recognized as a signal up-conversion process

Silver Alkynyl-Phosphine Clusters: An Electronic Effect of the Alkynes Defines Structural Diversity

The face-capping triphosphine, 1,1,1-tris­(diphenyl­phos­phino)­methane (tppm), together with bridging alkynyl ligands and the counterions, facilitates the formation of a family of silver complexes, which adopt cluster frameworks of variable nuclearity. The hexanuclear compounds [Ag₆­(C₂­C₆H₄-4-X)₃­(tppm)₂­(An^–)₃] (X = H (<b>1</b>), CF₃ (<b>2</b>), OMe (<b>3</b>), An^– = CF₃SO₃^–; X = OMe (<b>4</b>), An^– = CF₃COO^–) are produced for the electron-accepting to moderately electron-donating alkynes and the appropriate stoichiometry of the reagents. <b>1</b> and <b>3</b> undergo an expansion of the metal core when treated with 1 equiv of Ag⁺ to give the species [Ag₇­(C₂­C₆H₄-4-X)₃­(tppm)₂­(CF₃­SO₃)₃]­(CF₃­SO₃) (X = H (<b>5</b>), OMe (<b>6</b>)). The electron-donating substituent (X = NMe₂) particularly favors this Ag₇ arrangement (<b>7</b>) that undergoes geometry changes upon alkynylation, resulting in the capped prismatic cluster [Ag₇­(C₂­C₆H₄-4-NMe₂)₄­(tppm)₂­(CF₃­SO₃)]­(CF₃­SO₃)₂ (<b>8</b>). Alternatively, for the aliphatic <i>^t</i>Bu-alkyne, only the octanuclear complex [Ag₈­(C₂Bu^<i>t</i>)₄­{(PPh₂)₃­CH}₂­(CF₃­SO₃)₂]­(CF₃­SO₃)₂ (<b>9</b>) is observed. The structures of <b>1</b>–<b>4</b> and <b>6</b>–<b>9</b> were determined by X-ray diffraction analysis. In solution, all the studied compounds were found to be stereochemically nonrigid that prevented their investigation in the fluid medium. In the solid state, clusters <b>2</b>, <b>3</b>, <b>5</b>–<b>8</b> exhibit room temperature luminescence of triplet origin (maximum Φ_em = 27%, λ_em = 485–725 nm). The observed emission is assigned mainly to [<i>d</i>(Ag) → π*­(alkyne)] electronic transitions on the basis of TD-DFT computational analysis

Silver Alkynyl-Phosphine Clusters: An Electronic Effect of the Alkynes Defines Structural Diversity

The face-capping triphosphine, 1,1,1-tris­(diphenyl­phos­phino)­methane (tppm), together with bridging alkynyl ligands and the counterions, facilitates the formation of a family of silver complexes, which adopt cluster frameworks of variable nuclearity. The hexanuclear compounds [Ag₆­(C₂­C₆H₄-4-X)₃­(tppm)₂­(An^–)₃] (X = H (<b>1</b>), CF₃ (<b>2</b>), OMe (<b>3</b>), An^– = CF₃SO₃^–; X = OMe (<b>4</b>), An^– = CF₃COO^–) are produced for the electron-accepting to moderately electron-donating alkynes and the appropriate stoichiometry of the reagents. <b>1</b> and <b>3</b> undergo an expansion of the metal core when treated with 1 equiv of Ag⁺ to give the species [Ag₇­(C₂­C₆H₄-4-X)₃­(tppm)₂­(CF₃­SO₃)₃]­(CF₃­SO₃) (X = H (<b>5</b>), OMe (<b>6</b>)). The electron-donating substituent (X = NMe₂) particularly favors this Ag₇ arrangement (<b>7</b>) that undergoes geometry changes upon alkynylation, resulting in the capped prismatic cluster [Ag₇­(C₂­C₆H₄-4-NMe₂)₄­(tppm)₂­(CF₃­SO₃)]­(CF₃­SO₃)₂ (<b>8</b>). Alternatively, for the aliphatic <i>^t</i>Bu-alkyne, only the octanuclear complex [Ag₈­(C₂Bu^<i>t</i>)₄­{(PPh₂)₃­CH}₂­(CF₃­SO₃)₂]­(CF₃­SO₃)₂ (<b>9</b>) is observed. The structures of <b>1</b>–<b>4</b> and <b>6</b>–<b>9</b> were determined by X-ray diffraction analysis. In solution, all the studied compounds were found to be stereochemically nonrigid that prevented their investigation in the fluid medium. In the solid state, clusters <b>2</b>, <b>3</b>, <b>5</b>–<b>8</b> exhibit room temperature luminescence of triplet origin (maximum Φ_em = 27%, λ_em = 485–725 nm). The observed emission is assigned mainly to [<i>d</i>(Ag) → π*­(alkyne)] electronic transitions on the basis of TD-DFT computational analysis