Sergey P. Tunik

Self-Assembly of Supramolecular Luminescent AuI–CuI Complexes: “Wrapping” an Au6Cu6 Cluster in a [Au3(diphosphine)3]3+ “Belt”†

Growing attention to alkynyl complexes of coinage metals, stimulated by their intriguing photophysical properties, has substantially focused on polynuclear homoand heterometallic compounds. The versatile bonding mode of alkynes and metallophilic interactions resulted in the synthesis of numerous cluster complexes which display different structural motifs and emission properties. 9,11] However, in most cases assembly of the complexes occurs in an uncontrolled way 11] and therefore it is a challenge to find a synthetic approach which would allow directed modification of the structural and electronic properties of these compounds. One of the most attractive features of supramolecular construction is the possible tuning of the luminescent behavior through changes in the electron richness of the alkyne ligands by p coordination to different metal ions. This method has been successfully used to synthesize heterometallic complexes by coordination of phosphine–gold(I)– alkyne p-donor metalloligands to d metal centers. These examples of alkynyl p coordination do not lead to ligand rearrangement, and the products formed obey the simple stoichiometry of the reaction. Composition and structure of the metal frameworks of these complexes are mainly determined by the steric properties of the phosphine ligands coordinated to the gold(I) center. This inspired our interest in probing rigid diphosphine ligands for the preparation of Au–alkynyl complexes containing spatially separated Au centers and studying their reactivity towards Cu ions. Herein we report the stepwise synthesis, structural characterization, and luminescence properties of Au–Cu supramolecular complexes self-assembled from simple Au and Cu precursors. Complex [Au2(C CPh)2(m-4,4’-Ph2PC6H4C6H4PPh2)] (1) was obtained by treating polymeric gold phenylacetylide [AuC CPh]n with the diphosphine. X-ray diffraction on 1 revealed a dimeric structure (Figure 1), similar to that found for analogous gold complexes based on the 1,2bis(diphenylphosphanyl)ethane ligand. However, the spectroscopic data (see the Supporting Information) indicate dissociation of the Au Au bonds in solution.

Octanuclear gold(I) alkynyl-diphosphine clusters showing thermochromic luminescence

The unprecedented, purely gold(I) alkynyl-diphosphine clusters 1-3 demonstrate intense room-temperature phosphorescence with maximum quantum efficiency of 92% in solution (3) and 86% in solid (2) and thermally dependent emission in the crystalline form, attributed to the crystal lattice arrangement.

Rational reductive fusion of two heterometallic clusters: formation of a highly stable, intensely phosphorescent Au–Ag aggregate and application in two-photon imaging in human mesenchymal stem cells

An unprecedented Au-Ag alkynyl-diphosphine aggregate, obtained via CO-reduction of a mixture of simple reagents, exhibits intense room-temperature phosphorescence free from O(2) quenching, and serves as an excellent phosphorescence dye suited for both one- and two-photon imaging in human stem cells.

An intensely and oxygen independent phosphorescent gold(I)-silver(I) complex: "trapping'' an Au8Ag10 oligomer by two gold-alkynyl-diphosphine molecules

The molecular heterometallic [{Au(8)Ag(10)(C(2)Ph)(16)}{(PhC(2)Au)(2)PPh(2)(C(6)H(4))(3)PPh(2)}(2)](2+) aggregate of unprecedented topology was obtained and structurally characterized; this compound demonstrates unusually effective phosphorescence, which displays negligible oxygen quenching due to shielding of emissive central cluster by the outer shell of the molecule.

