Terpyridine isomerism as a tool for tuning red-to-NIR emissive properties in heteronuclear gold(I)-thallium(I) complexes

The polymeric linear chain [AuTl(C6Cl5)2]n reacts with three terpyridine-type ligands substituted with thiophene groups containing N-donor centres in different relative positions (L1, L2 and L3), leading to the Au(I)/Tl(I) complexes [AuTl(C6Cl5)2(L1)]n (1), [{AuTl(C6Cl5)2}2(L2)]n (2) and [AuTl(C6Cl5)2(L3)]n (3). X-Ray diffraction studies reveal that L1 acts as a chelate, while L2 and L3 act as bridging ligands, resulting in different coordination indexes for the thallium(I) centre. These structural differences strongly influence their optical properties, and while compounds 2 and 3 emit near the limit of the visible range, complex 1 emits in the infrared region. DFT calculations have also been carried out in order to determine the origin of the electronic transitions responsible for their optical properties.

Heteronuclear Gold(I)-Copper(I) Complexes with Thia- and Mixed Thia-Aza Macrocyclic Ligands: Synthesis, Structures and Optical Properties

The reactivity of the heterometallic polynuclear complexes [{Au(R)2 }2 Cu2 (MeCN)2 ]n (R=C6 F5 , C6 Cl5 ) with the thioether crowns 1,4,7-trithiacyclononane (L1, [12]aneS3 ), 1,4,8,11-tetrathiacyclododecane (L2, [14]aneS4 ), 1,4,7,10,13,16,19,22-octathiacyclotetracosane (L3, [24]aneS8 ), and the quinoline functionalized pendant arm derivatives of the 12-membered mixed-donor macrocycles 1-aza-,4,7,10-trithiacyclododecane ([12]aneNS3 ) and 1,7-diaza-4,10-dithiacyclododecane ([12]aneN2 S2 ), L4 and L5, respectively, was investigated in THF solution. While with L4 and L5 only ionic compounds of general formulation [Cu(L)][Au(R)2 ] were isolated and structurally characterized (none of them featuring Au⋅⋅⋅Cu interactions), with L1-L3, beside similar ionic compounds, some heteronuclear complexes of general formulation [{Au(R)2 }{Cu(L)}] and featuring Au⋅⋅⋅Cu interactions were also obtained. All of them display rather unusual non-classical C-H⋅⋅⋅Au hydrogen interactions. The complexes display in the solid state different optical properties related to their structures, which have been studied experimentally and theoretically via TD-DFT calculations. In particular, all compounds of the type [{Au(R)2 }{Cu(L)}] featuring Au⋅⋅⋅Cu metallophilic interactions display luminescence in the solid state both at room temperature (RT) and at 77 K. On the contrary, ionic compounds of general formulation [Cu(L)][Au(R)2 ], except [Cu(L4)][Au(C6 F5 )2 ], are not luminescent.

Vapochromic behaviour of a gold(I)-lead(II) complex as a VOC sensor

The reaction among [Au2Ag2(C6F5)4(OEt2)2]n, PbCl2 and terpyridine leads to the polymeric complex [{Au(C6F5)2}2{Pb(terpy)}]n (1). Its crystal structure reveals potential voids close to the lead centres large enough to hold different molecules. The availability of these free sites allows complex 1 to act as a VOC sensor. Thus, when 1 is exposed to different solvent vapours such as acetonitrile, toluene or THF, variations in its solid appearance and its photophysical properties are observed as a consequence of the formation of the new polymorphs [{Au(C6F5)2}2{Pb(terpy)(CH3CN)2}]n (2), [{Au(C6F5)2}2{Pb(terpy)}]n·Tol (3) and [{Au(C6F5)2}2{Pb(terpy)(THF)}]n·THF (4). Each polymorph displays a different emission energy depending on its structure and the presence of metallophilic interactions. In addition, the reversible solvent molecule exchange allows the tuning of the luminescence emissions in the greenish yellow-red range. DFT and TD-DFT calculations were performed to explain the origin of the luminescence of all these complexes.

Deciphering the Primary Role of Au⋅⋅⋅H-X Hydrogen Bonding in Gold Catalysis

Au⋅⋅⋅H-X (X=N or C) hydrogen bonding is gaining increasing interest, both in the study of its intrinsic nature and in their operability in different fields. While the role of these interactions has been studied in the stabilization of gold(I) complexes, their role during the minimum free energy reaction pathway of a given catalytic process remains unexplored. We report herein that complex [Au(C≡CPh)(pip)] (pip=piperidine) catalyses the A3 -coupling reaction for the synthesis of propargylamines, thanks to the ability of Au(I) to promote weak hydrogen bonding interactions with the reactants along the free energy profile. Density Functional Theory (DFT) calculations show that these Au⋅⋅⋅H-X interactions play a directing role in the catalysed A3 -coupling. Topological non-covalent interactions (NCI), interaction region indicator (IRI) and quantum theory of atoms in molecules (QTAIM) analysis in real space of the electron density provide a description of these interactions accurately.

