Structural, Photophysical, and Catalytic Properties of Au(I) Complexes with 4-Substituted Pyridines

A novel approach for estimating the strength of argentophilic and aurophilic interactions using QTAIM parameters

Metallophilic interactions, specifically argentophilic (Ag⋯Ag) and aurophilic (Au⋯Au) interactions, play a crucial role in stabilizing various molecular and solid-state structures. In this manuscript, we present a convenient method to estimate the strength of argentophilic and aurophilic interactions based on quantum theory of atoms in molecules (QTAIM) parameters evaluated at the bond critical points connecting the metal centres. We employ density functional theory (DFT) calculations and the QTAIM parameters to develop this energy predictor. To validate the reliability and applicability of our method, we test it using a selection of X-ray crystal structures extracted from the cambridge structural database (CSD), where argentophilic and aurophilic interactions are known to be significant in their solid-state arrangements. This method offers a distinct advantage in systems where multiple interactions, beyond metallophilic interactions, contribute to the overall stability of the structure. By employing our approach, researchers can distinctly quantify the strength of argentophilic and aurophilic interactions, facilitating a deeper understanding of their impact on molecular and solid-state properties. This method fills a critical gap in the existing literature, offering a valuable tool to researchers seeking to unravel the intricate interactions in metal-containing compounds.

Crystal structures of four gold(I) complexes [AuL 2]+[AuX 2]- and a by-product (L·LH+)[AuBr2]- (L = substituted pyridine, X = Cl or Br)

Bis(2-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C6H7N)2][AuBr2], (1), crystallizes in space group C2/c with Z = 4. Both gold atoms lie on twofold axes and are connected by an aurophilic contact. A second aurophilic contact leads to infinite chains of alternating cations and anions parallel to the b axis, and the residues are further connected by a short H⋯Au contact and a borderline Br⋯Br contact. Bis(3-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C6H7N)2][AuBr2], (2), crystallizes in space group C2/m with Z = 2. Both gold atoms lie on special positions with symmetry 2/m and are connected by an aurophilic contact; all other atoms except for one methyl hydrogen lie in mirror planes. The extended structure is closely analogous to that of 1, although the structures are formally not isotypic. Bis(3,5-di-methyl-pyridine)-gold(I) di-chlor-ido-aurate(I), [Au(C7H9N)2][AuCl2], (3) crystallizes in space group P with Z = 2. The cation lies on a general position, and there are two independent anions in which the gold atoms lie on inversion centres. The cation and one anion associate via three short H⋯Cl contacts to form a ribbon structure parallel to the b axis; aurophilic contacts link adjacent ribbons. Bis(3,5-di-methyl-pyridine)-gold(I) di-bromido-aurate(I), [Au(C7H9N)2][AuBr2], (4) is isotypic to 3. Attempts to make similar compounds involving 2-bromo-pyridine led instead to 2-bromopyridinium di-bromido-aurate(I)-2-bromo-pyridine (1/1), (C5H5BrN)[AuBr2]·C5H4BrN, (5), which crystallizes in space group P with Z = 2; all atoms lie on general positions. The 2-bromo-pyridinium cation is linked to the 2-bromo-pyridine mol-ecule by an N-H⋯N hydrogen bond. Two formula units aggregate to form inversion-symmetric dimers involving Br⋯Br, Au⋯Br and H⋯Br contacts.

Pyridine Iodine(I) Cations: Kinetic Trapping as a Sulfonate Complexes

Seven pyridine iodine(I) sulfonate complexes were prepared and isolated at low temperatures and characterized by X-ray diffraction analysis. The inherently instable pyridine iodine(I) cations are stabilized by an oxygen of sulfonate anions via the I⋅⋅⋅O halogen bond. In these complexes, the iodine atom of the pyridine iodine(I) cation acts as an electron acceptor and the sulfonate oxygen as the electron donor. These complexes are stable enough in the crystalline state, yet decompose rapidly under ambient conditions, also being unstable in solution. The (pyridine)N-I bond lengths [2.140(3)-2.197(2) Å] and the I⋅⋅⋅O halogen bonds [2.345(6)-2.227(3) Å] are analogous to (imide)N-I⋅⋅⋅O-N-pyridine uncharged halogen-bonded complexes formed from N-haloimides and pyridine N-oxides, thus confirming the existence of elusive pyridine iodine(I) cation.