Highly Luminescent Octanuclear AuI–CuI Clusters Adopting Two Structural Motifs: The Effect of Aliphatic Alkynyl Ligands

Reactions of the homoleptic (AuC(2)R)(n) precursors with stoichiometric amount of diphosphine ligand PPh(2)C(6)H(4)PPh(2) (P^P) and Cu(+) ions lead to an assembly of a new family of bimetallic clusters [Au(6)Cu(2)(C(2)R)(6)(P^P)(2)](2+) (type I; R=9-fluorenolyl (1), diphenylmethanolyl (2), 2,6-dimethyl-4-heptanolyl (3), 1-cyclohexanolyl (4), Cy (5), tBu (6)). In the case of R=1-cyclohexanolyl, a structurally different complex [Au(6)Cu(2)(C(2)C(6)H(11)O)(6)(P^P)(3)](2+) (7, type II) could be obtained by treatment of 4 with one equivalent of the diphosphine, while for R=isopropanolyl only the latter type of cluster [Au(6)Cu(2)(C(2)C(3)H(7)O)(6)(P^P)(3)](2+) (8) was detected. Steric bulkiness of the alkynyl ligands and O···H-O hydrogen bonding are suggested to play an important role in stabilizing the type I and type II cluster structural motif, respectively. All the complexes exhibit intense photoluminescence in solution with emission parameters that depending on the geometrical arrangement of the octanuclear metal core. The clusters 1-4 and 6 show single emission band in a blue region (469-488 nm) with maximum quantum yield of 94% (4), while structurally different 7 and 8 emit yellow-orange (590 nm) with unity quantum efficiency. The theoretical DFT calculations of the electronic structures have been carried out to demonstrate that the metal-centered triplet emission within the heterometallic core plays a key role for the observed phosphorescence.

Reactions of diacetylene ligands with trinuclear clusters. I Reactions of 2,4-hexadiyne-1,6-diol and its dicobalthexacarbonyl derivatives with H2Os3(CO)10

Abstract Reactions of H 2 Os 3 (CO) 10 with the diyne ligand HOCH 2 C 2 C 2 CH 2 OH and its dicobalthexacarbonyl derivatives {CO 2 (CO) 6 }(μ 2 ,η 2 -HOCH 2 C 2 C 2 CH 2 OH) and {Co 2 (CO) 6 } 2 (μ 2 ,η 2 : μ 2 ,η 2 -HOCH 2 C 2 C 2 CH 2 OH) have been studied. The reaction of the uncomplexed ligand yields the cluster with the completely rearranged starting ligand. The structure of this compound was determined by a single-crystal X-ray study. The rearranged ligand forms a pseudo-furan ring with the C CH 3 substituent in the α-position. The reactions of H 2 Os 3 (CO) 10 with the both dicobalthexacarbonyl derivatives yield the (μ-H)(μ-OH)Os 3 (CO) 10 cluster ar the main osmium-containing product. The structure of this compound was also established by a single-crystal X-ray study.

Intensely luminescent homoleptic alkynyl decanuclear gold(I) clusters and their cationic octanuclear phosphine derivatives.

Treatment of Au(SC(4)H(8))Cl with a stoichiometric amount of hydroxyaliphatic alkyne in the presence of NEt(3) results in high-yield self-assembly of homoleptic clusters (AuC(2)R)(10) (R = 9-fluorenol (1), diphenylmethanol (2), 2,6-dimethyl-4-heptanol (3), 3-methyl-2-butanol (4), 4-methyl-2-pentanol (4), 1-cyclohexanol (6), 2-borneol (7)). The molecular compounds contain an unprecedented catenane metal core with two interlocked 5-membered rings. Reactions of the decanuclear clusters 1-7 with gold-diphosphine complex [Au(2)(1,4-PPh(2)-C(6)H(4)-PPh(2))(2)](2+) lead to octanuclear cationic derivatives [Au(8)(C(2)R)(6)(PPh(2)-C(6)H(4)-PPh(2))(2)](2+) (8-14), which consist of planar tetranuclear units {Au(4)(C(2)R)(4)} coupled with two fragments [AuPPh(2)-C(6)H(4)-PPh(2)(AuC(2)R)](+). The titled complexes were characterized by NMR and ESI-MS spectroscopy, and the structures of 1, 13, and 14 were determined by single-crystal X-ray diffraction analysis. The luminescence behavior of both Au(I)(10) and Au(I)(8) families has been studied, revealing efficient room-temperature phosphorescence in solution and in the solid state, with the maximum quantum yield approaching 100% (2 in solution). DFT computational studies showed that in both Au(I)(10) and Au(I)(8) clusters metal-centered Au → Au charge transfer transitions mixed with some π-alkynyl MLCT character play a dominant role in the observed phosphorescence.