Switching On/Off of a Solvent Coordination in a Au(I)-Pb(II) Complex: High Pressure and Temperature as External Stimuli

The benzonitrile solvate {[{Au(C6F5)2}2{Pb(terpy)}]·NCPh}n (1) (terpy = 2,2':6',2″-terpyridine) displays reversible reorientation and coordination of the benzonitrile molecule to lead upon external stimuli. High-pressure X-ray diffraction studies between 0 and 2.1 GPa reveal a 100% of conversion without loss of symmetry, which is totally reversible upon decompression. By variable-temperature X-ray diffraction studies between 100 and 285 K, a partial coordination is achieved.

Silver-based Terpyridine Complexes as Antitumor Agents

Silver complexes bearing substituted terpyridine or tetra-2-pyridinylpyrazine ligands have been prepared and structurally characterised. The study of the anticancer properties of silver complexes with this type of ligands is scarce, despite the possibilities of combining the properties of the metal and the ability of the ligands for DNA binding. Here, the antiproliferative activity, stability, CT-DNA binding and mechanism of cell death of these types of derivatives are studied. High cytotoxicity against different tumour cells was observed, and, more important, a great selectivity index has been detected between tumour cells and healthy Lymphocytes T for some of these compounds. The CT-DNA interaction study has shown that these derivatives are be able to interact with CT-DNA via moderate intercalation. Furthermore, cell death studies indicate that these derivatives promote the apoptosis via mitochondrial pathway.

A "gold standard" computational proof for the existence of gold(III) aurophilicity

The existence of aurophilic gold(III)⋯gold(III) interactions has for a long time been neglected due to structural arguments and comparison with the aurophilicity of gold(I) compounds. We show with calculations at the CCSD(T) level of theory that the [Au^III(CH₃)₃(NH₃)]₂ dimer has a metallophilic dispersion interaction between the gold(III) atoms of 10.5 kJ mol^-1. The aurophilic interaction is illustrated by topological QTAIM calculations and IRI analysis.

Spontaneous in situ generation of photoemissive aurophilic oligomers in water solution based on the 2-thiocytosine ligand

Complexes [Au(S-2-thiocytosinate)(PMe₃)] (2, 2-thiocytosine = 4-amino-2-mercaptopyrimidine) and [Au(S-2-thiocytosine)(PMe₃)](CF₃CO₂) (3) have been prepared by the reaction of [Au(acac)(PMe₃)] (1, acac = acetylacetonate) or [Au(OCOCF₃)(PMe₃)] with 2-thiocytosine, respectively. The equimolecular mixture of complexes 1 and 3 also produces [{Au(PMe₃)}₂(μ-S,N¹-2-thiocytosinate)](CF₃CO₂) (4), which features two distinct [Au(PMe₃)]⁺ groups coordinated to the S and N¹ atoms of the heterocycle. Complex 4 experiences a ligand redistribution process in water solution that liberates [Au(PMe₃)₂](CF₃CO₂) and a brightly coloured and luminescent species of [Au_n(μ-S,N¹-2-thiocytosinate)_n] stoichiometry, presumably as a tetraauracycle (n = 4).

The doubly-aurated [{Au(PMe₃)}₂(μ-S,N¹-2-thiocytosinate)]⁺ cation breaks up in water solution to form a strongly-coloured and photoluminescent neutral aurophilic oligomer.

Computational prediction of Au(I)-Pb(II) bonding in coordination complexes and study of the factors affecting the formation of Au(I)-E(II) (E = Ge, Sn, Pb) covalent bonds

We have studied computationally the Au-M (M = Ge, Sn, Pb) bonding trends in a series of model systems [(PH3)3Au-(MCl3)] (M = Ge (4), Sn (5), Pb (6)). For this, we have fully optimized the model systems at the MP2 level of theory, computing the Au-M bonding energy at the equilibrium distances applying the counterpoise (cp) correction to the basis-set superposition error (BSSE) and performing a natural energy decomposition analysis (NEDA). Furthermore, a topological analysis of the electron density using QTAIM, ELF and DORI tools was performed. In order to provide further insights on the possibility of predicting the existence of Au(i)-Pb(ii) donor bonds, Density Functional Theory calculations using the pbe functional and including dispersion corrections (DFT-D3/pbe) were performed on three model systems, [(PR3)3Au-(PbCl3)] (R = CH3 (7), H (8), CF3 (9)). This study also includes the corresponding NEDA calculations and the topological analysis of the electron density, which provides information about the Au-Pb bond, but also about the supporting weak ligand-ligand interactions. Overall, the study provides information about the factors affecting the formation of stabilizing Au(i)-Pb(ii) covalent bonds.

