Computational Chemistry Meets Experiments for Explaining the Behavior of Bibenzyl: A Thermochemical and Spectroscopic (Infrared, Raman, and NMR) Investigation

The structure, conformational behavior, and spectroscopic parameters of bibenzyl have been investigated by a computational protocol including proper treatment of anharmonic and hindered rotor contributions. Conventional hybrid functionals overstabilize the <i>anti</i> conformer while low-order post-Hartree–Fock (MP2) approaches strongly favor the <i>gauche</i> conformer. However, inclusion of semiempirical dispersion effects in density functionals or coupled cluster post-Hartree–Fock models agree in forecasting the simultaneous presence of both conformers in the gas phase with a slightly larger stability (0.7 kcal·mol^–1) of the <i>gauche</i> conformer. Addition of thermal and entropic effects finally leads to very close Gibbs free energies for both conformers and, thus, to a slight preference for the gauche form due to statistical factors (2 vs 1). The situation remains essentially the same in solution. On these grounds, perturbative vibrational computations including both electrical and mechanical anharmonicities lead to IR and Raman spectra in remarkable agreement with experiment. Full assignment of the IR spectra explains the presence of peaks from gauche or anti conformers. Comparison between computed and experimental Raman spectra confirms that both conformers are present in liquid phase, whereas the anti conformer seems to be preponderant in the solid state. Also computed NMR parameters are in good agreement with experiment

New Insights To Simulate the Luminescence Properties of Pt(II) Complexes Using Quantum Calculations

The present manuscript reports a thorough quantum investigation on the luminescence properties of three monoplatinum­(II) complexes. First, the simulated bond lengths at the ground state are compared to the observed ones, and the simulated electronic transitions are compared to the reported ones in the literature in order to assess our methodology. In a second time we show that geometries from the first triplet excited state are similar to the ground state ones. Simulations of the phosphorescence spectra from the first triplet excited states have been performed taking into account the vibronic coupling effects together with mode-mixing (Dushinsky) and solvent effects. Our simulations are compared with the observed ones already reported in the literature and are in good agreement. The calculations demonstrate that the normal modes of low energy are of great importance on the phosphorescence signature. When temperature effects are taken into account, the simulated phosphorescence spectra are drastically improved. An analysis of the computational time shows that the vibronic coupling simulation is cost-effective and thus can be extended to treat large transition metal complexes. In addition to the intrinsic importance of the investigated targets, this work provides a robust method to simulate phosphorescence spectra and to increase the duality experiment-theory

TD-DFT Benchmark on Inorganic Pt(II) and Ir(III) Complexes

We report in the present paper a comprehensive investigation of representative Pt­(II) and Ir­(III) complexes with special reference to their one-photon absorption spectra employing methods rooted in density functional theory and its time dependent extension. We have compared nine different functionals ranging from generalized gradient approximation (GGA) to global or range-separated hybrids, and two different basis sets, including pseudopotentials for 4 iridium and 7 platinum complexes. It turns out that hybrid functionals with the same exchange part give comparable results irrespective of the specific correlation functional (i.e., B3LYP is very close to B3PW91 and PBE0 is very close to MPW1PW91). More recent functionals, such as CAM-B3LYP and M06-2X, overestimate excitation energies, whereas local functionals (BP86 -GGA-, M06-L -Meta GGA-) strongly underestimate transition energies with respect to experimental results. As expected, basis set effects are weak, and the use of a triple-ζ polarized (def2-TZVP) basis set does not significantly improve the computed excitation energies with respect to a classical double-ζ basis set (LANL2DZ) augmented by polarization functions, but it significantly raises the computational effort

Structural and Spectroscopic Investigations of Two [Cu₄X₆]^2– (X = Cl^–, Br^–) Clusters: A Joint Theoretical and Experimental Work