Luminescence and Length Control in Nonchelated d 8 ‐Metallosupramolecular Polymers through Metal‐Metal Interactions

Supramolecular polymers (SPs) of d⁸ transition metal complexes have received considerable attention by virtue of their rich photophysical properties arising from metal‐metal interactions. However, thus far, the molecular design is restricted to complexes with chelating ligands due to their advantageous preorganization and strong ligand fields. Herein, we demonstrate unique pathway‐controllable metal‐metal‐interactions and remarkable ³MMLCT luminescence in SPs of a non‐chelated Pt^II complex. Under kinetic control, self‐complementary bisamide H‐bonding motifs induce a rapid self‐assembly into non‐emissive H‐type aggregates (1A). However, under thermodynamic conditions, a more efficient ligand coplanarization leads to superiorly stabilized SP 1B with extended Pt⋅⋅⋅Pt interactions and remarkably long ³MMLCT luminescence (τ^77 K=0.26 ms). The metal‐metal interactions could be subsequently exploited to control the length of the emissive SPs using the seeded‐growth approach.

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.

Coordination-Driven Self-Assembly of Silver(I) and Gold(I) Rings: Synthesis, Characterization, and Photophysical Studies

In this work, we investigate the self-assembly between Ag(I) and Au(I) centers and pyridyl donors to form hexagonal metallacycles and related linear complexes. The precipitation of hexagonal metallacycles upon assembly in chloroform/methanol mixtures results in high solid-state photo-stability. Whereas, the Ag(I) species have fast kinetics and high formation constants in acetone, this solvent interferes in the formation of the analogous Au(I) complexes. The photophysical properties of this suite of metallacycles was investigated including steady-state absorption, emission, and time-resolved lifetime measurements. All ligands and hexagons exhibited ligand-centered singlet emissions with ground-state absorption and emission perturbed upon coordination. The ligand-based fluorescent photoluminescence was affected by the heavy-atom effect when halide or metals are present, attenuating quantum yields as evidenced by increases in the experimentally measured non-radiative rate constants. The formation of group 11 metallacycles is motivated by their potential applications in mixed-matrix materials wherein metal ions can interact with substrate to facilitate separations chemistry with reduced energy requirements, in particular the isolation of ethylene and light olefins. Existing processes involve cryogenic distillation, an energy intensive and inefficient method.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Of all divalent metals, mercury (HgII ) has the highest affinity for metallothioneins. HgII is considered to be enclosed in the α and β domains as tetrahedral α-type Hg4 Cys11-12 and β-type Hg3 Cys9 clusters similar to CdII and ZnII . However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the HgII partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (β-HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

Emissive Azobenzenes Delivered on a Silver Coordination Polymer

Azobenzene has become a ubiquitous component of functional molecules and polymeric materials because of the light-induced trans → cis isomerization of the diazene group. In contrast, there are very few applications utilizing azobenzene luminescence, since the excitation energy typically dissipates via nonradiative pathways. Inspired by our earlier studies with 2,2'-bis[ N,N'-(2-pyridyl)methyl]diaminoazobenzene (AzoAM oP) and related compounds, we investigated a series of five aminoazobenzene derivatives and their corresponding silver complexes. Four of the aminoazobenzene ligands, which exhibit no emission under ambient conditions, form silver coordination polymers that are luminescent at room temperature. AzoAE pP (2,2'-bis[ N,N'-(4-pyridyl)ethyl]diaminoazobenzene) assembles into a three-dimensional coordination polymer (AgAAE pP) that undergoes a reversible loss of emission upon the addition of metal-coordinating analytes such as pyridine. The switching behavior is consistent with the disassembly and reassembly of the coordination polymer driven by displacement of the aminoazobenzene ligands by coordinating analytes.

Well defined difluorogold(iii) complexes supported by N-ligands

Rare difluorogold(iii) complexes supported by N-ligands can be synthesized simply either from Au(i) precursors using XeF₂ or Au(iii) using KF.

