M. Elena Olmos

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.

Vapochromic behavior of {Ag2(Et2O)2[Au(C6F5)2]2}n with volatile organic compounds.

The vapochromic behaviors of {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1), Me2CO (2), THF (3), CH3CN (4)) were studied. {Ag2L2[Au(C6F5)2]2}n (L = Et2O (1)) was synthesized by the reaction of [Bu4N][Au(C6F5)2] with AgOClO3 in 1:1 molar ratio in CH2Cl2/Et2O (1:2). 1 was used as starting material with THF to form {Ag2L2[Au(C6F5)2]2}n (L = THF (3)). 3 crystallizes in the monoclinic space group C2/c and consists of tetranuclear units linked together via aurophilic contacts resulting in the formation of a 1D polymer that runs parallel to the crystallographic z axis. The gold(I) atoms are linearly coordinated to two pentafluorophenyl groups and display additional Au...Ag close contacts within the tetranuclear units with distances of 2.7582(3) and 2.7709(3) A. Each silver(I) center is bonded to the two oxygen atoms of the THF molecules with a Ag-O bond distance of 2.307(3) A. TGA analysis showed that 1 loses two molecules of the coordinated solvent per molecular unit (1st one: 75-100 degrees, second one: 150-175 degrees C), whereas 2, 3, and 4 lose both volatile organic compounds (VOCs) and fluorinated ligands in a less well defined manner. Each complex loses both the fluorinated ligands and the VOCs by a temperature of about 325 degrees C to give a 1:1 gold/silver product. X-ray powder diffraction studies confirm that the reaction of vapors of VOCs with 1 in the solid state produce complete substitution of the ether molecules by the new VOC. The VOCs are replaced in the order CH3CN > Me2CO > THF > Et2O, with the ether being the easiest to replace. {Ag2(Et2O)2[Au(C6F5)2]2}n and {Ag2(THF)2[Au(C6F5)2]2} n both luminesce at room temperature and at 77 K in the solid state. Emission maxima are independent of the excitation wavelength used below about 500 nm. Emission maxima are obtained at 585 nm (ether) and 544 nm (THF) at room temperature and at 605 nm (ether) and 567 nm (THF) at 77 K.

Experimental and theoretical evidence of the first Au(I)⋯Bi(III) interaction

Complex [Au(C6F5)2][Bi(C6H4CH2NMe(2)-2)2] displays the first example of an interaction between Au(I) and Bi(III), the nature of which is shown to be consistent with the presence of a high ionic contribution (79%) and a dispersion type (van der Waals) interaction (21%).

Unsupported Au(I)⋯Cu(I) interactions: influence of nitrile ligands and aurophilicity on the structure and luminescence

The synthesis, structural characterization and the study of the photophysical properties of complexes [AuCu(C6F5)2(N[triple bond]C-CH3)2] 1, [AuCu(C6F5)2(N[triple bond]C-Ph)2]2 2, and [AuCu(C6F5)2(N[triple bond]C-CH=CH-Ph)2] 3 have been carried out. The crystal structures of complexes 1-3 consist of dinuclear Au-Cu units built from mediated metallophilic Au(I)...Cu(I) interactions. In the case of complex 2 two dinuclear units interact via an aurophilic interaction leading to a tetranuclear Cu-Au-Au-Cu arrangement. Complex 2 is brightly luminescent in solid state at room temperature and at 77 K with a lifetime in the nanoseconds range, while complexes 1 and 3 do not display luminescence under the same conditions. The presence of the aurophilic interaction in complex 2 seems to be responsible for the blue luminescence observed. DFT and time-dependent DFT calculations agree with the experimental results and support the idea that the origin of the luminescence of these complexes arise from orbitals located in the interacting metals.

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%).

Multiple Evidence for Gold(I)⋅⋅⋅Silver(I) Interactions in Solution

[AuAg3(C6F5)(CF3CO2)3(CH2PPh3)]n (2) was prepared by reaction of [Au(C6F5)(CH2PPh3)] (1) and [Ag(CF3CO2)] (1:3). The crystal structures of complexes 1 and 2 were determined by X-ray diffraction, and the latter shows a polymeric 2D arrangement built by Au...Ag, Ag...Ag, and Ag...O contacts. The metallophilic interactions observed in 2 in the solid state seem to be preserved in concentrated THF solutions, as suggested by EXAFS, pulsed-gradient spin-echo NMR, and photophysical studies, which showed that the structural motif [AuAg3(C6F5)(CF3CO2)3(CH2PPh3)] is maintained under such conditions. Time-dependent DFT calculations agree with the experimental photophysical energies and suggest a metal-to-ligand charge-transfer phosphorescence process. Ab initio calculations give an estimated interaction energy of around 60 kJ mol(-1) for each Au...Ag interaction.

Recent Developments in Arylgold(I) Chemistry

Publisher Summary This chapter focuses on recent developments in monovalent arylgold derivatives. While traditionally mononuclear complexes are the most plentiful arylgold(I) derivatives, the growing interest in the study and understanding of closed-shell metal–metal interactions have led to the synthesis of numerous examples of homo- or hetero-atomic associations in which the presence of intra- or inter-molecular metal–metal interactions may play an important role and lead to interesting optical properties. This chapter presents the different synthetic routes to arylgold(I) derivatives and discusses their crystal structures in an increasing order of nuclearity from mononuclear species to polynuclear complexes and according to the neutral or ionic nature of the arylgold species. The discussion of the mononuclear complexes includes: neutral, anionic and cationic; while that of dinuclear complexes includes: homonuclear complexes and heteronuclear complexes; of trinuclear complexes includes: homonuclear complexes and heteronuclear complexes; of tetranuclear complexes includes: homonuclear and heteronuclear; and that of higher nuclearity complexes includes: penta-, hexa- and heptanuclear complexes and polynuclear complexes of arylgold(I) chemistry.

[{AuTl(C6Cl5)2(toluene)}2(dioxane)]: A striking structure that leads to a blue luminescence

The complex [{AuTl(C6Cl5)2(toluene)}2(dioxane)] displays a structure with the thallium(I) center in an unprecedented trigonal planar environment, showing the shortest Au–Tl interaction ever found, a toluene molecule in a η6-mode and the “disappearance” of the Tl(I) inert pair, usually stereochemically active. These characteristics are responsible for its unusual luminescent behaviour.

Pyridine gold complexes. an emerging class of luminescent materials

Pyridine-type ligands are considered one of the most versatile ligands in photochemistry since they can act as emitters themselves or as donor or acceptors of electronic density depending on the electronic character of the substituents of the rings and the metal centers bonded to them. Gold is a well known metal with an impressive tendency to form metal aggregates through metal-metal interactions and, therefore, gold complexes bearing these ligands are tailored derivatives with potential as emitting materials. The new possibilities of experimental and theoretical studies that appear with the easy synthesis of a new class of luminescent materials formed by the combination of pyridine ligands and gold are shown here.