Remarkable Aurophilicity and Photoluminescence Thermochromism in a Homoleptic Cyclic Trinuclear Gold(I) Imidazolate Complex

A new aurophilically-bonded cyclic trinuclear gold­(I) complex, tris­[μ₂-(1-ethylimidazolato-N³,C²)­gold­(I)] ([Au₃(EtIm)₃], <b>1</b>), has been synthesized and characterized by temperature-dependent crystallographic and photophysical investigations. The crystal packing of <b>1</b> reveals two independent molecules in the unit cell, signifying two distinct pairs of dimer-of-trimer units convened by pairwise intermolecular Au···Au interactions of 3.0662(3) and 3.1407(3) Å at 100 K, representing the shortest pairwise intermolecular aurophilic interactions among all cyclic trimetallic gold­(I) complexes to date. Remarkably, crystals of <b>1</b> exhibit gigantic photoluminescence thermochromism of 10164 cm^–1from violet to red!attributed to internal conversion between a higher-energy (T₂ → S₀; λ_max ∼409 nm) and lower-energy (T₁ → S₀; λ_max ∼700 nm) phosphorescent band below and above 200 K, respectively, likely representing an excited-state phase change

New Coordination Polymers of Copper(I) and Silver(I) with Pyrazine and Piperazine: A Step Toward “Green” Chemistry and Optoelectronic Applications

Five coordination polymers and one hexanuclear cluster have been obtained, and their crystal structures were determined upon reaction of Cu­(I) or Ag­(I) precursors with pyrazine (Pyz) or piperazine (Ppz). Five complexes are mixed-imine-ligand with anionic-fluorinated pyrazolate [3,5-(CF₃)₂Pz]⁻ ([Pz^F]⁻) besides Pyz or Ppz, whereas the sixth had the neutral diimine as a single chromophore. Complexes <b>1</b>–<b>3</b> are isomers of the same Cu/Pz^F/Pyz composition with the same or different unit cell stoichiometry, namely, {Cu₆[3,5-(CF₃)₂Pz]₆­(Pyz)₃­(CH₂Cl₂)}_∞ (<b>1</b>·CH₂Cl₂), {Cu₂[3,5-(CF₃)₂Pz]}₂­(Pyz)₂­·toluene}_∞ (<b>2</b>·toluene), and {Cu₃[3,5-(CF₃)₂Pz]₃­(Pyz)_1.5­·1.5benzene}_∞ (<b>3</b>·1.5benzene), respectively. Altering only the metal attains {Ag₆[3,5-(CF₃)₂Pz]₆­(Pyz)₂­·2benzene} (<b>4</b>·2benzene), while also changing the neutral diimine attains {Ag₂[3,5-(CF₃)₂Pz]₂­(Ppz)}_∞ (<b>5</b>). Using Pyz without an anionic imine yields {[Cu­(Pyz)­(MeCN)₂]­[BF₄]}_∞ (<b>6</b>). The crystal structure of <b>1</b> shows two trimers linked together with two pyrazine ligands. Crystals of <b>2</b> represent a metal–organic framework (MOF-TW1) with significant surface area (1278 m²/g) and porosity (23.7% void volume) without considering toluene adsorbates in channels. MOF-TW1 was obtained serendipitously upon a reaction attempt to attain a mixed-metal product, instead attaining a Cu­(I)-only product with interconnected four-coordinate dinuclear units. Likewise, <b>3</b> was obtained through a transmetalation of all Ag atoms in <b>4</b> to replace them by Cu atoms. Three reactions (to obtain <b>1</b>, <b>4</b>, and <b>5</b>) were successfully carried out by both solvent-mediated and solventless transformations, whereas <b>2</b> and <b>3</b> were obtained only by solvent-mediated reactions, while <b>6</b> was attainable only by solventless transformations. The solventless transformations occurred either by sublimation and vapor diffusion or by mechanical grinding at ambient laboratory conditionswithout the aid of heating, high pressure, vacuum, or any automated equipment. All transformations could be monitored by the human eye as the reaction progresses, as evidenced by progressive discoloration and/or luminescence changes. All crystal structures were obtained with the aid of conventional crystal growth methods from organic solvents for bulk products obtained from both solvelntless and solvent-mediated reactions. Powder X-ray diffraction was used to compare bulk products with one another and the crystallographic products. All Cu­(I) products are colored and nonluminescent; the progress of their vapor diffusion-based solventless reactions can be followed by gradual discoloration of white solid reactants and/or quenching precursor’s phosphorescence. Both Ag­(I) products were colorless with <b>4</b> being luminescent but not <b>5</b>

Diosmium carbonyl sawhorse complexes containing a ferrocenedicarboxylato ligand

In an attempt to prepare a supramolecular assembly consisting of two, three, or four diosmium carbonyl sawhorse units linked together by dicarboxylato ligands, the reaction of [Os3(CO)12] with ferrocene-1,1′-dicarboxylic acid, Fe(C5H4COOH)2, was carried out with microwave heating. Instead of an assembly, the lone diosmium product was the single sawhorse complex [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)6] (1) with a tetradentate doubly bridging Fe(C5H4CO2–)2 ligand, a metal–metal single bond, four equatorial carbonyl ligands, and two axial carbonyl ligands. Two additional sawhorse complexes, [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)4(tri-p-tolylphosphine)2] (2) and [Os2(μ-ferrocene-1,1′-dicarboxylato)(CO)4(N,N-dimethylaminomethylferrocene)2] (3), were prepared by substituting the axial CO ligands in 1 with P- or N-donor ligands, respectively. Clusters 1, 2, and 3 represent the first examples of carbonyl sawhorse complexes with ferrocenedicarboxylato ligands, and all three were characterized with single-crystal X-ray diffraction studies. </p

Fluorinated Antimony(V) Tetraarylporphyrins as High-Valent Electron Acceptors with Unparalleled Reduction Potentials

A series of fluorinated antimony(V) porphyrins, SbTPP(OMe)2·PF6, SbTPP(OTFE)2·PF6, SbT(4F)PP(OMe)2·PF6, SbT(35F)PP(OMe)2·PF6, SbT(345F)PP(OMe)2·PF6, SbT(4CF3)PP(OMe)2·PF6, SbT(35CF3)PP(OMe)2·PF6, and SbT(35CF3)PP(OTFE)2·PF6, have been synthesized with phenyl [P], 4-fluorophenyl [(4F)P], 3,5-difluorophenyl [(35F)P], 3,4,5-difluorophenyl [(345F)P], 4-trifluoromethylphenyl [(4CF3)P], and 3,5-bis(trifluoromethyl)phenyl [(35CF3)P], in the meso-positions. Additionally, the SbTPP(OTFE)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6 carry trifluoroethoxy units in their axial-positions. The fluorination on the porphyrin peripherals ranges from zero fluorine atoms in SbTPP(OMe)2·PF6 to 30 fluorine atoms in SbT(35CF3)PP(OTFE)2·PF6. X-ray crystallography confirmed the structures of the investigated antimony(V) porphyrins. The absorption spectra depend on the number of fluorine atoms as it is blue-shifted with increasing fluorination. The series also exhibited rich redox chemistry with two reduction processes and one oxidation process. Remarkably, these porphyrins manifested the lowest reduction potentials reported among the main-group porphyrins, which are as low as −0.08 V vs SCE for SbT(35CF3)PP(OTFE)2·PF6. On the contrary, the oxidation potentials were found to be very large, that is equal to 2.20 V vs SCE or even higher for SbT(4CF3)PP(OMe)2·PF6 or SbT(35CF3)PP(OMe)2·PF6 and SbT(35CF3)PP(OTFE)2·PF6, respectively. These unprecedented potentials are due to a combination of two factors: (i) the +5-oxidation state of antimony in the porphyrin cavity and (ii) the presence of the strong electron-withdrawing fluorine atoms on the porphyrin peripherals. Density functional theory (DFT) calculations were used to support the experimental results. The systematic study of antimony(V) porphyrins, especially their high potentials, make them ideal for the construction of photoelectrodes and excellent electron acceptors for photoelectrochemical cells and artificial photosynthetic systems, respectively, for solar energy conversion and storage applications

Optoelectronic Tuning of Organoborylazadipyrromethenes via Effective Electronegativity at the Metalloid Center

Organoborylazadipyrromethenes were synthesized from free base and fluoroborylazadipyrromethenes and characterized with regard to their structural and electronic properties. B–N bond lengths, along with photophysical and redox behavior, appear dependent on the effective electronegativity at the boron atom as tuned by its substituents, with stronger electronegativity correlating to a shorter B–N bond length, red-shifted absorbance, enhanced fluorescence lifetime and yield, and positively shifted redox potentials

Simultaneous Chronoamperometry and Piezoelectric Microgravimetry Determination of Nitroaromatic Explosives Using Molecularly Imprinted Thiophene Polymers

