170 research outputs found
Field-induced level crossings in spin clusters: Thermodynamics and magneto-elastic instability
Quantum spin clusters with dominant antiferromagnetic Heisenberg exchange
interactions typically exhibit a sequence of field-induced level crossings in
the ground state as function of magnetic field. For fields near a level
crossing, the cluster can be approximated by a two-level Hamiltonian at low
temperatures. Perturbations, such as magnetic anisotropy or spin-phonon
coupling, sensitively affect the behavior at the level-crossing points. The
general two-level Hamiltonian of the spin system is derived in first-order
perturbation theory, and the thermodynamic functions magnetization, magnetic
torque, and magnetic specific heat are calculated. Then a magneto-elastic
coupling is introduced and the effective two-level Hamilitonian for the
spin-lattice system derived in the adiabatic approximation of the phonons. At
the level crossings the system becomes unconditionally unstable against lattice
distortions due to the effects of magnetic anisotropy. The resultant
magneto-elastic instabilities at the level crossings are discussed, as well as
the magnetic behavior.Comment: 13 pages, 8 figures, REVTEX
[S-Allyl-4-(4-hydroxy-2-oxidobenzylidene-κO)-1-(2-oxidobenzylidene-κO)isothiosemicarbazidato-κ2 N 1,N 4](ethanol-κO)dioxidouranium(VI) ethanol monosolvate
In the title compound, [U(C18H15N3O3S)O2(C2H5OH)]·C2H5OH, the UVI ion is in a distorted pentagonal–bipyramidal coordination geometry, with two oxide O atoms in axial sites. Two N and two O atoms of the tetradentate ligand and an O atom of an ethanol ligand form the equatorial plane. The dihedral angle between the mean planes of the two benzene rings is 34.8 (3)°. In the crystal, relatively strong O—H⋯O hydrogen bonds connect the complex and ethanol solvent molecules into alternating centrosymmetric R
2
2(8) and R
4
4(16) ring motifs, forming chains along [100]. Weak intermolecular C—H⋯O hydrogen bonds are also present
(4Z,6Z,12Z,14Z)-2,10-Dimethyl-2,8,10,16-tetrahydrodipyrazolo[3,4-e:3′,4′-l][1,2,4,8,9,11]hexaazacyclotetradecine-4,12-diamine
The title compound, C12H16N12, is a centrosymmetric molecule which comprises of a hexaaza[14]annulene macrocyclic ring fused with two pyrazole rings. The macrocyclic ring is essentially planar, with an r.m.s. deviation of 0.0381 Å. The electron pairs of the amino groups are delocalized with the conjugated system of the macrocycle. Strong intramolecular N—H⋯N hydrogen bonds arranged in an S
2
2(10) graph-set motif are present in the macrocyclic ring. In the crystal, the amino groups act as donors for intermolecular N—H⋯N interactions with the N atoms of the heterocyclic system, forming a network of two types of extended chains oriented parallel to the [101] and [011] directions. The crystal packing is also stabilized by weak intermolecular C—H⋯N hydrogen bonds formed between pyrazole C—H groups and N atoms of the macrocyclic ring, running in the [10] direction
Magnetothermal properties of molecule-based materials
We critically review recent results obtained by studying the low-temperature
specific heat of some of the most popular molecular magnets. Perspectives of
this field are discussed as well.Comment: 12 pages text + 14 pages figures, Submitted as "feature article" to
Journal of Materials Chemistr
Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering
Molecular nanomagnets are among the first examples of spin systems of finite
size and have been test-beds for addressing a range of elusive but important
phenomena in quantum dynamics. In fact, for short-enough timescales the spin
wavefunctions evolve coherently according to the an appropriate cluster
spin-Hamiltonian, whose structure can be tailored at the synthetic level to
meet specific requirements. Unfortunately, to this point it has been impossible
to determine the spin dynamics directly. If the molecule is sufficiently
simple, the spin motion can be indirectly assessed by an approximate model
Hamiltonian fitted to experimental measurements of various types. Here we show
that recently-developed instrumentation yields the four-dimensional
inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal
space and enables the spin dynamics to be determined with no need of any model
Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to
demonstrate the potential of this new approach. For the first time we extract a
model-free picture of the quantum dynamics of a molecular nanomagnet. This
allows us, for example, to examine how a quantum fluctuation propagates along
the ring and to directly test the degree of validity of the
N\'{e}el-vector-tunneling description of the spin dynamics
Binding CO2 by a Cr8 Metallacrown.
The {Cr8 } metallacrown [CrF(O2 C(t) Bu)2 ]8 , containing a F-lined internal cavity, shows high selectivity for CO2 over N2 . DFT calculations and absorption studies support the multiple binding of F-groups to the C-center of CO2 (C⋅⋅⋅F 3.190(9)-3.389(9) Å), as confirmed by single-crystal X-ray diffraction
A Facile Synthetic Route to a Family of Mn(III) Monomers and their Structural, Magnetic and Spectroscopic Studies
This is an accepted manuscript of an article published by Wiley in European Journal of Inorganic Chemistry on 07/10/2016, available online: https://doi.org/10.1002/ejic.201601124
The accepted version of the publication may differ from the final published version.© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We report a rapid and facile route to the synthesis of a family of MnIIImonomers of general formula [MnIIIF3(H2O)(L1–6)]·xH2O·yMeOH [L1= 2,2′-bipyridyl, x = 2, y = 0 (1′); L2= 1,10′-phenanthroline, x = y = 0 (2′); L3= 6-methyl-2,2′-dipyridyl, x = y = 0 (3), L4= 4,4-dimethyl-2,2′-dipyridyl, x = 2, y = 0 (4), L5= 5,5′-dimethyl-2,2′-dipyridyl, x = 0, y = 0.5 (5); L6= 5-chloro-1,10-phenanthroline, x = y = 0 (6)]. Magnetic susceptibility and magnetisation experiments have been employed to elucidate the D tensor for each family member (ranging from –3.01 cm–1in 2′ to –4.02 cm–1in 5), while multi-frequency/high-field EPR spectroscopic measurements and subsequent simulations gave similar values for complexes 1′ (–4.25 cm–1), 2′ (–4.03 cm–1), 4 (–3.90 cm–1) and 5 (–4.04 cm–1). The terminal Mn–F vibrational stretches in 1′–6 have been probed using Raman spectroscopy.The authors would like to thank the Irish Research Council for Science, Engineering and Technology (IRSCET) Embark Fellowship (E. H.) and the Engineering and Physical Sciences Research Council (EPRSC) (S. S. and E. K. B.) for funding.Published versio
Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties
Synthesis and Characterization of Chiral Tetraaza Macrocyclic Nickel(II) and Palladium(II) Complexes
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