Highly luminescent octanuclear Au(I)-Cu(I) 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 gold(I)-silver(I) cluster complexes with tunable structural features

A new series of isostructural, brilliantly luminescent gold-silver complexes having the formula [Au3(mu3-E)Ag(PPh2py)3](BF4)2 where E = O, S, Se and Ph2Ppy = 2-diphenylphosphinopyridine has been synthesized and characterized. The structural core of these complexes is a Au3Ag metallophilically linked tetrahedron with a group-16 atom functioning as a mu3-ligand capping the three gold atoms. In the solid state, pairs of clusters are joined by two unsupported aurophilic interactions. The emission energy changes strikingly in going from O (blue) to S (yellow) and Se (orange). The luminescence from the E = O system is the first to be reported for a gold(I) oxo system. Additionally, the luminescent 4-methylpyridyl analogue with E = S has been prepared and structurally characterized. For E = S, Se, the change in emission energy with mu3-bridging atom provides a sound basis for an LMMCT assignment of the excited state while lifetime measurements support its spin-forbidden nature. Frozen glass measurements indicate the presence of a higher-energy emitting state for these systems, and for the E = O system, either LMMCT or metal-centered cluster-based emission can be proposed.     

Highly luminescent gold(I)-silver(I) and gold(I)-copper(I) chalcogenide clusters

The reactions of [AuClL] with Ag(2)O, where L represents the heterofunctional ligands PPh(2)py and PPh(2)CH(2)CH(2)py, give the trigoldoxonium complexes [O(AuL)(3)]BF(4). Treatment of these compounds with thio- or selenourea affords the triply bridging sulfide or selenide derivatives [E(AuL)(3)]BF(4) (E=S, Se). These trinuclear species react with Ag(OTf) or [Cu(NCMe)(4)]PF(6) to give different results, depending on the phosphine and the metal. The reactions of [E(AuPPh(2)py)(3)]BF(4) with silver or copper salts give [E(AuPPh(2)py)(3)M](2+) (E=O, S, Se; M=Ag, Cu) clusters that are highly luminescent. The silver complexes consist of tetrahedral Au(3)Ag clusters further bonded to another unit through aurophilic interactions, whereas in the copper species two coordination isomers with different metallophilic interactions were found. The first is analogous to the silver complexes and in the second, two [S(AuPPh(2)py)(3)](+) units bridge two copper atoms through one pyridine group in each unit. The reactions of [E(AuPPh(2)CH(2)CH(2)py)(3)]BF(4) with silver and copper salts give complexes with [E(AuPPh(2)CH(2)CH(2)py)(3)M](2+) stoichiometry (E=O, S, Se; M=Ag, Cu) with the metal bonded to the three nitrogen atoms in the absence of AuM interactions. The luminescence of these clusters has been studied by varying the chalcogenide, the heterofunctional ligand, and the metal.     

A homoleptic phosphine adduct of Tl(I)

A homoleptic phosphine adduct of thallium(I) supported by a tris(phosphino)borate ligand has been isolated and structurally characterized.     

Design and synthesis of luminescence chemosensors based on alkynyl phosphine gold(I)-copper(I) aggregates

Receptor-containing polynuclear mixed-metal complexes of gold(I)-copper(I) 1-3 based on a [{Au(3)Cu(2)(C≡CPh)(6)}Au(3){PPh(2)-C(6)H(4)-PPh(2)}(3)](2+) (Au(6)Cu(2)) core with benzo-15-crown-5, oligoether and urea binding sites were designed and synthesized, respectively. These complexes exhibited remarkably strong red emission at ca. 619-630 nm in dichloromethane solution at room temperature upon photoexcitation at λ > 400 nm, with the emission quantum yield in the range 0.59-0.85. The cation-binding properties of 1 and 2 and the anion-binding properties of 3 were studied using UV-vis, emission and (1)H NMR techniques. Complex 1, with six benzo-15-crown-5 pendants, was found to show a higher binding preference for K(+), with a selectivity trend of K(+)? Cs(+) > Na(+) > Li(+). The addition of metal ions (Li(+), Na(+), K(+) and Cs(+)) to complex 1 led to a modest emission enhancement with a concomitant slight blue shift in energy and well-defined isoemissive points, which is attributed to the rigidity of the structure and the inhibited PET (photo-induced electron transfer) process from the oxygen to the aggregate as a result of the binding of the metal ion. The six urea receptor groups on complex 3 were found to form multiple hydrogen bonding interactions with anions, with the positive charge providing additional electrostatic interaction for anion-binding. The anion selectivity of 3 follows the trend F(-) > Cl(-)≈ H(2)PO(4)(-) > Br(-) and the highest affinity towards F(-) is attributed to the stronger basicity of F(-), as well as its good size match with the cavity of the urea pocket.     

