Gold-gold interactions as crystal engineering design elements in heterobimetallic coordination polymers

Unusually short unsupported Au(III)⋯Au(III) aurophilic contacts in emissive lanthanide tetracyanoaurate(III) complexes

A series of [Au(CN)4]- salts with lanthanide 2,2'-bipyridine dioxide cations features Au(III) aurophilic interactions between [Au(CN)4]- groups, with Au⋯Au distances of 3.3603(4) Å and 3.4354(4) Å that are shorter than any previously reported. Computations predict the interactions to be weakly attractive; packing effects appear to also contribute to the close contacts. The materials are emissive: there is no Au(III)-based luminescence, but for Ln = Eu the PLQY of 29% is surprisingly high compared to related analogues.

Metallophilic interactions in silver(I) dicyanoaurate complexes

This manuscript reports four new gold(I)−silver(I) complexes with 2-(2-pyridyl)-1,8-naphthyridine (pyNP) and terpyridine (terpy) as ancillary ligands, of formulation [Ag(pyNP)(Au(CN)2)]2 (1), [Ag2Au2(μ-CN)2(CN)2(pyNP)2] (2), [Ag2Au(μ-CN)2(terpy)2][Au(CN)2] (3) and [Ag4Au4(μ-CN)8(terpy)2(py)] (4). Complexes 1 and...

Molecular gold strings: aurophilicity, luminescence and structure-property correlations

This review covers the compound class of one-dimensional gold strings. These compounds feature a formally infinite repetition of gold complexes as monomers/repeating units that are held together by aurophilic interactions, i.e. direct gold-gold contacts. Their molecular structures are primarily determined in the solid state using single crystal X-ray diffraction. The chemical composition of the employed gold complexes is diverse and furthermore plays a key role in terms of structure characteristics and the resulting properties. One of the most common features of gold strings is their photoluminescence upon UV excitation. The emission energy is often dependent on the distance of adjacent gold ions and the electronic structure of the whole string. In terms of gold strings, these parameters can be fine-tuned by external stimuli such as solvent, pH value, pressure or mechanical stress. This leads to direct structure-property correlations, not only with regard to the photophysical properties, but also electric conductivity for potential application in nanoelectronics. Concerning these correlations, gold strings, consisting of self-assembled individual complexes as building blocks, are the ideal compound class to look at, as perturbations by an inhomogeneity in the ligand sphere (such as the end of a molecule) can be neglected. Therefore, the aim of this review is to shed light on the past achievements and current developments in this area.

Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions

Excimers and exciplexes are defined as assemblies of atoms or molecules A/A' where interatomic/intermolecular bonding appears only in excited states such as [A2 ]* (for excimers) and [AA']* (for exciplexes). Their formation has become widely known because of their role in gas-phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI (5d10 )) through aurophilic contacts. In the corresponding excimers, a new type of Au⋅⋅⋅Au bonding arises, with bond energies and lengths approaching those of ground-state Au-Au bonds between metal atoms in the Au0 (5d10 6s1 ) and AuII (5d9 ) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.

Understanding the vapochromic response of mixed copper(i) iodide/silver(i) Iodide nanoparticles toward dimethyl sulfide

We report on the vapochromic behavior of a series of homo- and heterometallic copper(i) iodide/silver(i) iodide nanoparticles when exposed to dimethyl sulfide (DMS) vapor. These systems show remarkable colorimetric sensing behavior via emission color upon DMS exposure, shifting from pink to green emission. Kinetics measurements of CuI/AgI nanoparticle reactions with DMS show a significant rate increase with increasing Ag(i) content. However, luminescence spectroscopy and X-ray diffraction of the post-exposure samples with varying Ag(i) content reveal that the luminophore is identical in all cases and contains no Ag(i) ions. To rationalize the experimental observations and determine the vapochromic response mechanism, molecular dynamic calculations were performed on model (111) cation-terminated surfaces of copper iodide crystals doped with variable amounts of silver. Computational studies indicate that heterometallic Cu/Ag systems have a stronger binding affinity towards DMS vapor molecules than homometallic CuI and that embedding of the DMS molecules into the surface is the primary intermediate by which the vapochromic response occurs.

