María Rodríguez-Castillo

Reactivity of gold nanoparticles towards N-heterocyclic carbenes

The reaction of gold nanoparticles with benzimididazol-2-ylidene ligands leads to the formation of well-defined bis-carbene gold(i) complexes, as shown by characterization techniques such as powder XRD and solid state NMR.

Golden Metallopolymers with an Active T1 State via Coordination of Poly(4-vinyl)pyridine to Pentahalophenyl-Gold(I) Precursors

Brightly phosphorescent gold-based metallopolymers have been synthesized by reaction of nonluminescent reactants comprised of the commercially available polymer PVP = poly(4-vinylpyridine) and the Au(I) precursors [Au(C(6)X(5))THT] (X = F or Cl; THT = tetrahydrothiophene). The metallopolymer products exhibit remarkable photoluminescence properties including high solid-state quantum yield (up to 0.63 at RT) and coarse- and fine-tuning to multiple phosphorescence bands across the visible spectrum via luminescence thermochromism and site-selective excitation. The emissions are caused by intrachain and interchain aurophilic interactions between the linear Au(I) complexes in the metallopolymers. This investigation provides further manifestations of interesting chemistry and photophysics in N-heterocyclic coordination compounds of Au(I) by expansion from the small-molecule to the metallopolymer regime. The spectroscopic and material properties of the new class of metallopolymers are desirable for future studies that will utilize them as emitters for photonic applications such as polymer light-emitting diodes and sensors.

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.

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.

Influence of the electronic characteristics of N-donor ligands in the excited state of heteronuclear gold(I)-copper(I) systems.

By reaction of the heterometallic gold-silver complexes [{AuAg(C(6)F(5))(2)(N≡C-Me)}(2)](n) or [{AuAg(C(6)Cl(5))(2)(N≡C-Me)}(2)](n) and CuCl in the presence of pyrimidine and different nitrile ligands (acetonitrile, benzonitrile, and cinnamonitrile), the heteronuclear complexes {[Au(C(6)X(5))(2)][Cu(L)(μ(2)-C(4)H(4)N(2))]}(n) (X = F and L = N≡C-Me (1), L = N≡C-Ph (2) or N≡C-CH═CH-Ph (3); X = Cl and L = N≡C-Me (4), N≡C-Ph (5), N≡C-CH═CH-Ph (6)) have been prepared. The crystal structures of complexes {[Au(C(6)X(5))(2)][Cu(L)(μ(2)-C(4)H(4)N(2))]}(n) (X = F; L = N≡C-CH═CH-Ph (3), X = Cl; L = N≡C-Ph (5)) have been determined by X-ray diffraction studies. The crystal structures of both complexes consists of polymeric chains formed by the repetition of [Au(C(6)X(5))(2)][Cu(L)(μ(2)-C(4)H(4)N(2))] units through copper-pyrimidine bonds. Complexes 1, 2, 4, and 5 are brightly luminescent in the solid state at room temperature and at 77 K with lifetimes in the microseconds range. These compounds are also luminescent in solution, displaying different photophysical behaviors depending on the donor characteristics of the solvents used. The distortion in the excited state allows an associative attack by donor solvents quenching one of the emitting excited states. DFT optimizations of the ground (S(0)) and lowest triplet excited state (T(1)) display the structure distortion of the complexes upon electronic excitation. The molecular orbitals involved in the electronic transitions responsible for the phosphorescence in the case of the complexes 1, 2, 4, and 5 are related to metal (gold-copper) to ligand (pyrimidine) charge transfer transitions, while in the case of the nonluminescent complexes 3 and 6, the nonradiative electronic transition arises from metal (gold-copper) to ligand (cinnamonitrile) charge transfer transitions.

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)(η1-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)(η3-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.

Experimental and Theoretical Study of the Reactivity of Gold Nanoparticles towards Benzimidazole-2-ylidene Ligands

The reactivity of benzimidazol-2-ylidenes with respect to gold nanoparticles (AuNPs) has been investigated using a combined experimental and computational approach. First, the grafting of benzimidazol-2-ylidenes bearing benzyl groups on the nitrogen atoms is described, and comparisons are made with structurally similar N-heterocyclic carbenes (NHCs) bearing other N-groups. Similar reactivity was observed for all NHCs, with 1) the erosion of the AuNPs under the effect of the NHC and 2) the formation of bis(NHC) gold complexes. DFT calculations were performed to investigate the modes of grafting of such ligands, to determine adsorption energies, and to rationalize the spectroscopic data. Two types of computational models were developed to describe the grafting onto large or small AuNPs, with either periodic or cluster-type DFT calculations. Calculations of NMR parameters were performed on some of these models, and discussed in light of the experimental data.

Nanocomposites based on Hofmann-type structure NiII(pz)[NiII(CN)4] (pz = pyrazine) nanoparticles for reversible iodine capture

Hybrid nanocomposites based on nanoparticles with the Hofmann-type structure NiII(pz)[NiII(CN)4] (where pz = pyrazine) confined into mesoporous silica or porous glass pearls were synthesised by sequential coordination of the molecular precursors into the pores of the functionalized matrices. Infrared (IR) and UV/Visible (UV-Vis) spectroscopy, powder X-ray diffraction (PXRD), and transmission electron microscopy (TEM) reveal the presence of uniformly-sized spherical NiII(pz)[NiII(CN)4] nanoparticles of 3–6 nm, which are homogeneously dispersed into the matrices. These nanocomposites are able to efficiently capture iodine from cyclohexane solutions with a maximum sorption capacity of 1.75 mmol per g of material. A particular emphasis is given on the mechanism of iodine sorption as well as on the sorption cycling ability of the materials.

Solvent Induced Luminescence in Supramolecular Heterobimetallic Gold(I)- Copper(I) Complexes with a Bidentate Nitrile Ligand

Heterobimetallic complexes (Cu(NC-Cy-CN)2)(Au(C6F5)2)·0.5 Toluene (1) and (Cu(NC-Cy- CN)2)(Au(C6F5)2)·CH2Cl2 (2) and (AuCu(C6F5)2(NC-Cy-CN)2)·CH2Cl2 (3) (with the same stoichiometry but different structure) have been synthesized and the crystal structure of complex 2·CH2Cl2 has been characterized through X-ray dif- fraction studies. The structure shows a cationic (Cu(NC-Cy-CN)2) + polymer that runs parallel to the crystallographic y axis, which is formed by the copper centers and the nitrile bridging ligands, and (Au(C6F5)2) - anions that link the polym- eric chain via non-classical C-H···Au hydrogen bonds. Complexes 1, 2 and 3 only differ in the solvents and the time used for their synthesis but this greatly affects their photophysical properties. Complexes 1, 2 and 3 are brightly luminescent in solid state at room temperature with lifetimes in the microseconds range. Complexes 1 and 2 display emissions arising from IL transitions while for complex 3 an emission arising from a MLCT is proposed.

Cooperative Au(I)···Au(I) Interactions and Hydrogen Bonding as Origin of a Luminescent Adeninate Hydrogel Formed by Ultrathin Molecular Nanowires

Two water-soluble [Au(9 N-adeninate)(PR3)] complexes (PR3 = PMe3 (1); PTA (3)) were synthesized by the coordination of the respective cationic [Au(PR3)]+ fragment to the 9 N position of the adeninate anion. Both complexes crystallize as dimers by aurophilic contacts of 3.2081(6) Å in 1 and 3.0942(7) and 3.0969(7) Å in 3, but different packings are observed due to the crystallizing solvent choice and the nature of the ancillary phosphine ligand. At this regard, different supramolecular behavior is observed in water, ranges from the formation of ultrathin nanowires of 5.3 ± 1.9 nm of diameter and up to 1.5 μm in length and leads to a blue-luminescent hydrogel for 1, to the single-crystallization of 3. Parallel computational studies carried out show that aurophilicity and N-H···N or O-H···N hydrogen bonding are comparable in strength, suggesting a competition between all types of weak forces in the final observed macroscopic properties.