Time-Dependent Molecular Rearrangement of [Au(N9-adeninate)(PTA)] in Aqueous Solution and Aggregation-Induced Emission in a Hydrogel Matrix

An in-depth study of the molecular rearrangement of the complex [Au(N⁹-adeninate)(PTA)] (1), promoted in aqueous solution, is presented. This complex, which has been previously described as forming dimers in its crystalline form, is also demonstrated as being able to assemble into an infinite Au^I···Au^I chain polymer. The structural motifs are tentatively related to the dramatic modification of the photoemissive properties of 1 in water solution at long times, with the aid of UV-vis and photoluminescence measurements, PGSE-NMR, and theoretical calculations. A subtle equilibrium in favor of aurophilically governed aggregates has been envisaged as the driving force of the molecular rearrangement. Furthermore, 1 has been explored as an additive of the hydrogel of [Au(N⁹-adeninate)(PMe₃)] (2) for a further tuning of its photophysical properties without loss of the gel texture.

Multidisciplinary study on the hydrogelation of the digold(i) complex [{Au(9N-adeninate)}2(μ-dmpe)]: optical, rheological, and quasi-elastic neutron scattering perspectives

Non-conventional experimental techniques such as rheology or QENS will aid synthetic inorganic chemists to broaden the knowledge on gold(i) hydrometallogels’ structure and properties and to understand their expected relationship.

An improved plasmonic Au–Ag/TiO2/rGO photocatalyst through entire visible range absorption, charge separation and high adsorption ability

Plasmonic nanohybrids for visible light absorption: the combination of small alloyed AuAg NPs, TiO₂ NPs and rGO nanosheets provides wide visible light absorption improving the photocatalytic efficiency towards water pollutant remediation.

Perhalophenyl Three-Coordinate Gold(I) Complexes as TADF Emitters: A Photophysical Study from Experimental and Computational Viewpoints

We report the synthesis of novel perhalophenyl three-coordinated gold(I) complexes using 1,2-bis(diphenylphosphino)benzene (dppBz) as the chelating ligand and [AuR(tht)] (R = C₆F₅, C₆Cl₂F₃, C₆Cl₅) as the perhalophenyl-gold(I) source, leading to [AuR(dppBz)] (R = C₆F₅ (1), C₆Cl₂F₃ (2), C₆Cl₅ (3)) complexes. The solid-state structures of compounds 2 and 3 consist of discrete three-coordinated Au(I) complexes, which show a distorted trigonal planar geometry for the gold center with dissimilar Au-P distances. The distorted structural arrangement is closely related to its photophysical properties. The studied complexes display very intense emissions at room temperature (RT) and at 77 K in the solid state. Studies of the emissive properties of the complexes at different temperatures suggest that the emissions are phosphorescent at 77 K and exhibit thermally activated delayed fluorescence (TADF) at RT. First-principle calculations of the photophysical processes yielded rate constants for intersystem crossing and reverse intersystem crossing that are in excellent agreement with experimental data.

Metallophilic Au(i)⋯M(i) interactions (M = Tl, Ag) in heteronuclear complexes with 1,4,7-triazacyclononane: structural features and optical properties

New heterometallic Au(i)–M (M = Ag(i) or Tl(i)) complexes show macrocylic ligand (TACN)-directed emissive properties.

Temperature-assisted formation of reversible metallophilic Au-Ag interaction arrays

A temperature-controlled self-assembly process in a solution of [Ag(terpy)]nn+ and [Au(C6F5)2]- units has been performed. For this, the crystallisation of the complex [{Au(C6F5)2}Ag(terpy)]n under the same experimental conditions, changing only the temperature, allows the synthesis of polymorphs [{Au(C6F5)2}2Ag2(terpy)2]n (2a) at 298 K and [{Au(C6F5)2}Ag(terpy)]n (2b) at 280 K. The X-ray diffraction studies previously reported for 2a revealed a polymeric structure with an unusual + + - - + + - - charge sequence, whereas for polymorph 2b, a more classical + - + - disposition has been obtained. The conversion of one polymorph into the other can be achieved by simple dissolution of one of them and by recrystallisation at the corresponding temperature. The mechanism of the formation of each polymorph is proposed in view of their 1H NMR, 1H-PGSE NMR and molar conductivity measurements.