Synthesis, characterization and anticancer activity in vitro evaluation of novel dicyanoaurate (I)-based complexes

Molecular structures containing gold, such as auranofin, have been extensively studied in the diagnosis and treatment of many diseases, including cancer treatment. The pharmacological properties of the newly synthesized unique gold-ligand structures have been reported for different cancer cell lines. However, findings on bishydeten-metal salt complexes with gold are rare. In this work, the synthesis of five novel cyanide-bridged coordination compounds having the closed formulae [Ni(bishydeten)][Au(CN)₂]₂ (1), [Cu(bishydeten)][Au(CN)₂]₂ (2), [Zn(bishydeten)₂Au₃(CN)₄][Au₂(CN)₃] (3), [Cd(bishydeten)_0,5]₂[Au(CN)₂]₄.2H₂O (4), and [Cd(bishydeten)₂][Au(CN)₂]₂ (5) (where bisyhdeten = N,N-bis(2-hydroxyethyl)ethylene diamine), and their characterization by elemental, infrared, ESI-MS, X-ray (for 2) and thermic measurement methods were performed. Complexes 1 and 3 are thermally more stable than the other three complexes. For these, pharmacological adequacies were also tested. The nucleic acid and protein binding affinities of the Au (I) compounds were also estimated by spectroscopic and electrophoretic techniques. Au (I) complexes were identified as strong chemotherapeutic with mild cytotoxicity, and they demonstrated a dose-dependent inhibition on the growth of cancer cells with IC50 at 0.11 to 0.47 μM. Investigation of mechanisms of action on cells revealed that Au (I) compounds managed to inhibit cell migration and led to a decrease in cytoskeletal proteins such as CK7 and CK20. However, Au (I) compounds failed to inhibit DNA topoisomerase I. Overall, and we suggest that potent antiproliferative activity, mild cytotoxicity, good solubility, and micromolar dosage of Au (I) compounds containing bisyhdeten-metal derivatives render them the potential focus of further studies as chemotherapeutic agents.

Synthesis, structure and photophysical properties of a 2D network with gold dicyanide donors coordinated to aza[5]helicene viologen acceptors

Investigation of a gold-heli viologen network shows the presence of [Au(CN)₂]⁻ dimers and monomers within the 2D framework, and quenching of the [Au(CN)₂]⁻ luminescence by the helicene.

The interplay of non-covalent interactions determining the antiparallel conformation of (isocyanide)gold(i) dimers

Ligand⋯ligand contacts, including a novel n → π* interaction involving an isocyanide group as the acceptor, determine the persistent antiparallel conformation of dimers of (isocyanide)Au(i) complexes in their crystal structures.

In(iii)⋯In(iii) short contacts: an unnoticed metallophilic interaction?

We report here the existence of particularly close contacts between In(iii) centres in the crystals of Lewis acid–base adducts that show features of d¹⁰⋯d¹⁰ closed-shell metallophilic interactions.

Synthesis and crystal structure of a 3D copper(II)–silver(I) coordination polymer assembled through hydrogen bonding, π–π stacking and metal–π interactions, {[Cu(phen)2(CN)][Ag(CN)2] · 3H2O} n (phen = 1,10-phenanthroline)

A copper(II) polymeric complex {[Cu(phen)2(CN)][Ag(CN)2] · 3H2O} n , 1 (phen = 1,10-phenanthroline), has been prepared and structurally characterized. The compound crystallizes in the monoclinic space group P21/c with [Cu(phen)2(CN)]+ and [Ag(CN)2]− units and three water molecules. The cationic and anionic units are linked to each other through M-π and π–π interactions. The array is extended further by hydrogen bonding and π–π interactions to form a 3D network.

Five novel dicyanidoaurate(i)-based complexes exhibiting significant biological activities: synthesis, characterization and three crystal structures

Herein the anticancer, antibacterial, and antifungal effects of the five novel dicyanidoaurate(i)-based complexes have been reported.

Synthesis and characterization of two novel dicyanidoargentate(i) complexes containing N-(2-hydroxyethyl)ethylenediamine exhibiting significant biological activity

Two novel cyanido-complexes having very significant antibacterial, antifungal and anticancer activities in vitro were synthesized and characterized using various techniques.

Coordination assembly of Borromean structures

The state-of-art advances in the assembly of coordination supramolecular structures featuring Borromean topological character have been introduced.