Access to the Parent Tetrakis(pyridine)gold(III) Trication, Facile Formation of Rare Au(III) Terminal Hydroxides, and Preliminary Studies of Biological Properties

In this paper we report on the use of [NO][BF4] to access tricationic tetrakis(pyridine)gold(III) from Au powder, a species inaccessible using the more traditional (tetrahydrothiophene)AuCl route. It is then demonstrated that this family of compounds can be used to access new terminal Au(III) hydroxides, a challenging class of compounds, and the first crystallographically characterized examples employing bidentate ligands. Finally, preliminary biological studies indicate good activity for derivatives featuring polydentate ligands against the HeLa and PC3 cell lines but also strong inhibition of primary HUVEC cells.

Weaving an infinite 3-D supramolecular network via AuI⋯AuIII aurophilicity and C–H⋯Cl hydrogen bonding

The use of ligand-unsupported Au^I⋯Au^III interactions to increase the structural dimensionality to a 3-D array was demonstrated.

Bis(4-picoline-κN)gold(I) dibromidoaurate(I) and bis(4-picoline-κN)gold(I) dichloridoaurate(I): space-group ambiguity?

Bis(4-picoline-κN)gold(I) dibromidoaurate(I), [Au(C6H7N)2][AuBr2], (I), crystallizes in the monoclinic space group P21/n, with two half cations and one general anion in the asymmetric unit. The cations, located on centres of inversion, assemble to form chains parallel to the a axis, but there are no significant contacts between the cations. Cohesion is provided by flanking anions, which are connected to the cations by short Au···Au contacts and C-H···Br hydrogen bonds, and to each other by Br···Br contacts. The corresponding chloride derivative, [Au(C6H7N)2][AuCl2], (II), is isotypic. A previous structure determination of (II), reported in the space group P1 with very similar axis lengths to those of (I) [Lin et al. (2008). Inorg. Chem. 47, 2543-2551], might be identical to the structure presented here, except that its γ angle of 88.79 (7)° seems to rule out a monoclinic cell. No phase transformation of (II) could be detected on the basis of data sets recorded at 100, 200 and 295 K.

Arylsilanes: application to gold-catalyzed oxyarylation of alkenes

Arylsilanes are efficient reagents for the gold-catalyzed oxyarylation of alkenes (21 examples, up to 85% isolated yield). Using commercially available Ph(3)PAuCl and readily prepared, benign arylsilanes, these two- and three-component reactions proceed smoothly in air. The oxidant, Selectfluor, not only facilitates entry to the Au(I/III) manifold but also provides a fluoride anion for silane activation, thereby avoiding the need for addition of a stoichiometric base.

1H, 13C and 15N nuclear magnetic resonance coordination shifts in Au(III), Pd(II) and Pt(II) chloride complexes with phenylpyridines

1H, 13C and 15N nuclear magnetic resonance studies of gold(III), palladium(II) and platinum(II) chloride complexes with phenylpyridines (PPY: 4-phenylpyridine, 4ppy; 3-phenylpyridine, 3ppy; and 2-phenylpyridine, 2ppy) having the general formulae [Au(PPY)Cl3], trans-/cis-[Pd(PPY)2Cl2] and trans-/cis-[Pt(PPY)2Cl2] were performed and the respective chemical shifts (delta1H, delta13C and delta15N) reported. 1H, 13C and 15N coordination shifts (i.e. differences between chemical shifts of the same atom in the complex and ligand molecules: Delta(coord)(1H) = delta(complex)(1H)-delta(ligand)(1H), Delta(coord)(13C) = delta(complex)(13C)-delta(ligand)(13C), Delta(coord)(15N) = delta(complex)(15N)-delta(ligand)(15N)) were discussed in relation to the type of the central atom (Au(III), Pd(II) and Pt(II)), geometry (trans-/cis-) and the position of a phenyl group in the pyridine ring system.

A briefing on aurophilicity

There is now compelling experimental evidence for the existence of specific intra- and intermolecular bonding between seemingly closed-shell gold(I) centers (5d10) which manifests itself in all areas of gold chemistry. This "aurophilic interaction", which had not been predicted by conventional valence theory, was found to be associated with binding energies in some cases exceeding even those of strong hydrogen bonds and therefore to be highly significant in co-determining molecular structure and dynamics. In high-level theoretical treatments the attraction is rationalized as a "super van der Waals bonding" based on particularly strong relativistic, dispersion and correlation effects (critical review, 265 references).