Herein we report a joint experimental and theoretical investigation on two tetranuclear Cu­(I) clusters stabilized by halide ligands. These clusters are of high interest due to their spectroscopic and optical properties, more precisely both clusters exhibit thermochromism. The compounds synthesized by the hydrothermal method have been characterized by single-crystal X-ray diffraction, UV–visible spectroscopy and quantum calculations. Modeled structures have been investigated by means of DFT and TD-DFT methods. Anharmonic computations have been performed to better achieve the vibrational investigation. Computations of the triplet excited states permit us to get more insights into the structure and electronic structure of the excited states responsible for the luminescence properties. Calculations are in agreement with the observed phosphorescence wavelengths

Luminescence Properties of Al₂O₃:Ti in the Blue and Red Regions: A Combined Theoretical and Experimental Study

Using jointly experimental results and first-principles calculations, we unambiguously assign the underlying mechanisms behind two commonly observed luminescence bands for the Al2O3 material. Indeed, we show that the red band is associated with a Ti3+ d–d transition as expected, while the blue band is the combination of the Ti3+ + O– → Ti4+ + O2– and VO•+e– → VO× de-excitation processes. Thanks to our recent developments, which take into account the vibrational contributions to the electronic transitions in solids, we were able to simulate the luminescence spectra for the different signatures. The excellent agreement with the experiment demonstrates that it should be possible to predict the color of the material with a CIE chromaticity diagram. We also anticipated the luminescence signature of Al2O3:Ti,Ca and Al2O3:Ti,Be that were confirmed by experiment

Synthesis and Photoluminescence Properties of Ca₂Ga₂SiO₇:Eu³⁺ Red Phosphors with an Intense ⁵D₀ → ⁷F₄ Transition

Novel melilite-type Ca₂Ga₂SiO₇:Eu³⁺ red-emitting phosphors with different Eu³⁺ contents were synthesized via high-temperature solid-state reaction. The crystal structure, optical absorption, and photoluminescence properties were investigated, while density functional theory calculations were performed on the host lattice. The excitation spectra indicate that phosphors can be effectively excited by near-UV light for a potential application in white-light-emitting diodes. Because of the abnormally high intensity emission at about 700 nm arising from the ⁵D₀ → ⁷F₄ transition of Eu³⁺, the phosphors Ca₂Ga₂SiO₇:Eu³⁺ show a deep-red emission with chromaticity coordinates (0.639, 0.358)

Switching of Reverse Charge Transfers for a Rational Design of an OFF–ON Phosphorescent Chemodosimeter of Cyanide Anions

A rational approach to luminescence turn-on sensing of cyanide by a dicyanovinyl-substituted acetylide Pt­(II) complex, which primarily relies on the nucleophilic addition reaction of cyanide anions to the α-position of the dicyanovinyl group, is described. The strategy used for the design of this cyanide-selective sensor takes advantage of a switch of charge transfer from ML′CT to MLCT/L′LCT in this acetylide Pt­(II) sensor. As a result, this chromophore that exhibits almost no basal luminescence displays observable changes in its UV–visible spectrum and acquires strong phosphorescence upon addition of cyanide anions. DFT computations reveal that the frontier molecular orbitals of the anionic system obtained after addition of CN^– are drastically different from those of the neutral initial species. TD-DFT computations permitted a full assignment of the observed absorption bands and explained well the emissive properties of the species under consideration