The gold-hydrogen bond, Au-H, and the hydrogen bond to gold, Au∙∙∙H-X

In the first part of this review, the characteristics of Au-H bonds in gold hydrides are reviewed including the data of recently prepared stable organometallic complexes with gold(I) and gold(III) centers. In the second part, the reports are summarized where authors have tried to provide evidence for hydrogen bonds to gold of the type Au∙∙∙H-X. Such interactions have been proposed for gold atoms in the Au(-I), Au(0), Au(I), and Au(III) oxidation states as hydrogen bonding acceptors and H-X units with X = O, N, C as donors, based on both experimental and quantum chemistry studies. To complement these findings, the literature was screened for examples with similar molecular geometries, for which such bonding has not yet been considered. In the discussion of the results, the recently issued IUPAC definitions of hydrogen bonding and the currently accepted description of agostic interactions have been used as guidelines to rank the Au∙∙∙H-X interactions in this broad range of weak chemical bonding. From the available data it appears that all the intra- and intermolecular Au∙∙∙H-X contacts are associated with very low binding energies and non-specific directionality. To date, the energetics have not been estimated, because there are no thermochemical and very limited IR/Raman and temperature-dependent NMR data that can be used as reliable references. Where conspicuous structural or spectroscopic effects have been observed, explanations other than hydrogen bonding Au∙∙∙H-X can also be advanced in most cases. Although numerous examples of short Au∙∙∙H-X contacts exist in the literature, it seems, at this stage, that these probably make only very minor contributions to the energy of a given system and have only a marginal influence on molecular conformations which so far have most often attracted researchers to this topic. Further, more dedicated investigations will be necessary before well founded conclusions can be drawn.

Vapochromic behaviour of M[Au(CN)2]2-based coordination polymers (M = Co, Ni)

A series of M[Au(CN)₂]₂(analyte)_x coordination polymers (M = Co, Ni; analyte = dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), pyridine; x = 2 or 4) was prepared and characterized. Addition of analyte vapours to solid M(μ-OH₂)[Au(CN)₂]₂ yielded visible vapochromic responses for M = Co but not M = Ni; the IR ν_CN spectral region changed in every case. A single crystal structure of Zn[Au(CN)₂]₂(DMSO)₂ revealed a corrugated 2-D layer structure with cis-DMSO units. Reacting a Ni(II) salt and K[Au(CN)₂] in DMSO yielded the isostructural Ni[Au(CN)₂]₂(DMSO)₂ product. Co[Au(CN)₂]₂(DMSO)₂ and M[Au(CN)₂]₂(DMF)₂ (M = Co, Ni) complexes have flat 2-D square-grid layer structures with trans-bound DMSO or DMF units; they are formed via vapour absorption by solid M(μ-OH₂)[Au(CN)₂]₂ and from DMSO or DMF solution synthesis. Co[Au(CN)₂]₂(pyridine)₄ is generated via vapour absorption by Co(μ-OH₂)[Au(CN)₂]₂; the analogous Ni complex is synthesized by immersion of Ni(μ-OH₂)[Au(CN)₂]₂ in 4% aqueous pyridine. Similar immersion of Co(μ-OH₂)[Au(CN)₂]₂ yielded Co[Au(CN)₂]₂(pyridine)₂, which has a flat 2-D square-grid structure with trans-pyridine units. Absorption of pyridine vapour by solid Ni(μ-OH₂)[Au(CN)₂]₂ was incomplete, generating a mixture of pyridine-bound complexes. Analyte-free Co[Au(CN)₂]₂ was prepared by dehydration of Co(μ-OH₂)[Au(CN)₂]₂ at 145 °C; it has a 3-D diamondoid-type structure and absorbs DMSO, DMF and pyridine to give the same materials as by vapour absorption from the hydrate.

Changes in electronic properties of polymeric one-dimensional {[M(CN)2]-}n (M = Au, Ag) chains due to neighboring closed-shell Zn(II) or open-shell Cu(II) ions

A series of d(10) dicyanometallate polymeric compounds were studied by electronic spectroscopy and density functional theory (DFT) calculations. In these materials, the negatively charged one-dimensional (1D) polymeric chains are linked together by [M(en)(2)](2+) (M = Cu(II) and Zn(II); en = ethylenediamine). More than innocent building blocks, the [M(en)(2)](2+) units offer a possible synthetic way to modify electronic properties of the materials. Through its low energy d-d excited state, the d(9) copper(II) ions offer deactivation pathways for the normally emissive dicyanometallate polymer. Deactivation was shown to be specific to the excited state energy.