Marcello Mazzani

Four μ4-oxo-bridged copper(II) complexes: magnetic properties and catalytic applications in liquid phase partial oxidation reactions

Four copper(II) complexes, [Cu(4)(O)(L(n))(2)(CH(3)COO)(4)] with N(2)O-donor Schiff-base ligands, where HL(1) = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)phenol for complex 1, HL(2) = 4-methyl-2,6-bis(phenylmethyliminomethyl)phenol for complex 2 x CH(3)CN, HL(3) = 4-methyl-2,6-bis(((3-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 3, HL(4) = 4-methyl-2,6-bis(((4-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 4, were synthesized and characterized by elemental analysis, FT-IR, UV-vis spectroscopy and finally by single crystal X-ray diffraction study. X-Ray analysis reveals that all of these are mu(4)-oxo-bridged tetrameric copper(II) complexes. Four copper atoms arrange themselves around an oxygen atom tetrahedrally. Magnetic susceptibility measurements show the existence of very strong antiferromagnetic coupling among these ions (J = -210.1 to -271.3 cm(-1)), mediated by the oxygen atoms. Catalysis of the epoxidation of cyclohexene, styrene, alpha-methylstyrene and trans-stilbene by these complexes has been carried out homogeneously as well as heterogeneously by immobilizing the metal complexes over 2D-hexagonal mesoporous silica. The results obtained in both the catalytic conditions show that the olefins are converted to the respective epoxides in good yield together with high selectivity.

Muons Probe Strong Hydrogen Interactions with Defective Graphene

Here, we present the first muon spectroscopy investigation of graphene, focused on chemically produced, gram-scale samples, appropriate to the large muon penetration depth. We have observed an evident muon spin precession, usually the fingerprint of magnetic order, but here demonstrated to originate from muon-hydrogen nuclear dipolar interactions. This is attributed to the formation of CHMu (analogous to CH(2)) groups, stable up to 1250 K where the signal still persists. The relatively large signal amplitude demonstrates an extraordinary hydrogen capture cross section of CH units. These results also rule out the formation of ferromagnetic or antiferromagnetic order in chemically synthesized graphene samples.

Magnetic Behavior of Odd- and Even-Electron Metal Carbonyl Clusters: The Case Study of [Co8Pt4C2(CO)24]n− (n = 1, 2) Carbide Cluster

The reaction of [Co(6)C(CO)(15)](2-) with 2 equiv of PtCl(2)(Et(2)S)(2) affords the new heterobimetallic [Co(8)Pt(4)C(2)(CO)(24)](2-), [1](2-), carbonyl cluster. [1](2-) undergoes reversible chemical and electrochemical oxidation and reduction processes disclosing a complete series of [1](n-) (n = 1-4) clusters. The mono- and dianion of [1](n-) have been isolated as their tetra-substituted ammonium salts and fully characterized by means of IR, (13)C NMR, ESI-MS, and X-ray crystallography. Variable-temperature (VT) solid-state EPR studies on pure crystalline samples indicate that both [1](2-) and [1](-*) are paramagnetic, due to a doublet state of the latter and a triplet state of [1](2-). This conclusion is supported by SQUID measurements on the same crystalline sample of [1](2-). The present study indisputably demonstrates that even-electron transition metal carbonyl clusters (TMCC) can be magnetic.

Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)

We investigate the effect of external pressure on magnetic order in undoped LnFeAsO (Ln =La, Ce, Pr, Sm) by using muon spin relaxation measurements and ab initio calculations. Both the magnetic transition temperature Tm and the Fe magnetic moment decrease with external pressure. The effect is observed to be lanthanide dependent, with the strongest response for Ln = La and the weakest for Ln = Sm. The trend is qualitatively in agreement with our density functional theory calculations. The same calculations allow us to assign a value of 0.68(2) μB to the Fe moment, obtained from an accurate determination of the muon sites. Our data further show that the magnetic lanthanide order transitions do not follow the simple trend of Fe, possibly as a consequence of the different f-electron overlap.

Common effect of chemical and external pressures on the magnetic properties of RCoPO (R = La, Pr, Nd, Sm). II.

