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

Gold(I) Alkynyls Supported by Mono- and Bidentate NHC Ligands: Luminescence and Isolation of Unprecedented Ionic Complexes

Reactions of NHC·HX (NHC = 1-benzyl-3-methylbenzimidazol-2-ylidene, X = Br^–, PF₆^–) and (AuCCR)_<i>n</i> (R = Ph, C₃H₆OH) in the presence of Cs₂CO₃ initially afford compounds of the general formula [(NHC)₂Au]₂[(RC₂)₂Au]­X, which can be isolated by crystallization. With increased reaction time, only the expected mononuclear complexes of the type [NHCAuCCR] are produced. The crystal structure of [(NHC)₂Au]₂[(PhC₂)₂Au]­PF₆ reveals an unprecedented triple-decker array upheld by a remarkably short (2.9375(7) Å) unsupported Au···Au···Au contact. The mononuclear complex [NHCAuCCPh] was found to crystallize as three distinct polymorphs and a pseudopolymorph, which depending on the intermolecular Au···Au distances emit blue, green, or yellow light. Two synthetic approaches were employed for the preparation of a series of dinuclear NHC-ligated Au­(I) alkynyl complexes of the general formula [NHC-(CH₂)_<i>n</i>-NHC­(AuCCR)₂], where NHC = <i>N</i>-benzylbenzimidazol-2-ylidene, R = Ph, C₃H₆OH, C₆H₁₀OH, and <i>n</i> = 1–3. In solution, the complexes with aliphatic substituents on the alkynyl fragment are nonemissive, whereas their phenyl-bearing congeners demonstrate characteristic metal-perturbed ³[IL­(CCPh)] emission. In the solid state, a clear correlation between intermolecular aurophilic interactions and luminescence was established, including their role in the luminescent thermochromism of the phenylalkynyl complexes. The relationship between the Au···Au distance and emission energy was found to be <i>inverse</i>: i.e., the shorter the aurophilic contact, the higher the emission energy. We tentatively attribute this behavior to a smaller extent of excited-state distortion for a structure with a shorter Au···Au separation

Aurophilicity in Action: Fine-Tuning the Gold(I)–Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)–NHC Complexes

The solution-state emission profiles of a series of dinuclear Au­(I) complexes <b>4</b>–<b>6</b> of the general formula Au₂(NHC-(CH₂)_<i>n</i>-NHC)₂Br₂, where NHC = <i>N</i>-benzylbenzimidazol-2-ylidene and <i>n</i> = 1–3, were found to be markedly different from each other and dependent on the presence of excess bromide. The addition of excess bromide to the solutions of <b>4</b> and <b>6</b> leads to red shifts of ca. 60 nm, and in the case of <b>5</b>, which is nonemissive when neat, green luminescence emerges. A detailed computational study undertaken to rationalize the observed behavior revealed the determining role aurophilicity plays in the photophysics of these compounds, and the formation of exciplexes between the complex cations and solvent molecules or counterions was demonstrated to significantly decrease the Au–Au distance in the triplet excited state. A direct dependence of the emission wavelength on the strength of the intracationic aurophilic contact allows for a controlled manipulation of the emission energy by varying the linker length of a diNHC ligand and by judicial choice of counterions or solvent. Such unique stimuli-responsive solution-state behavior is of interest to prospective applications in medical diagnostics, bioimaging, and sensing. In the solid, the investigated complexes are intensely phosphorescent and, notably, <b>5</b> and <b>6</b> exhibit reversible luminescent mechanochromism arising from amorphization accompanied by the loss of co-crystallized methanol molecules. The mechano-responsive properties are also likely to be related to changes in bromide coordination and the ensuing alterations of intramolecular aurophilic interactions. Somewhat surprisingly, the photophysics of NHC ligand precursors <b>2</b> and <b>3</b> is related to the formation of ground-state associates with bromide counterions through hydrogen bonding, whereas <b>1</b> does not appear to bind its counterions

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

Toward Luminescence Vapochromism of Tetranuclear Au^I–Cu^I Clusters

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC­(PPh₂)₃Au₃Cu­(C₂R)₃]⁺ (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu^t (<b>3</b>), cyclohexanolyl (<b>4</b>), cyclopentanolyl (<b>5</b>), 2,6-dimethylheptanolyl (<b>6</b>), 2-methylbutanolyl (<b>7</b>), diphenylmethanolyl (<b>8</b>)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC₂R)_<i>n</i> acetylides with the (PPh₂)₃CH ligand in the presence of Cu⁺ ions and NEt₃. Addition of Cl^– or Br^– anions to complex <b>8</b> results in coordination of the halides to the copper atoms to give neutral HC­(PPh₂)₃Au₃CuHal­(C₂COHPh₂)₃ derivatives (Hal = Cl (<b>9</b>), Br (<b>10</b>)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of <b>1</b>, <b>4</b>, <b>7</b>, and <b>8</b> were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80%. Exposure of the solvent-free X-ray amorphous samples <b>8</b>–<b>10</b> (R = diphenylmethanolyl) to vapors of the polar solvents (methanol, THF, acetone) switches luminescence with a visible hypsochromic shift of emission of 50–70 nm. The vapochromism observed is tentatively ascribed to the formation of a structurally ordered phase upon absorption of organic molecules by the amorphous solids

