Search results for "Antiferromagnet"

Counter-complementarity control of the weak exchange interaction in a bent {Ni(ii)3 complex with a μ-phenoxide-μ-carboxylate double bridge

2019

We have prepared and structurally characterized a novel {Ni3} bent complex bearing a double μ-phenoxide-μ-carboxylate bridge. Both terminal Ni(ii) sites are symmetry related, offering a simplified exchange interaction scheme. DC magnetic data is consistent with a weak antiferromagnetic interaction between the central and terminal Ni(ii) ions. As expected for a Ni(ii) system, local zero-field splitting is observed, which can be experimentally established. Broken symmetry quantum chemical calculations, as well as ab initio CASSCF-SA-SOC computations that support the magnetic experimental data, were also performed. From the analysis of other reported closely related Ni(ii) systems, a counter-c…

Metallosupramolecular compounds based on Cu(ii)/oxalate/twisted NSSN ligands showing a new in situ S–C bond cleavage

2013

Four new complexes, [Cu2(C2O4) 2(SCS)]·3H2O (1), [Cu2(C 2O4)3(SCSH)2]·H2O (2), [Cu(C2O4)(SS)2]·3H2O (3) and [Cu(C2O4)(SS)]·6H2O (4) [where SCS = bis(4-pyridylthio)methane and SS = 4,4′-dipyridyldisulfide], have been synthesized by the reaction of the SS and SCS ligands with the corresponding copper(ii) oxalate salt. The different synthetic conditions allowed control of the preparation of a 3D open metal-organic framework in 1, a dinuclear zwitterionic molecular compound in 2 and one- and two-dimensional (1D and 2D) coordination polymers in 3 and 4, respectively. Compound 4 was also obtained by in situ transformation of the dithioether ligand (SCS) to the disulfide ligand (SS) under hydrothe…

Tailoring the Exchange Interaction in Covalently Linked Basic Carboxylate Clusters through Bridging Ligand Selection

2012

We are reporting new dimeric units of basic carboxylates bearing the {Fe III 2M IIO} motif for M = Co and Ni, covalently bound through the tetradentate bridging (LL) 2,2′-azopyiridine (azpy) and 2,3-di(2-pyridyl)quinoxaline ligands (dpq). We structurally characterized the hexanuclear clusters, and their magnetic properties have been fully analyzed. DFT calculations have been performed as a supplementary tool. All results evidence a weak antiferromagnetic interaction through the bridging ligands between isolated spin ground states arising from intra-Fe 2MO core exchange couplings. Together with the pioneer 2,2′-bipyrimidine bridged systems, the new complexes reported constitute a family of c…

Magnetic excitations of a doped two-dimensional antiferromagnet

1993

Magnetic excitations of the two-dimensional (2D) t-J model are considered in the presence of a small concentration of holes c. The spin-wave approximation used implies long-range antiferromagnetic ordering from the beginning. Migdal's theorem is shown to be valid for the model considered. The energy spectrum of the magnons is determined with the help of the one-pole approximation for the hole Green's function. If the concentration of mobile holes is larger than a critical value an additional branch of overdamped magnons arises near the \ensuremath{\Gamma} and M points of the Brillouin zone. This is connected with the generation of electron-hole pairs (the Stoner excitations) by magnons. The…

Thermal entanglement of a spin-1/2 Ising–Heisenberg model on a symmetrical diamond chain

2011

International audience; The entanglement quantum properties of a spin-1/2 Ising-Heisenberg model on a symmetrical diamond chain were analyzed. Due to the separable nature of the Ising-type exchange interactions between neighboring Heisenberg dimers, calculation of the entanglement can be performed exactly for each individual dimer. Pairwise thermal entanglement was studied in terms of the isotropic Ising-Heisenberg model and analytical expressions for the concurrence (as a measure of bipartite entanglement) were obtained. The effects of external magnetic field H and next-nearest neighbor interaction J(m) between nodal Ising sites were considered. The ground state structure and entanglement …

A rare example of nickel(ii) chains based on a heteroscorpionate-like ligand with quadruple imidazolyl interactions

2014

The first nickel(ii) complex with the heteroscorpionate-like bridging ligand DIMMAL (2-di1H-2-imidazolylmethylmalonate), [Ni(DIMMAL)(H2O)3]n·3nH2O (1), is a one-dimensional coordination polymer whose structure shows regular Ni(ii) chains with H-bonding inter-chain interactions and a rare example of a Quadruple Imidazolyl Embrace (QIE). The Ni(ii) chain shows a weak antiferromagnetic interaction that can be modelled with a regular S = 1 chain model including a zero field splitting with g = 2.270, J = -1.5 cm(-1) and D = -2.26 cm(-1).

Evidences for the Formation of Chromium in the Unusual Oxidation State Cr(IV)

1999

Abstract Magnetic measurements on Tl x Cr 5 Se 8 (0≤ x ≤1) reveal that stoichiometric TlCr 5 Se 8 is a three-dimensional antiferromagnet with a Neel temperature T N of about 55 K. In contrast, samples with a reduced Tl content show highly unusual magnetic properties that are without precedent in the literature of magnetically coupled systems: upon lowering the temperature from 300 K the susceptibility reaches a maximum at about 125 K and then steeply drops to a value comparable to that obtained at room temperature. The height of this maximum increases first with decreasing Tl abundance reaching its largest value at a composition Tl 0.2 Cr 5 Se 8 and then decreases again for samples with x 3…

Alternating Ferro- and Antiferromagnetic Interactions in a Chainlike CuII Coordination Polymer

1993

Synthesis, characterisation, crystal structures, and magnetic properties of one-dimensional oxalato-bridged metal(II) complexes with 3-hydroxypyridin…

2001

One-dimensional oxalato-bridged metal(II) compounds of formula [M(-ox)(L)2]n [L = 3-hydroxypyridine (pyOH) or isoquinoline (isq)] have been synthesised and characterised by FT-IR spectroscopy, TG-DTA techniques, variable-temperature magnetic measurements and X-ray diffraction methods. The complexes [M(-ox)(pyOH)2]n [M= Co (1), Ni (2)] are isomorphous and crystallise in the orthorhombic space group Pnab. The compounds [M(-ox)(isq)2]n [M= Co (3), Ni (4), Cu (5)] are also isomorphous and belong to the monoclinic space group C2/c. Crystal structures consist of zig-zag chains in which cis-[M(L)2] 2 + units are sequentially bridged by bis-bidentate oxalato ligands with intrachain M···M distances …

Unique direct synthesis of cyanide-bridged Fe2Cu2 molecular squares by destruction of sodium nitroprusside

2009

Abstract The one-pot reaction of copper powder, sodium nitroprusside, ammonium thiocyanate and 2,2′-bipyridine (bpy) in acetonitrile solution at ambient conditions of air and water yields the novel heterometallic [Fe2Cu2(bpy)6(μ-CN)4(NCS)2]2[Fe(CN)5(NO)](NCS)2·5H2O complex 1, which has been structurally and magnetically characterized. The most prominent feature of this complex is the unique tetranuclear Fe 2 II Cu 2 II squares comprised [Cu(bpy)NCS]+ and [Fe(bpy)2]2+ corners with CN edges. The Cu⋯Cu and Fe⋯Fe separations are ∼6.72 and ∼7.73 A, respectively. The variable-temperature magnetic susceptibility study revealed that a very weak antiferromagnetic coupling is active between Cu(II) ce…