G. Prando, ∗ P. Bonfà, G. Profeta, R. Khasanov, F. Bernardini, M. Mazzani, E. M. Brüning, A. Pal, V. P. S. Awana, H.-J. Grafe, B. Büchner, 7 R. De Renzi, P. Carretta, and S. Sanna Leibniz-Institut für Festkörperund Werkstoffforschung (IFW) Dresden, D-01171 Dresden, Germany Dipartimento di Fisica and Unità CNISM di Parma, Università di Parma, I-43124 Parma, Italy Department of Physical and Chemical Sciences and SPIN-CNR, Università dell’Aquila, I-67100 L’Aquila, Italy Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland IOM-CNR and Dipartimento di Fisica, Università di Cagliari, I-09042 Monserrato (Ca), Italy National Physical Laboratory (CSIR), New Delhi 110012, India Institut für Festkörperphysik, Technische Universität Dresden, D-01062 Dresden, Germany Dipartimento di Fisica and Unità CNISM di Pavia, Università di Pavia, I-27100 Pavia, Italy (Dated: May 6, 2014)

The structural and electronic evolution of Li4C60 through the polymer–monomer transformation

In this paper, we combine synchrotron powder x-ray diffraction, 7Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li4C60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR, however, reveals the presence of intrinsic centers originating from broken C60–C60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7Li NMR shift. At low temperatures, the Li+ ions are statically disordered on the 7Li NMR timescale. The observed 7Li NMR line narrowing at T>200 K is ascribed to the Li+ diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ~470 K results in gradual depolymerization to the metallic monomer fcc high temperature structure. The transformation is first order and polymer as well as monomer phases coexist over a broad temperature interval (130 K).

Recovering metallicity in A 4 C 60 : The case of monomeric Li 4 C 60

The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T > 600 K, show that its fcc structure is associated with a complete (4e) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination. Moreover, they suggest the present system as a potential precursor to a new class of superconducting fullerides.

Stripe disorder and dynamics in the hole-doped antiferromagnetic insulator La5/3Sr1/3CoO4

We investigate the magnetic ordering and dynamics of the stripe phase of La 5/3 Sr 1/3 CoO 4 , a material shown to have an hourglass magnetic excitation spectrum. A combination of muon-spin relaxation, nuclear magnetic resonance, and magnetic susceptibility measurements strongly suggest that the physics is determined by a partially disordered configuration of charge and spin stripes whose frustrated magnetic degrees of freedom are dynamic at high temperature and which undergo an ordering transition around 35 K with coexisting dynamics that freeze out in a glassy manner as the temperature is further reduced.

Onset of magnetism in optimally electron-doped LFe1−xRuxAsO1− yFy (L= La, Nd, or Sm) superconductors around x=1/4

S. Sanna, 1 P. Carretta, 1 R. De Renzi, 2 G. Prando, 1,3 P. Bonfá, 2 M. Mazzani, G. Lamura, T. Shiroka, 5,6 Y. Kobayashi, 7 M. Sato 7 1 Department of Physics, University of Pavia-CNISM, I-27100 Pavia, Italy 2 Department of Physics and Earth Sciences, University of Parma-CNISM, I-43121 Parma, Italy 3 Leibniz-Institut für Festkörperund Werkstoffforschung (IFW) Dresden, D-01171 Dresden, Germany 4 CNR-SPIN and Universitá di Genova, via Dodecaneso 33, I-16146 Genova, Italy 5 Laboratorium für Festkörperphysik, ETH-Hönggerberg, CH-8093 Zürich, Switzerland 6 Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland and 7 Department of Physics, Division of Material Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan (Dated: May 11, 2014)

Muons probe magnetism and hydrogen interaction in graphene

Muon spin resonance (μSR) is a powerful technique for investigating the local magnetic fields in materials through implanted muons. Here we report a μSR study of chemically produced thermally exfoliated graphene. Our results provide an experimental answer to the many theoretical investigations of magnetic properties of graphene. The observed muon spin precession is attributed to a localized muon–hydrogen nuclear dipolar interaction rather than to a hyperfine interaction with magnetic electrons. This proves the absence of magnetism in chemically produced thermally exfoliated graphene.