Tania Lasanta

Combining Aurophilic Interactions and Halogen Bonding To Control the Luminescence from Bimetallic Gold−Silver Clusters

The luminescence in a series of new bimetallic gold-silver vapochromic structures can be efficiently switched among different colors simply by exposure to solvent vapors. The emission color in these systems is controlled by both aurophilic interactions and halogen bonding, which affect the emission energy through different orbitals.

Making the golden connection: reversible mechanochemical and vapochemical switching of luminescence from bimetallic gold-silver clusters associated through aurophilic interactions.

Aiming at the development of new architectures within the context of the quest for strongly luminescent materials with tunable emission, we utilized the propensity of the robust bimetallic clusters [Au₂Ag₂(R(I)/R(II))₄] (R(I) = 4-C₆F₄I, R(II) = 2-C₆F₄I) for self-assembly through aurophilic interactions. With a de novo approach that combines the coordination and halogen-bonding potential of aromatic heteroperhalogenated ligands, we have generated a family of remarkably luminescent bimetallic materials that provide grounds to address the relevance, relative effects, and synergistic action of the two interactions in the underlying photophysics. By polymerizing the green-emitting (λ(max)(em) = 540 nm) monomer [Au₂Ag₂R(II)₄(tfa)₂]²⁻ (tfa = trifluoroacetate) to a red-emitting (λ(max)(em) = 660 nm) polymer [Au₂Ag₂R(II)₄(MeCN)₂](n), we demonstrate herein that the degree of cluster association in these materials can be effectively and reversibly switched simply by applying mechanochemical and/or vapochemical stimuli in the solid state as well as by solvatochemistry in solution, the reactions being coincident with a dramatic switching of the intense, readily perceptible photoluminescence. We demonstrate that the key event in the related equilibrium is the evolution of a metastable yellow emitter (λ(max)(em) = 580 nm) for which the structure determination in the case of the ligand R(II) revealed a dimeric nonsolvated topology [Au₂Ag₂R(II)₄]₂. Taken together, these results reveal a two-stage scenario for the aurophilic-driven self-assembly of the bimetallic clusters [Au₂Ag₂(R(I)/R(II))₄]: (1) initial association of the green-emitting monomers to form metastable yellow-emitting dimers and desolvation followed by (2) resolvation of the dimers and their self-assembly to form a red-emitting linear architecture with delocalized frontier orbitals and a reduced energy gap. The green emission from [Au₂Ag₂R(II)₄(tfa)₂]²⁻ (λ(max)(em) = 540 nm) exceeds the highest energy observed for [Au₂Ag₂]-based structures to date, thereby expanding the spectral slice for emission from related structures beyond 140 nm, from the green region to the deep-red region.

Amalgamating at the molecular level. A study of the strong closed-shell Au(I)···Hg(II) interaction.

Complex {[Hg(C(6)F(5))(2)][Au(C(6)F(5))(PMe(3))](2)}(n)2 displays unsupported Au(I)···Hg(II) and Au(I)···Au(I) interactions. Its crystal structure displays a polymeric -(Au-Hg-Au-Au-Hg-Au)(n)- disposition. Ab initio calculations show very strong Au(I)···Hg(II) and Au(I)···Au(I) closed-shell interactions of -73.3 kJ mol(-1) and -57.0 kJ mol(-1), respectively, which have a dispersive (van der Waals) nature and are strengthened by large relativistic effects (>20%).

Experimental and theoretical evidence of the existence of gold(I)···mercury(II) interactions in solution through fluorescence-quenching measurements.

Heteronuclear complexes {[Hg(R)2][Au(R)(PMe3)]2}n (R=R=C6Cl2F3 (3); R=R=C6F5 (4); R=C6Cl2F3, R=C6F5 (5); R=C6F5, R=C6Cl2F3 (6)) were prepared by the treatment of the corresponding organomercury compounds, [Hg(C6X5)2], with two equivalents of [Au(C6X5)(PMe3)]. Their crystal structures, as determined by using X-ray diffraction methods, display Au···Hg interactions. Although only compound 4 and 5 show luminescence in the solid state, all of these compounds quench the fluorescence of naphthalene in solution. Solution studies of these derivatives suggest a cooperative effect of the gold(I) center in switching on the quenching capabilities of the [Hg(C6X5)2] synthon with naphthalene. Theoretical studies confirmed the quenching ability of the organomercury species in the presence of gold.

Heterometallic gold(I)–thallium(I) compounds with crown thioethers

The polymeric Au/Tl compounds [{Au(C6X5)2}Tl]n (X = Cl, F) react with the crown thioethers 1,4,7-trithiacyclononane ([9]aneS3), 1,5,8,11-tetrathiacyclotetradecane ([14]aneS4), and 1,4,7,10,13,16,19,22-octathiacyclotetracosane ([24]aneS8) in an appropriate molar ratio to afford [{Au(C6X5)2}Tl(L)]2 [L = [9]aneS3, X = Cl (1), F (4); L = [14]aneS4, X = Cl (2), F (5)], [{Au(C6Cl5)2}2Tl2([24]aneS8)]n (3) or [{Au(C6F5)2}2Tl2([24]aneS8)] (6). X-ray diffraction studies of 3, 4 and 6 reveal polymeric (3) or tetranuclear (4, 6) structures formed via Tl-S bonds and AuTl or AuTl and AuAu contacts. All the complexes are luminescent in the solid state, but not in solution, where the metal-metal interactions, which are responsible for the luminescence, are no longer present. DFT calculations on representative model systems of complexes 3, 4 and 6 have also been carried out in order to determine the origin of the electronic transitions responsible for their optical properties.