Multiple light-induced NO linkage isomers in the dinitrosyl complex [RuCl(NO)₂(PPh₃)₂]BF₄ nravelled by photocrystallographic and IR analysis

Multiple light-induced reversible metastable NO linkage isomers (PLIs) have been detected in the dinitrosyl compound [RuCl(NO)(2)(PPh3)(2)]BF4 by a combination of photocrystallographic and IR analysis. The IR signature of three PLI states has been clearly identified, with estimated populations of 59% (PLI-1), 8% (PLI-2) and 5% (PLI-3) for a total population of the metastable state of 72%. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. In the ground state, the structure is characterized by a bent and a linear nitrosyl, the bent one being oriented towards the linear equatorial nitrosyl with an Ru-N-O angle of 133.88 (9)degrees. X-ray Fourier difference maps indicate a selectivity of the photo-isomerization process in PLI-1: only the bent NO ligand changes its position, while the linear NO is unaffected. After irradiation at 405 nm, the orientation is changed by rotation towards the Cl ligand opposite the linear NO, with an Ru-N-O angle in this new position of 109 (1)degrees. The photocrystallographic analysis provides evidence that, in the photo-induced metastable state, the bent NO group is attached to the Ru atom through the N atom (Ru-N-O),rather than in an isonitrosyl Ru-O-N binding mode. In the IR spectra, the asymmetric NO vibrational band shifts by -33 cm(-1) to a lower value, whereas the symmetric band splits and shifts by 5 cm(-1) to a higher value and by -8 cm(-1) to a lower value. The down shift is a clear indication of the structural change, and the small upward shift in response to the new electronic configuration of the metastable structure. Variable-temperature IR kinetic measurements in the range 80-114 K show that the decay of the PLI-1 state follows an Arrhenius behaviour with an activation energy of 0.22 eV

Structural and comparative study of water confined in a mesoporous bioglass by X-ray total scattering

International audienceThe structural properties of water confined in two silica matrices characterised by well-controlled organised porosity with a narrow pore size distributioni)a new mesoporous bioactive glass (MBG 92S6) andii)SiO2 MCM-41 were studied using laboratory total X-ray scattering coupled to molecular pair distribution function (PDF). The PDF analysis shows that the hydrophilic/hydrophobic character of the water-bioglass interface affects the structural properties of the confined water in the same way as water confined in different mesoporous matrices presenting an intermediate hydrophilic and hydrophobic interface regardless of their pore size and distribution. We also compare the effect of the confinement inside MBG 92S6 and different mesoporous hydrophilic and hydrophobic silica matrices. We show that the pore surface properties have a stronger influence on the structural organisation of the confined water than the pore size distribution

Multimetastability, phototrapping, and thermal trapping of a metastable commensurate superstructure in a FeII spin-crossover compound

The photoinduced switching and subsequent relaxation regime at cryogenic temperatures of the two-step spin-crossover compound [Fe(bapbpy)(NCS) 2] has been investigated by time-dependent photocrystallography. Upon photoexcitation from the low-spin (LS) state, a direct population of the metastable high-spin (HS) state occurs, without involving any intermediate structural state. The relaxation from the metastable HS state in isothermal conditions at 40K proceeds in two successive steps associated with two symmetry breaking processes. The first step corresponds to the cooperative transformation to an intermediate superstructure, characterized by a long-range-ordered [HS-LS-LS] motif coupled to a commensurate displacive modulation, and concomitant with a tripling of the c axis of the unit cell (C2/c space group). The stabilization of the intermediate state is driven by strong molecule-lattice coupling. In the second stage, the intermediate state undergoes a transformation twinning triggered by lattice strain towards the LS state. The two-step relaxation is reminiscent of the two-step thermal transition of [Fe(bapbpy)(NCS) 2] and evidences multimetastability in the light-induced or relaxation regime. The long-range-ordered [HS-LS-LS] superstructure has also been trapped by rapid quench cooling to very low temperature, and has been structurally characterized. © 2012 American Physical Society

Photocrystallography and IR spectroscopy of light-induced linkage NO isomers in [RuBr(NO)(2)(PCyp(3))(2)]BF4

International audienceOne single photo-induced linkage NO isomer (PLI) is detected and characterized in the dinitrosyl pentacoordinated compound [RuBr(NO)(2)(PCyp(3))(2)]BF4 by a combination of photocrystallographic and IR analysis. In the ground state, the molecule adopts a trigonal-bipyramidal structure with the two NO ligands almost linear with angles Ru-N1-O1 = 168.92 (16), Ru-N2-O2 = 166.64 (16)degrees, and exactly equal distances of Ru-N = 1.7838 (17) and O-N = 1.158 (2) angstrom. After light irradiation of 405 nm at T = 10 K, the angle of Ru-N2-O2 changes to 114.2 (6)degrees by rotation of the O atom towards the Br ligand with increased distances of Ru-N2 = 1.992 (6) and N2-O2 = 1.184 (8) angstrom, forming a bent kappa N bonded configuration. Using IR spectroscopy, the optimal wavelength and maximum population of 39 (1)% of the PLI is determined. In the ground state (GS), the two symmetric nu(s)(NO) and asymmetric nu(as)(NO) vibrations are measured at 1820 and 1778 cm(-1), respectively. Upon photo-irradiation, the detection of only one new vibrational nu(NO) stretching band at 1655 cm(-1), assigned to the antisymmetric coupled vibration mode and shifted to lower wavenumbers by -123 cm(-1), supports the photocrystallographic result. These experimental results are supported by additional DFT calculations, which reproduce the structural parameters and vibrational properties of both the ground state and the photo-induced linkage isomer well. Especially the experimentally characterized molecular structure of the PLI state corresponds to an energy minimum in the calculations; the stabilization of the bent kappa N bonded configuration of the PLI state originates from specific intramolecular orbital overlap

Management of severe malarial infection.

Severe malaria is a major cause of infant and childhood death in the tropics. Effective management relies on rapid diagnosis, prompt administration of parenteral schizonticidal antimalarial drugs, careful fluid balance, prevention of convulsions and early recognition of complications such as hypoglycemia, metabolic acidosis, anemia, pulmonary edema, renal failure, bleeding and supervening bacterial sepsis. The mortality of treated cerebral malaria remains 20%. New, more rapidly acting antimalarials and earlier referral of children with complicated infections should reduce this unacceptable death rate

Imprinting isolated single iron atoms onto mesoporous silica by templating with metallosurfactants

International audienceHypothesisOne of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts.ExperimentsHerein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio.FindingsThe fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones