1,721,170 research outputs found
Single-molecule Magnets Based on Iron(III) Oxo Clusters
No full textPolynuclear compounds of magnetic transition metal ions are attracting large interest after the discovery that their magnetisation may relax very slowly at low temperature. Since their behaviour is similar to that of bulk magnets they may be called single molecule magnets. Here we review the magnetic properties of iron(III) clusters showing such features which may be interesting for future applications, as well as strategies for designing new molecules with increased performances
Valence Tautomerism in a Cobalt Complex of a Schiff Base Diquinone Ligand
No full textThe cobalt(III) complex of a Schiff base diquinone ligand Co-III(Cat-N-BQ)(Cat-N-SQ) undergoes an entropy-driven valence tautomeric equilibrium in solution yielding the Co-II(Cat-N-BQ)(2) species. This suggestion is supported by variable temperature electronic and H-1 NMR spectra, as well as by solution magnetic susceptibility data. The calculated thermodynamic quantities associated to the redox equilibrium are Delta H = 42.0(0.8) kJ mol(-1) and Delta S = 140 (3) J mol(-1) K-1
A Cyclic Hexairon(III) Complex with an Octahedrally Coordinated Sodium Ion at the Center, an Example of the [12]Metallacrown–6 Structure Type
No full text[NaFe6(OMe)12(dbm)6]Cl·12MeOH·CHCl3 (I; dbmH = dibenzoylmethane) was prepd. and characterized by elemental anal., spectral (UV, IR), x-ray crystallog., and magnetic methods. The 6 Fe atoms are located at the vertexes of an almost regular hexagon, with Fe···Fe sepns. in the range 3.18-3.20 Å and vertex angles of 119.5-120.5°. The ring serves as a host for the Na ion. Antiferromagnetic exchange coupling interactions exist between the paramagnetic Fe(III) centers (J = 20 cm-1). I is a good structural model for cyclic intermediates proposed for the polyalc.-promoted hydrolysis of Fe(III) salts
Magnetic Exchange Coupling in the FeIII6(μ6-O) Core: A Hint to the Magnetic Properties of Higher-Nuclearity Spin Clusters
No full textVariable-temperature magnetic susceptibility measurements performed on two hexairon(III) clusters containing a μ6-oxo bridge show that this unusual bridging mode leads to weak antiferromagnetic exchange-coupling interactions between the metal centers, with J(trans) and J(cis) values of 19(2) and 9(1) cm-1, respectively. The result is relevant to the search for magneto-structural correlations in oxo-bridged polyiron aggregates
New Experimental Techniques for Magnetic Anisotropy in Molecular Materials
No full textMagnetic anisotropy is a very important property in magnetochemistry. Its knowledge allows us to obtain a fundamental understanding of the electronic structure of both simple paramagnetic species and of magnetically coupled systems. The difficulties associated with its experimental determination have so far limited its investigation. Recently new experimental techniques using superconducting quantum interference devices (SQUID) and micro-SQUID arrays as well as cantilever torque magnetometry have drastically reduced the size of the crystals needed for the measurements, thus opening new perspectives. We will briefly review here these techniques, with the aim to advertise their use in the chemical community
Spintronics: The molecular way
No full textAn invited Meeting Report on the first European Conference on Molecular Spintronics, held in Bologna (Italy)
Single-molecule Magnets on Surfaces
No full textEncoding and manipulating information through the spin degrees of freedom of individual magnetic molecules or atoms is one of the central challenges in the continuing trend towards molecular/atomic scale electronics. With their large magnetic moment and long spin relaxation time, single-molecule magnets (SMMs) are of special importance in this emerging field. Their electrical addressing at the molecular level appears now well within reach using STM methods, which require to organize SMMs on a conducting surface. In this chapter, we present a critical overview of the latest achievements in the deposition of SMMs as monolayers or submonolayers on native or prefunctionalized surfaces. Special emphasis is placed on the selection and design of molecular structures that withstand solution or vapour-phase processing and that maintain their magnetic functionality on a surface. Chemical strategies to control the strength of molecule–substrate interaction and the molecular orientation on the surface are also illustrated. Rewardingly, these efforts have shown that the distinctive properties of SMMs, i.e. slow spin relaxation and quantum tunnelling of the magnetic moment, persist in metal-wired molecules
Low-temperature specific heat of Fe-6 and Fe-10 molecular magnets
No full textThe energy splitting of the low-lying levels has been investigated on two magnetic molecular clusters Fe-6 and Fe-10 by means of low-temperature zero-field specific-heat measurements. Significant deviations from the usual C similar to T-2 law were observed above the maximum of the main Schottky anomalies as a result of nonnegligible contributions from the excited spin states with S>1 and the estimated lattice contributions follow a phenomenological power law C/R similar to T-alpha with alpha-2.7 for both these compounds. The singlet-triplet energy gaps evaluated by the Schottky anomaly, T-0=19.2 K for Fe6 and 4.56 K for Fe-10, are smaller than what we can estimate by a simplified spin-Hamiltonian approach in the strong exchange approximation and using the energy levels obtained by the high-field magnetization and susceptibility measurements. This discrepancy asks for a more complex description of the low-lying states of these molecular clusters, beyond the strong exchange approximation. At very low temperatures T<<1 K, two low-energy Schottky anomalies were also observed in Fe-10, probably due to a small fraction of defected rings or to hyperfine contributions
Structure of catena–(2–Amino–1,3,4–Thiadiazolium, 2–Amino–1,3,4–Thiadiazole bis(mu–Iodo)–di–Iodo–Bismuth(III))
No full text[(C2H4N3S) (C2H3N3S) BiI4]infinity; [(HL) (L) BiI4]infinity (L = 2-amino-1,3,4-thiadiazole), M(r) = 919.86, monoclinic, P 1 2(1)/a 1, a = 7.622(1), b = 18.977(2), c = 12.821(1)angstrom, beta = 102.77(1)-degrees, final R = 0.033. The crystals consist of HL+ cations, neutral L molecules and polymeric [BiI4]infinity- anions built up of edge-sharing [BiI6]3- octahedra, with Bi-I(bridging) distances in the range 3.320(1)-3.057(1) angstrom and Bi-I(terminal) distances in the range 2.917(1)-2.929(1)angstrom. The H-1 and C-13 spectra in DMSO-d6 solution are used in conjunction with the X-Ray structural results to establish the preferred protonation site of the thiadiazole ring
Magnetic Anisotropy of Fe6 and Fe10 Molecular Rings by Cantilever Torque Magnetometry in High Magnetic Fields
No full textWe studied the magnetic anisotropy of 2 mol. magnets, Fe6 and Fe10, which comprise 6- and 10-membered rings of antiferromagnetically coupled Fe (III) ions (Si = 5/2), resp. Spin-flip transitions induced by the applied magnetic field (≤23 T) were investigated by cantilever torque magnetometry on microgram single crystals at very low temp. (down to 0.45 K). From the sharp, steplike variations of magnetic anisotropy at the transition fields, we detd. the singlet-triplet energy gap (Δ1) and the axial zero-field splitting parameter (D1) for the triplet state of Fe6 [Δ1 = 15.28(1) cm-1, D1 = 4.32(3) cm-1] and Fe10 [Δ1 = 4.479(4) cm-1, D1 = 2.24(2) cm-1]. By analyzing the addnl. steps obsd. in the Fe10 sample, we evaluated the ΔS and DS parameters for the total-spin multiplets with S ≤5. On the basis of our findings, we discuss the origin of magnetic anisotropy in Fe(III) rings and the application of torque magnetometry to the study of field-induced level crossing in mol. magnets
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