Balancing ionic and H-bonding interactions for the formation of Au(i) hydrometallogels

Complex [Au(⁹N-adenine)(PMe₃)](CF₃CO₂) displays a supramolecular structure built up through ionic, π-stacking, C–H⋯O, C–H⋯N and C–H⋯Au interactions. This complex forms a stable hydrometallogel consisting of straight molecular nanowires.

Unequal coordination environment in complexes of the type [Au2Ag2(R)4(L)2]n. An immiscible solvent mixture as a key point in the control of ligand replacement

Following an acid-base strategy, based on the reaction between gold(i) basic fragments and acid silver salts, it is possible to obtain heterometallic polymers of the general formula [Au₂Ag₂(R)₄(L)₂]_n (R = C₆Cl₂F₃; L = pyrimidine). Using this new heterometallic complex [Au₂Ag₂(C₆Cl₂F₃)₄(pym)₂]_n (1) as a starting material, and a good coordinating solvent such as acetonitrile, it is possible to modify the arrangement of the ligands connected to the silver centres and to obtain three different tetranuclear Au₂Ag₂ building blocks leading to the new polymer [Au₆Ag₆(C₆Cl₂F₃)₁₂(μ₂-pym)₂(NCMe)₆]_n (2). Both complexes display very intense luminescence emission. Structural, experimental and computational studies have been carried out in order to identify the origin of these properties and the factors that can affect them, such as, the presence of metallophilic interactions as well as different coordination environments for the metallic centres.

Lead encapsulation by a golden clamp through multiple electrostatic, metallophilic, hydrogen bonding and weak interactions

Complex [{Pb(HBpz₃)}{Au₃(o-C₆BrF₄)₃(HBpz₃)}] consists of a host–guest heterometallic system built up through a plethora of interactions including ionic and dispersive forces.

Polarized Supramolecular Aggregates Based on Luminescent Perhalogenated Gold Derivatives

The reaction of [Au(C₆F₅)(tht)] (tht = tetrahydrothiophene) with 1,3,5-triaza-7-phosphaadamantane (PTA) and 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) leads to the formation of [Au(C₆F₅)(phosph)] (phosph = PTA, 1; phosph = DAPTA, 2). The compounds are slightly soluble in water and aggregate at higher concentrations, giving rise to the formation of needle- and rodlike structures (1) and well-organized spherical aggregates (2). Compounds 1 and 2 were reacted with AgPF₆, giving rise to the formation in all cases of luminescent water-soluble 1:1 Au···Ag heterometallic complexes, as evidenced by X-ray crystal structure determination. The use of different silver salts that differ on the counterion induces changes in the resulting luminescence and aggregation morphology.

New Au(i)–Cu(i) heterometallic complexes: the role of bridging pyridazine ligands in the presence of unsupported metallophilic interactions

The use of N-donor pyridazine ligands in different amounts in the reaction with a Au(i)/Cu(i) precursor allows the control of metallophilic interactions in the solid state.

Luminescent aryl–group eleven metal complexes

This perspective highlights the recent developments in the study of the photoluminescent properties of aryl–group eleven complexes. Related properties and applications such as electroluminescence, triboluminescence, mechanochromism, luminescent liquid crystals, low molecular weight gelators and photocatalysts are also discussed.

Tuning the Luminescent Properties of a Ag/Au Tetranuclear Complex Featuring Metallophilic Interactions via Solvent-Dependent Structural Isomerization

In this paper the reaction products of the basic gold(I) species [Au(C₆Cl₅)₂]^- against the acid salt Ag(OClO₃) in the presence of the S-donor macrocyclic ligand 1,4,7-trithiacyclononane ([9]aneS₃) are studied in different solvents. Two different isomers of stoichiometry [{Au(C₆Cl₅)₂}Ag([9]aneS₃)]₂ were isolated depending on the solvent used, dichloromethane or tetrahydrofuran, which show different luminescence in the solid state. X-ray diffraction studies of these compounds reveals that both show the same heteropolynuclear Ag···Au···Au···Ag system but with different Au···Au interaction distances and different relative positions of the cationic fragment [Ag([9]aneS₃)]⁺ in the structure with respect the bimetallic Au···Au core. This work includes a study of the optical properties of both isomers, as well as time-dependent density functional theory calculations that were performed to determine the origin of their different luminescence.

Double Jahn-Teller Distortion in AuGe Complexes Leading to a Dual Blue-Orange Emission

Invited for this month's cover are collaborators from the group of José M. López-de-Luzuriaga at Universidad de la Rioja, Spain and researchers from University of Helsinki, Finland. The cover picture shows a photograph of a gold-germanium complex that has two emission modes corresponding to two independent triplet excited states. Read the full text of the article at 10.1002/cplu.201500337.