Stepwise 1D Growth of Luminescent Au(I)−Ag(I) Phosphine−Alkynyl Clusters: Synthesis, Photophysical, and Theoretical Studies

Reactions between the diphosphino-gold cationic complexes [Au(2)(PPh(2)-C(2)-(C(6)H(4))(n)-C(2)-PPh(2))(2)](2+) (n = 0, 1, 2, 3) and polymeric acetylides (AuC(2)Ph)(n) and (AgC(2)Ph)(n) lead to the formation of a new family of heterometallic clusters with the general formula [Au(8+2n)Ag(6+2n)(C(2)Ph)(8+4n)(PPh(2)C(2)(C(6)H(4))(n)C(2)PPh(2))(2)](2+), n = 0 (1), 1 (2), 2 (3), 3 (4). Compounds 1-4 were characterized in detail by NMR and ESI-MS spectroscopy. Complex 1 (n = 0) crystallizes in two forms (orange (1a) and yellow (1b)), one of which (1a) has been analyzed by X-ray crystallography. The luminescence behavior of 1-4 has been studied. Compounds 2 and 3 exhibited orange-red phosphorescence with quantitative quantum efficiency in both aerated and degassed CH(2)Cl(2), implying O(2)-independent phosphorescence due to efficient protection of the emitting chromophore center by the organic ligands. Complex 3 exhibits reasonable two-photon absorption (TPA) property with a cross section of σ ≈ 45 GM (800 nm), which is comparable to the value of commercially available TPA dyes such as coumarin 151. Computational studies have been performed to correlate the structural and photophysical features of the complexes studied. The metal-centered triplet emission within the heterometallic core is suggested to play a key role in the observed phosphorescence. The luminescence spectrum of 1 in CH(2)Cl(2) shows dual phosphorescence maximized at 575 nm (the P(1) band) and 770 nm (the P(2) band). Both P(1) and P(2) bands possess identical excitation spectra, i.e., the same ground-state origin, and the same relaxation dynamics throughout the temperature range of 298-200 K. The dual emission of 1 arises from fast structural fluctuation upon excitation, perhaps forming two geometry isomers, which exhibit distinctly different P(1) and P(2) bands. The scrambling dynamics might require large-amplitude motion and, hence, is hampered in rigid media, as evidenced by the single emission for 1a (610 nm) and 1b (570 nm) observed in solid.

Halogen Bonding to Amplify Luminescence: A Case Study Using A Platinum Cyclometalated Complex

The cocrystallization of a weakly luminescent platinum complex [Pt(btpy)(PPh3)Cl](1) (Hbtpy=2-(2benzothienyl)pyridine; emission quantum yield Φem=0.03) with fluorinated bromo- and iodoarenes C6F6-nXn (X=Br, I; n=1, 2) results in the formation of efficient halogen-bonding (XB) interactions Pt-Cl⋅⋅⋅X-R. An up to 22-fold enhancement (Φem =0.65) in the luminescence intensity of the cocrystallized compound is detected, without a substantial change of the emission energy. Based on crystallographic, photophysical, and theoretical investigations, the contribution of the XB donors C6F6-n Xn to the amplification of luminescence intensity is attributed to the enhancement of spin-orbit coupling through the heavy-atom effect, and simultaneously to the suppression of the nonradiative relaxation pathways by increasing the rigidity of the chromophore center.

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 (1), acetonitrile (2)) 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 2·X in the crystal medium. According to the variable-temperature X-ray diffraction measurements, the extensive Pt···Pt interactions and π-stacking in 2·X are significantly temperature-dependent. The variable concentration (1)H and diffusion coefficients NMR measurements reveal that 2·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 1 and 2·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 2·X the luminescence is significantly red-shifted with respect to 1 and originates mainly from the (3)MMLCT 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 1 ↔ 2 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.