A Twelve-Coordinated Iodide in a Cuboctahedral Silver(I) Skeleton

Three new halide-centered octanuclear silver­(I) complexes, [Ag₈(X)­{S₂P­(CH₂CH₂Ph)₂}₆]­(PF₆), X = F^–, <b>1</b>; Cl^–, <b>2</b>; Br^–, <b>3</b>; were prepared in the presence of the corresponding halide anions with silver­(I) salts and dithiophosphinate ligands. Structure analyses displayed that a Ag₈ cubic core can be modulated by the size effect of the central halide; however, an iodide-centered Ag₈ cluster was not found under similar reaction conditions. Interestingly, a luminescent dodecanuclear silver­(I) cluster, [Ag₁₂(μ₁₂-I)­(μ₃-I)₄{S₂P­(CH₂CH₂Ph)₂}₆]­(I), <b>4</b>; was then synthesized. The structure of <b>4</b> contains a novel μ₁₂-I at the center of a cuboctahedral silver­(I) atom cage, which is further stabilized by four additional μ₃-I and six dithiophosphinate ligands. To the best of our knowledge, the μ₁₂-I revealed in <b>4</b> is the highest coordination number for a halide ion authenticated by both experimental and computational studies. Previously, the μ₁₂-I was only observed in [PyH]­[{TpMo­(μ₃-S)₄Cu₃}₄(μ₁₂-I)]. The synthetic details, spectroscopic studies including multinuclear NMR and ESI-MS, structure elucidations by single crystal X-ray diffraction, and photoluminescence of <b>4</b> are reported herein

[Ag₇(H){E₂P(OR)₂}₆] (E = Se, S): Precursors for the Fabrication of Silver Nanoparticles

Reactions of Ag­(I) salt, NH₄(E₂P­(OR)₂) (R = ⁱPr, Et; E = Se, S), and NaBH₄ in a 7:6:1 ratio in CH₂Cl₂ at room temperature, led to the formation of hydride-centered heptanuclear silver clusters, [Ag₇(H)­{E₂P­(OR)₂}₆] (R = ⁱPr, E = Se (<b>3</b>): R = Et; E = S­(<b>4</b>). The reaction of [Ag₁₀(E)­{E₂P­(OR)₂}₈] with NaBH₄ in CH₂Cl₂ produced [Ag₈(H)­{E₂P­(OR)₂}₆]­(PF₆) (R = ⁱPr, E = Se (<b>1</b>): R = Et; E = S­(<b>2</b>)), which can be converted to clusters <b>3</b> and <b>4</b>, respectively, via the addition of 1 equiv of borohydride. Intriguingly clusters <b>1</b> and <b>2</b> can be regenerated via adding 1 equiv of Ag­(CH₃CN)₄PF₆ to the solution of compounds <b>3</b> and <b>4</b>, respectively. All complexes have been fully characterized by NMR (¹H, ⁷⁷Se, ¹⁰⁹Ag) spectroscopy, UV–vis, electrospray ionization mass spectrometry (ESI-MS), FT-IR, thermogravimetric analysis (TGA), and elemental analysis, and molecular structures of <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> were clearly established by single crystal X-ray diffraction. Both <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> exhibit a tricapped tetrahedral Ag₇ skeleton, which is inscribed within an E₁₂ icosahedron constituted by six dialkyl dichalcogenophosphate ligands in a tetrametallic-tetraconnective (μ₂, μ₂) bonding mode. Density functional theory (DFT) calculations on the models [Ag₇(H)­(E₂PH₂)₆] (E = Se: <b>3′</b>; E = S: <b>4′</b>) yielded to a tricapped, slightly elongated tetrahedral silver skeleton, and time-dependent DFT (TDDFT) calculations reproduce satisfyingly the UV–vis spectrum with computed transitions at 452 and 423 nm for <b>3′</b> and 378 nm for <b>4′</b>. Intriguingly further reactions of [Ag₇(H)­{E₂P­(OR)₂}₆] with 8-fold excess amounts of NaBH₄ produced monodisperse silver nanoparticles with an averaged particle size of 30 nm, which are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and UV–vis absorption spectrum

C–H Activation of 2,4,6-Triphenylphosphinine: Synthesis and Characterization of the First Homoleptic Phosphinine–Iridium(III) Complex <i>fac</i>-[Ir(C^P)₃]

Access to homoleptic phosphinine-based coordination compounds of d⁶ metals has so far remained elusive. We report here on the preparation and full characterization of the first homoleptic phosphinine–iridium­(III) complex, obtained by C–H activation of 2,4,6-triphenylphosphinine with [Ir­(acac)₃]. This result opens up new perspectives for the implementation of such aromatic heterocycles in more applied research fields