The first homoleptic gold(I) thiosulfonate complex

A gold(I) thiosulfonate complex, Et(4)N[Au(MeS(2)O(2))(2)], is reported in which gold(I) ions are coordinated by the terminal sulfur atoms from two MeS(2)O(2)(-) ligands in a linear geometry. Two anionic units are linked by an aurophilic interaction forming discrete anionic dimers, [Au(MeS(2)O(2))(2)](2)(2-), which exhibit a shorter Au···Au distance (by 0.2 ?) and smaller dihedral angle than the thiosulfate analogue.     

On the biological properties of alkynyl phosphine gold(i) complexes

Golden times for metal-based drugs? Alkynyl triphenylphosphine gold(I) complexes display interesting biological properties and show high potential for future drug development. They are strong inhibitors of the enzyme thioredoxin reductase, trigger antiproliferative effects in tumor cells, and influence tumor cell metabolism, mitochondrial respiration, and angiogenesis in zebrafish embryos.     

Synthesis and characterization of perhalophenyltin derivatives. Study of their reactivity toward phosphine gold(I) chlorides

The (perhalophenyl)tin derivatives [SnR₄] (1-3) and [SnR₃Cl] (4-6) (R = C₆F₅, C₆F₃Cl₂, C₆Cl₅) were prepared from SnCl₄ and LiR or [SnR₄] in the appropriate molar ratio, while the dinuclear complexes [SnR₃]₂ (7-9) were obtained by treatment of [SnR₃Cl] with potassium under toluene reflux. Complexes 2, 6·0.5toluene and 7 were structurally characterized, the latter displaying a Sn-Sn bond of 2.808(7) Å, which indicates a strong tin-tin bond with covalent character in solid state. The hexaaryldistannanes 7-9 undergo transmetallation reactions with gold(I) derivatives, such as [AuCl(PPh₃)] or [(AuCl)₂(μ-dppm)], affording the neutral species [AuR(PPh₃)] (10-12) or [(AuR)₂(μ-dppm)] (13-15) or the ionic product [Au₃Cl₂(μ-dppm)₂][Sn(C₆F₅)₃Cl₂] (16). The crystal structures of 14·CH₂Cl₂, 15 and 16·2CH₂Cl₂ were determined by X-ray diffraction, the latter showing a Au₃ nearly equilateral triangular core in the cation with gold-gold contacts of 3.128(7) and 3.227(12) Å. The main difference between the molecular structures of 14·CH₂Cl₂ and 15 (both of them displaying intramolecular gold-gold contacts of 3.142(6) and 3.160(4) Å, respectively) is the presence of an intermolecular Au?Au interaction of 3.2126(8) Å in the case of the C₆F₃Cl₂ complex that gives rise to a tetranuclear unit.     

Branched carbon-rich luminescent multinuclear platinum(II) and palladium(II) alkynyl complexes with phosphine ligands

In this review, the synthesis, electronic absorption and luminescent properties of a series of branched alkynylpalladium(II) and -platinum(II) phosphine complexes with different alkynyl backbones and some of their structurally related complexes in the literature will be discussed. With the growing research interest in the potential application of these complexes in the field of non-linear optics (NLO), the two-photon absorption (TPA) properties and the corresponding structure–property relationships of selected luminescent branched platinum(II) bis-alkynyl complexes will also be described.     

Different phosphorescent excited states of tetra- and octanuclear dendritic-like phosphine gold(I) thiolate complexes: photophysical and theoretical studies

The study of the photophysical properties of dendritic-like phosphinothiolate gold(I) complexes has been carried out. The studied complexes are two series of analogous compounds bearing 4 or 8 metal centers: the tetranuclear [Au(4)(S-C(6)H(4)-X)(4){DAB-G0-(PPh(2))(4)}] (X = F (3), MeO (4), Me (5) and NO(2) (6)) and the octanuclear [Au(8)(S-C(6)H(4)-X)(8){DAB-G1-(PPh(2))(8)}] (X = F (9), MeO (10), Me (11) and NO(2) (12)) complexes. All compounds are brightly luminescent in solid state at 77 K displaying lifetimes in the microsecond range. The correlation between the substituent in position four of the benzenethiolate ligand and the emission energy shows that the emissions arise from (3)[pπ(S)→pσ(Au)] or from intra-ligand (3)[π(S)→π*(C(6)H(4)X)] charge transfer transitions, depending on the substituents. Theoretical DFT-B3LYP, ONIOM (DFT-B3LYP/UFF) and ONIOM (MP2/UFF) calculations on mononuclear and dinuclear model systems permit evaluation of both the structural distortions upon excitation to the lowest triplet excited state T(1) and the shape of the orbitals involved in the charge transfer transitions. These calculations also allow us to evaluate the influence of the substituent in position four of the benzenethiolate ligand and the presence of Au···Au interactions.     

Synthesis and antitumor activity of novel alkynyl (phosphine) digold(I) complexes

Transition Metal Chemistry - A series of 1,4-disubstituted digold–alkynyl complexes, [(PPh3)Au]2(μ-C≡C–Ar–CH≡C)], in which the 1,4-diethenylbenzene bridge...     

Cross-coupling reactions of gold(I) alkynyl and polyyndiyl complexes

Gold(I) alkynyl complexes are shown to efficiently couple with aryl iodides under mild conditions in the presence of both Pd(II) and Cu(I) co-catalysts. The reaction is not gold catalysed, but rather the Au(I) centre serves to transfer the alkynyl moiety to Cu(I), which then enters the conventional Sonogashira cycles. Using this method, a small range of 1,4-disubstituted diynes, including examples of differentially substituted compounds ArCCCCAr′, have been prepared directly from [(Ph₃P)AuCCCCAu(PPh₃)] and aryl iodides ArI.     

Use of phosphine gold acetylides [(R3P)AuCCR] to form phosphine gold derivatives of tetra-iron and penta-iron clusters

Five new gold acetylides, [AuCCR], with hydroxyl or amino functions in the organic radical R have been prepared. From these, nine phosphine complexes [(R₃P)AuCCR] with R = Ph or Cy were synthesised. Reactions between the phosphine gold acetylides [(Ph₃P)AuCCC(Me)(OH)Et] or [(Cy₃P)AuCCC(Me)(OH)Et] and the iron carbonyl cluster [Et₄N][Fe₄N(CO)₁₂] gave both neutral [(R₃P)AuFe₄N(CO)₁₂] and ionic compounds [(R₃P)₂Au][Fe₄N(CO)₁₂]. Reaction with the penta-iron cluster [Et₄N][Fe₅N(CO)₁₄] afforded [(R₃P)₂Au][Fe₅N(CO)₁₄], [(R₃P)₂Au][Fe₄N(CO)₁₂] and [(R₃P)AuFe₄N(CO)₁₂]. The gold-iron clusters were characterised with spectroscopic methods (IR, NMR and Mössbauer) and in the case of [(Cy₃P)AuFe₄N(CO)₁₂] a single-crystal X-ray analysis.     

Hexa- and octanuclear iron(III) salicylaldoxime clusters

The syntheses, structures and magnetic properties of six iron complexes stabilised with the derivatised salicylaldoxime ligands Me-saoH(2) (2-hydroxyethanone oxime) and Et-saoH(2) (2-hydroxypropiophenone oxime) are discussed. The four hexanuclear and two octanuclear complexes of formulae [Fe(8)O(2)(OMe)(4)(Me-sao)(6)Br(4)(py)(4)]·2Et(2)O·MeOH (1·2Et(2)O·MeOH), [Fe(8)O(2)(OMe)(3.85)(N(3))(4.15)(Me-sao)(6)(py)(2)] (2), [Fe(6)O(2)(O(2)CPh-4-NO(2))(4)(Me-sao)(2)(OMe)(4)Cl(2)(py)(2)] (3), [Fe(6)O(2)(O(2)CPh-4-NO(2))(4)(Et-sao)(2)(OMe)(4)Cl(2)(py)(2)]·2Et(2)O·MeOH (4·2Et(2)O·MeOH), [HNEt(3)](2)[Fe(6)O(2)(Me-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (5) and [HNEt(3)](2)[Fe(6)O(2)(Et-sao)(4)(SO(4))(2)(OMe)(4)(MeOH)(2)] (6) all are built from a series of edge-sharing [Fe(4)(μ(4)-O)](10+) tetrahedra. Complexes 1 and 2 display a new μ(4)-coordination mode of the oxime ligand and join a small group of Fe-phenolic oxime complexes with nuclearity greater than six.     

Aurophilicity in gold(I) thiosemicarbazone clusters

The reaction of the phosphine thiosemicarbazone ligands HLPH and HLPMe with Au(I) ions yields the gold complexes [Au(3)(HLPH)(2)Cl(2)]Cl·2MeOH (1·2MeOH) and [Au(2)(HLPMe)Cl(2)] (2). The structures determined by X Ray diffraction, [Au(3)(HLPH)(2)Cl(2)]Cl·4MeOH (1·4MeOH) and [Au(2)(HLPMe)Cl(2)](2) (2), are the first examples of gold(I) thiosemicarbazone clusters showing aurophilicity. The structure of the trinuclear cation 1 contains the Au(1) atom located in an inversion centre, being connected to another gold(I) atom, Au(2), through a phosphino thiosemicarbazone molecule which acts as a S,P-bridging ligand. Additionally, every gold(I) atom in the trinuclear cation 1 assembles into trinuclear linear cluster units by means of close gold-gold interactions, being connected through the crystal cell in a 2D zigzag mode. The crystal structure of [Au(2)(HLPMe)Cl(2)](2) (2) contains one discrete molecule [(AuCl)(2)(HLPMe)] in the asymmetric unit, which is further assembled into tetranuclear [(AuCl)(2)(HLPMe)](2) units by means of close gold-gold interactions. Both clusters are highly luminescent in solution.