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

Toward Luminescence Vapochromism of Tetranuclear Au^I–Cu^I Clusters

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC­(PPh₂)₃Au₃Cu­(C₂R)₃]⁺ (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu^t (<b>3</b>), cyclohexanolyl (<b>4</b>), cyclopentanolyl (<b>5</b>), 2,6-dimethylheptanolyl (<b>6</b>), 2-methylbutanolyl (<b>7</b>), diphenylmethanolyl (<b>8</b>)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC₂R)_<i>n</i> acetylides with the (PPh₂)₃CH ligand in the presence of Cu⁺ ions and NEt₃. Addition of Cl^– or Br^– anions to complex <b>8</b> results in coordination of the halides to the copper atoms to give neutral HC­(PPh₂)₃Au₃CuHal­(C₂COHPh₂)₃ derivatives (Hal = Cl (<b>9</b>), Br (<b>10</b>)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of <b>1</b>, <b>4</b>, <b>7</b>, and <b>8</b> were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80%. Exposure of the solvent-free X-ray amorphous samples <b>8</b>–<b>10</b> (R = diphenylmethanolyl) to vapors of the polar solvents (methanol, THF, acetone) switches luminescence with a visible hypsochromic shift of emission of 50–70 nm. The vapochromism observed is tentatively ascribed to the formation of a structurally ordered phase upon absorption of organic molecules by the amorphous solids

Solid-State and Solution Metallophilic Aggregation of a Cationic [Pt(NCN)L]⁺ Cyclometalated Complex

The noncovalent intermolecular interactions (π–π stacking, metallophilic bonding) of the cyclometalated complexes [Pt­(NCN)­L]⁺X^– (NCN = dipyridylbenzene, L = pyridine (<b>1</b>), acetonitrile (<b>2</b>)) are determined by the steric properties of the ancillary ligands L in the solid state and in solution, while the nature of the counterion X^– (X^– = PF₆^–, ClO₄^–, CF₃SO₃^–) affects the molecular arrangement of <b>2</b>·X in the crystal medium. According to the variable-temperature X-ray diffraction measurements, the extensive Pt···Pt interactions and π-stacking in <b>2</b>·X are significantly temperature-dependent. The variable concentration ¹H and diffusion coefficients NMR measurements reveal that <b>2</b>·X exists in the monomeric form in dilute solutions at 298 K, while upon increase in concentration [Pt­(NCN)­(NCMe)]⁺ cations undergo the formation of the ground-state oligomeric aggregates with an average aggregation number of ∼3. The photoluminescent characteristics of <b>1</b> and <b>2</b>·X are largely determined by the intermolecular aggregation. For the discrete molecules the emission properties are assigned to metal perturbed IL charge transfer mixed with some MLCT contribution. In the case of oligomers <b>2</b>·X the luminescence is significantly red-shifted with respect to <b>1</b> and originates mainly from the ³MMLCT excited states. The emission energies depend on the structural arrangement in the crystal and on the complex concentration in solution, variation of which allows for the modulation of the emission color from greenish to deep red. In the solid state the lability of the ligands L leads to vapor-induced reversible transformation <b>1</b> ↔ <b>2</b> that is accompanied by the molecular reorganization and, consequently, dramatic change of the photophysical properties. Time-dependent density functional theory calculations adequately support the models proposed for the rationalization of the experimental observations

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

Chromophore-Functionalized Phenanthro-diimine Ligands and Their Re(I) Complexes

A series of diimine ligands has been designed on the basis of 2-pyridyl-1<i>H</i>-phenanthro­[9,10-<i>d</i>]­imidazole (<b>L1</b>, <b>L2</b>). Coupling the basic motif of <b>L1</b> with anthracene-containing fragments affords the bichromophore compounds <b>L3</b>–<b>L5</b>, of which <b>L4</b> and <b>L5</b> adopt a donor–acceptor architecture. The latter allows intramolecular charge transfer with intense absorption bands in the visible spectrum (lowest λ_abs 464 nm (ε = 1.2 × 10⁴ M^–1 cm^–1) and 490 nm (ε = 5.2 × 10⁴ M^–1 cm^–1) in CH₂Cl₂ for <b>L4</b> and <b>L5</b>, respectively). <b>L1</b>–<b>L5</b> show strong fluorescence in a fluid medium (Φ_em = 22–92%, λ_em 370–602 nm in CH₂Cl₂); discernible emission solvatochromism is observed for <b>L4</b> and <b>L5</b>. In addition, the presence of pyridyl (<b>L1</b>–<b>L5</b>) and dimethylaminophenyl (<b>L5</b>) groups enables reversible alteration of their optical properties by means of protonation. Ligands <b>L1</b>–<b>L5</b> were used to synthesize the corresponding [Re­(CO)₃X­(diimine)] (X = Cl, <b>1</b>–<b>5</b>; X = CN, <b>1</b>-<b>CN</b>) complexes. <b>1</b> and <b>2</b> exhibit unusual dual emission of singlet and triplet parentage, which originate from independently populated ¹ππ* and ³MLCT excited states. In contrast to the majority of the reported Re­(I) carbonyl luminophores, complexes <b>3</b>–<b>5</b> display moderately intense ligand-based fluorescence from an anthracene-containing secondary chromophore and complete quenching of emission from the ³MLCT state presumably due to the triplet–triplet energy transfer (³MLCT → ³ILCT)