33 research outputs found
Photoinduced Oxygen Evolution Catalysis Promoted by Polyoxometalate Salts of Cationic Photosensitizers
The insoluble salt Cs15K[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] (CsCo9) is tested as heterogeneous oxygen evolution catalyst in light-induced experiments, when combined with the homogeneous photosensitizer [Ru(bpy)3]2+ and the oxidant Na2S2O8 in neutral pH. Oxygen evolution occurs in parallel to a solid transformation. Post-catalytic essays indicate that the CsCo9 salt is transformed into the corresponding [Ru(bpy)3]2+ salt, upon cesium loss. Remarkably, analogous photoactivated oxygen evolution experiments starting with the [Ru(bpy)3](5+x)K(6−2x)[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3]·(39+x)H2O (RuCo9) salt demonstrate much higher efficiency and kinetics. The origin of this improved performance is at the cation-anion, photosensitizer-catalyst pairing in the solid state. This is beneficial for the electron transfer event, and for the long-term stability of the photosensitizer. The latter was confirmed as the limiting process during these oxygen evolution reactions, with the polyoxometalate catalyst exhibiting robust performance in multiple cycles, upon addition of photosensitizer, and/or oxidant to the reaction mixture
Mössbauer thermal scan study of a spin crossover system
Programmable Velocity equipment was used to perform a Mössbauer Thermal Scans to allow a quasi-continuous temperature study of the magnetic transition between the low-spin and a high-spin configurations in [Fe(Htrz)2(trz)](BF4) system. The material was studied both in bulk as in nanoparticles sample forms.Facultad de Ciencias ExactasInstituto de Física La PlataInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
Mössbauer thermal scan study of a spin crossover system
Programmable Velocity equipment was used to perform a Mössbauer Thermal Scans to allow a quasi-continuous temperature study of the magnetic transition between the low-spin and a high-spin configurations in [Fe(Htrz)2(trz)](BF4) system. The material was studied both in bulk as in nanoparticles sample forms.Facultad de Ciencias ExactasInstituto de Física La PlataInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
Enforcing Multifunctionality: A Pressure-Induced Spin-Crossover Photomagnet
Photomagnetic compounds are usually
achieved by assembling preorganized
individual molecules into rationally designed molecular architectures
via the bottom-up approach. Here we show that a magnetic response
to light can also be enforced in a nonphotomagnetic compound by applying
mechanical stress. The nonphotomagnetic cyano-bridged Fe<sup>II</sup>–Nb<sup>IV</sup> coordination polymer {[Fe<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>FeNb</b>) has been
subjected to high-pressure structural, magnetic and photomagnetic
studies at low temperature, which revealed a wide spectrum of pressure-related
functionalities including the light-induced magnetization. The multifunctionality
of <b>FeNb</b> is compared with a simple structural and magnetic
pressure response of its analog {[Mn<sup>II</sup>(pyrazole)<sub>4</sub>]<sub>2</sub>[Nb<sup>IV</sup>(CN)<sub>8</sub>]·4H<sub>2</sub>O}<sub><i>n</i></sub> (<b>MnNb</b>). The <b>FeNb</b> coordination polymer is the first pressure-induced spin-crossover
photomagnet
Temperature- and Light-Induced Spin Crossover Observed by X-ray Spectroscopy on Isolated Fe(II) Complexes on Gold
Using X-ray absorption techniques, we show that temperature- and light-induced spin crossover properties are conserved for a submonolayer of the [Fe(H2B(pz)2)2(2,2′-bipy)] complex evaporated onto a Au(111) surface. For a significant fraction of the molecules, we see changes in the absorption at the L2,3 edges that are consistent with those observed in bulk and thick film references. Assignment of these changes to spin crossover is further supported by multiplet calculations to simulate the X-ray absorption spectra. As others have observed in experiments on monolayer coverages, we find that many molecules in our submonolayer system remain pinned in one of the two spin states. Our results clearly demonstrate that temperature- and light-induced spin crossover is possible for isolated molecules on surfaces but that interactions with the surface may play a key role in determining when this can occur
Photoinduced Oxygen Evolution Catalysis Promoted by Polyoxometalate Salts of Cationic Photosensitizers
Radical salts of TTF derivatives with the metal-metal bonded [Re2Cl8]2- anion
International audienc
New paramagnetic Re(II) compounds with nitrile and cyanide ligands prepared by homolytic scission of dirhenium complexes
The preparation and characterization of three new paramagnetic complexes of the 17-electron ReII ion are reported. The salts [Re(triphos)(CH3CN)3)][X]2, X = [BF4]- (1), [PF6]- (2), and [Et4N][Re(triphos)(CN)3] (3) were prepared by homolytic cleavage of the Re−Re bond in [Re2(CH3CN)10][BF4]4 or by disruption of the chlorine bridges in [(triphos)Re(μ-Cl)3Re(triphos)]Cl (1) (triphos = 1,1,1-tris(diphenylphosphino-methyl)ethane) and characterized by single-crystal X-ray diffraction, infrared and 1H NMR spectroscopies, cyclic voltammetry, and magnetic susceptibility measurements. Compound 2 undergoes reversible reduction and irreversible oxidation processes while 3 undergoes a reversible reduction, an irreversible oxidation, and a reversible oxidation. The magnetic susceptibility data for 2 and 3 exhibit a strong temperature independent paramagnetic component which is in accord with a highly anisotropic S = 1/2 magnetic ground state. The results of this study indicate that dinuclear Re2II,II starting materials are viable precursors for producing unusual mononuclear ReII complexes
Self-assembly of a High-Nuclearity Chloride-Centered Copper(II) Cluster. Structure and Magnetic Properties of [Au(PPh3)2][trans-Cu6(m-OH)6{m-(3,5-CF3)2pz}6Cl.
A chloride-centered hexanuclear copper(II) pyrazolate [Au(PPh3)2]-[trans-Cu6(μ-OH)6{μ-(3,5-CF3)2pz}6Cl] is isolated from the reaction of the trinuclear copper(I) pyrazolate [Cu3{μ-(CF3)2pz}3] with PPh3AuCl and Ph3P in moist air. The six copper atoms are bridged by pyrazolate and hydroxyl ligands, above and below the copper plane. The chloride anion exists at the center of the planar cavity formed by the copper atoms with Cu-Cl distances of 3.02-3.13 Å. The magnetic susceptibility measurements show a strong antiferromagnetic coupling between the copper centers with an estimated exchange constant of J ~ 650 cm-1
Brief encounter at the molecular level: what muons tell us about molecule-based magnets
Spin-polarized muons can be implanted in various molecular magnetic materials in order to measure static and dynamic magnetic field distributions at a local level. The positively-charged muon is an unstable, radioactive particle which has spin-1/2, a lifetime of 2.2 mu s, about one-ninth of the proton mass and a magnetic moment of approximately 1/200 mu(B). Both pulsed and continuous beams of muons can be produced with almost 100% spin polarization and significant intensity at various accelerator facilities. The subsequent decay of the muon into a positron allows the extraction of the muon-spin autocorrelation function which can be related to the magnetic field distribution inside a sample. This experimental technique has found particular application to the problem of hydrogen in semiconductors, as well as the study of the vortex lattice in both high-temperature and organic superconductors. Nevertheless, it has been most widely employed in the field of magnetism. We describe how our experiments using spin-polarized muons have been used to provide information about organic ferromagnets, molecular magnets, spin-chains and single molecule magnets