Yan Suffren

Terbium(III) and Yttrium(III) Complexes with Pyridine-Substituted Nitronyl Nitroxide Radical and Different β-Diketonate Ligands. Crystal Structures and Magnetic and Luminescence Properties

A terbium(III) complex of nitronyl nitroxide free radical 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro1H-imidazolyl-1-oxy-3-oxide (NIT2Py), [Tb(acac)3NIT2Py]·0.5H2O (3) (acac = acetylacetonate), was synthesized for comparison with the previously reported [Tb(hfac)3NIT2Py]·0.5C7H16 (1) (hfac = hexafluoroacetylacetonate), together with their yttrium analogues [Y(hfac)3NIT2Py]·0.5C7H16 (2) and [Y(acac)3NIT2Py]·0.5H2O (4). The crystal structures show that in all complexes the nitronyl nitroxide radical acts as a chelating ligand. Magnetic studies show that 3 like 1 exhibits slow relaxation of magnetization at low temperature, suggesting single-molecule magnet behavior. The luminescence spectra show resolved vibronic structure with the main interval decreasing from 1600 cm(-1) to 1400 cm(-1) between 80 and 300 K. This effect is analyzed quantitatively using experimental Raman frequencies.

RAMAN SPECTROSCOPY OF TRANSITION METAL COMPLEXES: MOLECULAR VIBRATIONAL FREQUENCIES, PHASE TRANSITIONS, ISOMERS, AND ELECTRONIC STRUCTURE

Raman spectroscopy is less commonly used than infrared absorption spectroscopy for the vibrational characterization of inorganic compounds, but its applications have significantly increased over the past decade due to high-performance instrumentation. This Comment describes the use of Raman spectroscopy for the characterization of inorganic compounds. We illustrate the application of Raman techniques with the spectra of a series of classic transition metal complexes recorded at variable temperature and pressure. Illustrative examples include [Ni(NH3)6]X2 compounds (X˭Cl− or [NO3]−), thermochromic square-planar or tetrahedral [CuCl4]2− complexes, the cis and trans [Cu(glycinato)2] · H2O complexes, square-planar [Pt(dithiocarbamate)2] and [Pd(dithiocarbamate)2] complexes, as well as metal-oxo and trans-dioxo complexes of metals with the d2 electron configuration, such as molybdenum(IV), rhenium(V), and osmium(VI). The variation of the symmetric metal-ligand stretching frequencies with temperature or pressure is presented. Resonance Raman spectroscopy provides a detailed characterization of the electronic structure for the [Ru(BQDI)(NH3)2Cl2] complex with the observation of overtones and combination bands at the excitation wavelength of 488 nm. Time-dependent theoretical calculations for the [Ru(BQDI)(NH3)2Cl2] complex are used to rationalize the resonance Raman intensities and to determine excited-state properties. Molecular lanthanide clusters are used to illustrate the applications of Raman spectroscopy to polymetallic complexes.

Tunable trimers:using temperature and pressure to control luminescent emission in gold(i) pyrazolate-based trimers

A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N′)-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N′)-tri-gold(I) (2), tris(μ2-3-methyl-5-phenylpyrazolato-N,N′)-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato-N,N′)-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm−1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.

Room Temperature Magnetic Switchability Assisted by Hysteretic Valence Tautomerism in a Layered Two-Dimensional Manganese-Radical Coordination Framework

The manganese-nitronyl-nitroxide two-dimensional coordination polymer {[Mn2(NITIm)3]ClO4}n (1) (NITImH = 2-(2-imidazolyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-3-oxide-1-oxyl) undergoes an unusual hysteretic thermo-induced valence tautomeric transition near room temperature, during which the manganese(II) ions are oxidized to manganese(III) and two of the three deprotonated radicals (NITIm-) are reduced to their diamagnetic aminoxyl form (denoted NITRed2-). Upon cooling, the high-temperature species {[MnII2(NITIm)3]ClO4}n (1HT) turns into the low-temperature species {[MnIII2(NITRed)2(NITIm)]ClO4}n (1LT) around 274 K, while on heating the process is reversed at about 287 K. This valence tautomeric phenomenon is supported by temperature-dependent magnetic susceptibility measurements, differential scanning calorimetry (DSC), crystal structure determination, UV-vis absorption, X-ray absorption (XAS), and emission (XES) and electron paramagnetic resonance (EPR) spectroscopies in the solid state.

Structures, Thermal Behaviors, and Luminescent Properties of Anhydrous Lanthanum Iodate Polymorphs

The structural and thermal studies of six anhydrous lanthanum iodate polymorphs are presented. The variation of the [IO3(-)]:[La(3+)] molar ratio in the starting solution and the evaporation rate of the solution leads to either the centric La(IO3)3(HIO3) or the acentric La(IO3)3(HIO3)1.33 phases. The crystal structure of La(IO3)3(HIO3)1.33 was determined. The thermal treatments of these two phases up to 490 °C lead to β-La(IO3)3, observed at room temperature. To better understand the similar thermal behaviors of La(IO3)3(HIO3)1.33 and La(IO3)3(HIO3) compounds and their structural evolution, thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC) analyses and in situ temperature-dependent powder X-ray diffraction (XRD) experiments were carried out. These experiments allowed us to highlight the successive formation of δ-La(IO3)3 and γ-La(IO3)3. δ-La(IO3)3 is observed from the beginning of thermal decomposition of La(IO3)3(HIO3)1.33 (at 340 °C) or La(IO3)3(HIO3) (at 300 °C) up to 440 °C. A phase transition from δ-La(IO3)3 to γ-La(IO3)3 then occurs at 440 °C. Finally, the phase transition from γ-La(IO3)3 to β-La(IO3)3 occurs at 140 °C. A cycle of heating and cooling shows the reversible phase transition at 185 and 140 °C, respectively. β-, γ-, and δ-La(IO3)3 are three polymorph phases of the first α-La(IO3)3 already characterized. The structure of β-La(IO3)3 and γ-La(IO3)3 were determined on powder XRD analyses. The iodate compounds present a very broad domain of transparency from the visible range to the beginning of the far-infrared range. The intensities of SHG light generated by α-La(IO3)3, β-La(IO3)3, La(IO3)3(HIO3)1.33, and α-LiIO3 compounds with acentric structures were compared: β-La(IO3)3 < La(IO3)3(HIO3)1.33 < α-La(IO3)3 ≈ α-LiIO3. Finally, the luminescence spectroscopy of La(IO3)3(HIO3)1.33:Nd(3+), α-La(IO3)3:Nd(3+), and α-La(IO3)3:Yb(3+) is studied.

Lanthanide-Based Coordination Polymers with a 4,5-Dichlorophthalate Ligand Exhibiting Highly Tunable Luminescence: Toward Luminescent Bar Codes

Reactions in water of 4,5-dichlorophthalate (dcpa2-) with the heaviest lanthanide ions lead to a family of compounds with the general chemical formula [Ln2(dcpa)3(H2O)5·3H2O]∞, where Ln = Tb-Lu, Y. The synthesis, crystal structure, thermal behavior, and luminescent properties of this series of homonuclear compounds are described. Additionally, this family can be extended to isostructural heteronuclear compounds that can contain some light lanthanide ions and therefore present some original photophysical properties. These compounds show potential interest as multiemissive materials (visible and infrared light between 450 and 1600 nm) and could find application as luminescent bar codes.

Controlling Lanthanide Exchange in Triple‐Stranded Helicates: A Way to Optimize Molecular Light‐Upconversion

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3)3 ]6+ helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3)3 ]6+ is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4)3 ]9+ can be diluted into closed-shell [GaYGa(L4)3 ]9+ matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature.

Optical properties of Nd3+ and Yb3+ -doped metal iodates (AgM(IO3)4): transparent host matrices for mid-IR lasers and nonlinear materials

Nine new isomorphic iodate compounds NaM(IO3)4 with M ¼ Y, Nd, Gd and AgM0(IO3)4 with M0 ¼ Y, La, Nd, Eu, Gd, Bi have been synthesized either by evaporation of concentrated nitric acid solution or by hydrothermal synthesis. They crystallize in the monoclinic acentric Cc space group. Typical unit cell parameters for AgY(IO3)4 are a ¼ 31.277(3) °A, b ¼ 5.547(1) °A, c ¼ 12.556(2) °A, b ¼ 91.11(2) , V ¼ 2178.0(6) °A3 and Z ¼ 8. Crystal structures have been solved on single crystals for NaY(IO3)4, AgY(IO3)4, AgLa(IO3)4, AgGd(IO3)4 and AgBi(IO3)4 and on powder for NaNd(IO3)4, NaGd(IO3)4, AgEu(IO3)4 and AgGd(IO3)4. They are thermally stable up to 550 C for NaY(IO3)4, 430 C for AgY(IO3)4, 500 C for AgLa(IO3)4 and 490 C for AgBi(IO3)4. The crystal structure reveals a two-dimensional layered network. The sheets are connected together by I/O interactions. All these metal iodates generate second harmonics and are transparent up to 12µm. So they are interesting as potential laser matrices in the mid and beginning of the far-infrared. The properties of Nd3+ and Yb3+-doped AgGd(IO3)4 and of Nd3+-doped AgLa(IO3)4 have been studied.

Hexalanthanide Complexes as Molecular Precursors: Synthesis, Crystal Structure, and Luminescent and Magnetic Properties

Reaction of hexanuclear octahedral molecular precursors with a 3-chlorobenzoate ligand affords an unprecedented family of isostructural polylanthanide complexes via solvothermal and microwave-assisted syntheses in an acetonitrile medium. The general chemical formula of the compounds that constitute this series is {[Ln6(μ3-OH)2(H2O)2(NO3)2(3-cb)14]·(CH3CN)4}, where 3-cb- stands for 3-chlorobenzoate and Ln = Eu, Tb, Dy, Ho, Er, or Y. The crystal structure, solubility, and magnetic and luminescent properties of these complexes have been studied. The luminescent properties evidence that the composition of the hexalanthanide precursor is preserved during the synthetic process that is of particular interest for cases in which heterolanthanide complexes are targeted.

Thermodynamic Programming of Erbium(III) Coordination Complexes for Dual Visible/Near-Infrared Luminescence

Intrigued by the unexpected room-temperature dual visible/near-infrared (NIR) luminescence observed for fast-relaxing erbium complexes embedded in triple-stranded helicates, in this contribution, we explore a series of six tridentate N-donor receptors L4-L9 with variable aromaticities and alkyl substituents to extricate the stereoelectronic features responsible for such scarce optical signatures. Detailed solid-state (X-ray diffraction, differential scanning calorimetry, optical spectroscopy) and solution (speciations and thermodynamic stabilities, spectrophotometry, NMR and optical spectroscopy) studies of mononuclear unsaturated [Er(Lk)2 ]3+ and saturated triple-helical [Er(Lk)3 ]3+ model complexes reveal that the stereoelectronic changes induced by the organic ligands affect inter- and intramolecular interactions to such an extent that 1) melting temperatures in solids, 2) the affinity for trivalent erbium in solution, and 3) optical properties in luminescent complexes can be rationally varied and controlled. With this toolkit in hand, mononuclear erbium complexes with low stabilities displaying only NIR emission can be transformed into molecular-based dual Er-centered visible/NIR emitters operating at room temperature in both solid and solution states.