Antti J. Karttunen

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 [Au(2)Cu(2)(C(2)OHC(5)H(8))(4)](n) efficiently self-assembles from Au(SC(4)H(8))Cl, Cu(NCMe)(4)PF(6), and 1-ethynylcyclopentanol in the presence of NEt(3). This compound shows remarkably diverse polymorphism arising from the modulation of metallophilic interactions by organic solvents. Four crystalline forms, obtained from methanol (1a); ethanol, acetone, or choloroform (1b); toluene (1c); and diethyl ether or ethyl acetate (1d), demonstrate different photoluminescent characteristics. The solid-state quantum yields of phosphorescence (Φ) vary from 0.1% (1a) to 25% (1d), depending on the character of intermetallic bonding. The structures of 1b-d were determined by single-crystal X-ray diffraction. The ethanol (1b, Φ = 2%) and toluene (1c, Φ = 10%) solvates of [Au(2)Cu(2)(C(2)OHC(5)H(8))(4)](n) adopt octanuclear isomeric structures (n = 2), while 1d (Φ = 25%) is a solvent-free chain polymer built from two types of Au(4)Cu(4) 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 1b < 1c < 1d. The metallophilic contacts in 1a-d 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.

Structural Principles of Semiconducting Group 14 Clathrate Frameworks

We have performed a comprehensive theoretical investigation of the structural principles of semiconducting clathrate frameworks composed of the Group 14 elements carbon, silicon, germanium, and tin. We have investigated the basic clathrate frameworks, together with their polytypes, intergrowth clathrate frameworks, and extended frameworks based on larger icosahedral building blocks. Quantum chemical calculations with the PBE0 hybrid density functional method provided a clear overview of the structural trends and electronic properties among the various clathrate frameworks. In agreement with previous experimental and theoretical studies, the clathrate II framework proved to be the energetically most favorable, but novel hexagonal polytypes of clathrate II also proved to be energetically very favorable. In the case of silicon, several of the studied clathrate frameworks possess direct and wide band gaps. The band structure diagrams and simulated powder X-ray patterns of the studied frameworks are provided and systematic preliminary evaluation of guest-occupied frameworks is conducted to shed light on the characteristics of novel, experimentally feasible clathrate compositions.

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.

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.

Reactions of beryllium halides in liquid ammonia: the tetraammineberyllium cation [Be(NH3)4]2+, its hydrolysis products, and the action of Be2+ as a fluoride-ion acceptor.

The first structural characterization of the text-book tetraammineberyllium(II) cation [Be(NH(3))(4)](2+), obtained in the compounds [Be(NH(3))(4)](2)Cl(4)⋅17NH(3) and [Be(NH(3))(4)]Cl(2), is reported. Through NMR spectroscopic and quantum chemical studies, its hydrolysis products in liquid ammonia were identified. These are the dinuclear [Be(2)(μ-OH)(NH(3))(6)](3+) and the cyclic [Be(2)(μ-OH)(2)(NH(3))(4)](2+) and [Be(3)(μ-OH)(3)(NH(3))(6)](3+) cations. The latter species was isolated as the compound [Be(3)(μ-OH)(3)(NH(3))(6)]Cl(3)⋅7NH(3). NMR analysis of solutions of BeF(2) in liquid ammonia showed that the [BeF(2)(NH(3))(2)] molecule was the only dissolved species. It acts as a strong fluoride-ion acceptor and forms the [BeF(3)(NH(3))](-) anion in the compound [N(2)H(7)][BeF(3)(NH(3))]. The compounds presented herein were characterized by single-crystal X-ray structure analysis, (9)Be, (17)O, and (19)F NMR, IR, and Raman spectroscopy, deuteration studies, and quantum chemical calculations. The extension of beryllium chemistry to the ammine system shows similarities but also decisive differences to the aquo system.