Synthesis of the molecular amalgam [{AuHg2(o-C6F4)3}{Hg3(o-C6F4)3}]−: a rare example of a heterometallic homoleptic metallacycle

The formation of [Au(PMe₃)₂][{AuHg₂(o-C₆F₄)₃}{Hg₃(o-C₆F₄)₃}] by a gold mercury transmetalation mechanism is reported. The complex shows very short Au(i)–Hg(ii) contacts. Theoretical calculations indicate an extremely strong metallophilic interaction.

Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2':6',2"-Terpyridine Ligand Framework

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2':6',2"-terpyridine (terpy) leads to complex [Au(C6F5)(η(1)-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η(3)-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2.

The spontaneous formation and plasmonic properties of ultrathin gold-silver nanorods and nanowires stabilized in oleic acid

Ultrathin Au-Ag alloy nanorods and nanowires of different lengths and ca. 1.9 nm diameter are prepared through a low-temperature decomposition of the precursor [Au2Ag2(C6F5)4(OEt2)2]n in oleic acid. This nanostructure formation has been studied through TEM, HRTEM, EDS, HS-SPME-GC-MS and (19)F NMR spectroscopy. The UNRs and UNWs display a length-dependent broad band in the mid-IR region that is related to the longitudinal mode of the surface plasmon resonance of the ultrathin nanostructures.

Ultrasmall NHC-coated gold nanoparticles obtained through solvent free thermolysis of organometallic Au(i) complexes

Ultrasmall gold nanoparticles (Au UNPs) represent a unique class of nanomaterials making them very attractive for certain applications. Herein, we developed an organometallic approach to the synthesis of Au UNPs stabilized with the C18H37-NHC ligand by the solvent free thermolysis of [RMIM][Au(C6F5)2] () or [Au(C6F5)(RNHC)] () (with R = C18H37-), by controlling the reactivity of pentafluorophenyl ligands as deprotonating or reductive elimination agents; Au UNPs can be achieved by solvent free thermolysis. Pentafluorophenyl Au(i) complexes and are synthesized from the corresponding ionic and neutral precursors. The presence of long alkyl chain imidazolium or carbene species in the complexes makes them to behave as isotropic liquids at moderate temperatures. The use of multinuclear NMR allows the description of the mechanism of formation of the UNPs as well as the surface state of the UNPs.

1,4-Bis(2'-pyridylethynyl)benzene as a ligand in heteronuclear gold-thallium complexes. Influence of the ancillary ligands on their optical properties

The reaction of 1,4-bis(2'-pyridylethynyl)benzene (L) with [{Au(C6X5)2}Tl]n affords new heterometallic Au(I)/Tl(I) complexes with different stoichiometries, structural arrangements and optical properties depending on the halogens present in the aryl group. The chlorinated derivative [{Au(C6Cl5)2}Tl(L)]n () displays polymeric chains built thanks to unsupported AuTl interactions and bridging bidentate ligands between adjacent chains, while in the fluorinated species [{Au(C6F5)2}2Tl2(L)2]n (), also containing N-donor bridging ligands and AuTl contacts, polymerization occurs via TlCaryl non-bonding interactions between neighbouring molecules. The optical properties of and have been studied experimentally and theoretically, concluding that the luminescence of in the solid state has its origin in the AuTl interactions, and that the TlCaryl interactions in favour a non-radiative deactivation pathway that avoids luminescence. The strength of the non-bonding interactions present in has also been theoretically studied at the HF and MP2 levels, revealing the metallophilic contact as the strongest one.

The effect of gold(i) coordination on the dual fluorescence of 4-(dimethylamino)pyridine

Coordination of 4-(dimethylamino)pyridine to perhalophenyl gold(i) fragments leads to the formation of novel fluorescent complexes, in which the photophysical properties of the ligand are greatly influenced by the polarity induced by the organometallic fragment.

The gold(i)···lead(ii) interaction: a relativistic connection

The crystal structure of complex [Pb{HB(pz)₃}Au(C₆Cl₅)₂] 1 displays an unsupported Au(i)···Pb(ii) interaction. This complex emits at 480 nm in the solid state due to an aurate(i) to lead(ii) charge transfer, in which the existence of a metallophilic interaction is a pre-requisite. Ab initio calculations show a very strong Au(i)···Pb(ii) closed-shell interaction of -390 kJ mol^-1, which has an ionic plus a dispersive (van der Waals) nature strengthened by large relativistic effects (>17%).