Thin films of conducting molecularly imprinted polymers (MIPs) were prepared for simultaneous chronoamperometry (CA) and piezoelectric microgravimetry (PM) determination of several explosive nitroaromatic compounds (NTs) including 2,4,6-trinitrophenol (TNP), 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrobenzene (TNB), and 2,4-dinitrotoluene (DNT). For that, the bis­(2,2′-bithienyl)-(4-aminophenyl)­methane <b>1</b> functional monomer allowing for π–π stacking recognition of the NTs was designed and synthesized. Both theoretical DFT calculations at the M062X/3-21G* level and experimental fluorescence titrations indicated the 1:1 stoichiometry of the <b>1</b> and NT prepolymerization complexes formed in solutions. The NT-templated MIP (MIP-NT) films were deposited by potentiodynamic electropolymerization on the Au-coated quartz crystal resonators (Au-QCRs) from solutions of <b>1</b> and each of the NT templates at the <b>1</b>-to-NT mole ratio of 1:1. For sensing application, the NTs were extracted from the MIP-NT films. Completeness of the extraction was confirmed by the presence and absence before and after extraction, respectively, of both the XPS peak of the N 1s electrons of the NT nitro groups and the DPV peak of electroreduction of the NTs for the MIP-NT. Ultimately, the recognition signal was transduced to the analytical signal of simultaneous changes of CA cathodic current and PM resonant frequency. The limit of detection (LOD) for NTs was in the range of hundreds and tens micromolar for CA and PM, respectively. Moreover, selectivity with respect to common interferences of the chemosensors was in the range 2.1–4.8, as determined by molecular cross-imprinting

Three Component Cascade Reaction of Cyclohexanones, Aryl Amines, and Benzoylmethylene Malonates: Cooperative Enamine-Brønsted Acid Approach to Tetrahydroindoles

A three-component cascade reaction comprising cyclic ketones, arylamines, and benzoylmethylene malonates has been developed to access 4,5,6,7-tetrahydro-1H-indoles. The reaction was achieved through cooperative enamine-Brønsted catalysis in high yields with wide substrate scopes. Mechanistic studies identified the role of the Brønsted acid catalyst and revealed the formation of an imine intermediate, which was confirmed by X-ray crystallography

Three Component Cascade Reaction of Cyclohexanones, Aryl Amines, and Benzoylmethylene Malonates: Cooperative Enamine-Brønsted Acid Approach to Tetrahydroindoles

A three-component cascade reaction comprising cyclic ketones, arylamines, and benzoylmethylene malonates has been developed to access 4,5,6,7-tetrahydro-1H-indoles. The reaction was achieved through cooperative enamine-Brønsted catalysis in high yields with wide substrate scopes. Mechanistic studies identified the role of the Brønsted acid catalyst and revealed the formation of an imine intermediate, which was confirmed by X-ray crystallography

Three Component Cascade Reaction of Cyclohexanones, Aryl Amines, and Benzoylmethylene Malonates: Cooperative Enamine-Brønsted Acid Approach to Tetrahydroindoles

A three-component cascade reaction comprising cyclic ketones, arylamines, and benzoylmethylene malonates has been developed to access 4,5,6,7-tetrahydro-1H-indoles. The reaction was achieved through cooperative enamine-Brønsted catalysis in high yields with wide substrate scopes. Mechanistic studies identified the role of the Brønsted acid catalyst and revealed the formation of an imine intermediate, which was confirmed by X-ray crystallography

Assessing the Potential of Peropyrene as a Singlet Fission Material: Photophysical Properties in Solution and the Solid State

The photophysical behavior of the polycyclic aromatic hydrocarbon peropyrene is studied both in dilute solution and in the solid state, with the goal of evaluating this molecule as a singlet fission (SF) material. In solution, the fluorescence quantum yield is consistently in the range 0.90–0.95, while the fluorescence lifetime changes from 3.2 to 5.5 ns. Analysis of the solvent dependence of the radiative rate provides evidence that the bright ¹B_u singlet state mixes with a second, optically dark state. The presence of a dark state slightly above the ¹B_u state in energy is confirmed using two-photon fluorescence excitation spectroscopy. The crystal structure of solid peropyrene consists of a herringbone arrangement of π-stacked molecular pairs, similar to the α-polymorph of perylene. There are two emitting species, centered at approximately 550 and 650 nm, both of which are formed within the 15 ps time resolution of the experiment, and which relax independently via biexponential decays. We find no evidence for rapid SF in the peropyrene crystals, most likely due to the large shift of the singlet state to lower energy where it no longer fulfills the energy condition for SF. These results demonstrate how both energetics and crystal packing influence the ability of a molecule to function as a SF material