The zero-field susceptibilities parallel and perpendicular to the tetragonal axis of NiCl2⋅4SC(NH2)2 have been measured between 1.2 and 30 K and fitted to the usual spin Hamiltonian. The resulting parameters are D/kB = 7.6±0.4 K, z0J/kB = −4.5±0.3 K, g∥ = 2.26±0.03 and g⊥ = 2.34±0.03. The susceptibility has also been measured parallel to the tetragonal axis at constant temperatures between 0.3 and 2 K as a function of external field. Magnetic ordering is found to occur, and portions of the phase boundary between paramagnetic and antiferromagnetic states have been determined.
2 Cl 2 ]X 2 ·nH 2 O preparada como sais perclorato 3, nitrato 4 e cloreto 5, respectivamente, foram isoladas e caracterizadas por técnicas espectroscópicas (UV/Vis, IV e EPR). O composto 2 teve sua estrutura determinada por cristalografia de raios-X. Em solventes não-aquosos predomina a espécie dinuclear, enquanto em solução aquosa, ou solventes contendo água, um equilíbrio entre a espécie dinuclear e a mononuclear 1 foi observado. Estudos cinéticos, em metanol, da oxidação catalisada de TMPD indicaram uma dependência de primeira-ordem da velocidade inicial com a concentração de catalisador e um efeito de saturação com aumento da concentração de substrato. O composto dinuclear é mais reativo que o mono-, e experimentos adicionais mostraram que o contra-íon cloreto afeta significativamente os parâmetros cinéticos, deslocando o equilíbrio envolvendo as espécies 2 e 5, além de estabilizar um par iônico com o substrato.Some new copper(II) complexes with a tridentate imine ligand, bimpy (or 2-(benzimidazolyl)methylene-2-amino-1-ethylpyridine), were prepared, and had their catalytic activity in the N,N,N´,N´-tetramethyl-p-phenylenediamine (TMPD) oxidation compared. Mononuclear species, [Cu(bimpy)(H 2 O) 2 ](NO 3 ) 2 , (1) and [Cu(bimpy)Cl 2 ]·H 2 O, (2), as well as the dinuclear species containing chloro-bridges, [Cu 2 (bimpy) 2 Cl 2 ]X 2 ·nH 2 O as perchlorate 3, nitrate 4 and chloride 5 salts, respectively, were obtained and characterized by different techniques (UV/Vis, IR, EPR and X-ray crystallography). In non-aqueous solvents, the dinuclear species predominates; however, in aqueous solution or solvents containing water, equilibrium between dinuclear and correlated mononuclear species 1 was verified. Kinetic studies, in methanol solution, on the catalyzed TMPD oxidation indicated a first-order dependence of the initial rate with the catalyst concentration, and a saturation effect with increasing concentrations of the substrate. The dinuclear species was observed to be more reactive than the mononuclear one, and further experiments showed that the counter-ion chloride can significantly affect the kinetic parameters, mostly by shifting the mono-/dinuclear equilibrium, and stabilizing an ion-pair with the substrate.Keywords: copper(II) complexes, dinuclear species, equilibria, kinetics, catalytic activity IntroductionCopper complexes containing diimines have been extensively studied, and reported as good models for a variety of enzymes associated to the molecular oxygen metabolism. 1 Additionally some of them were used to construct exotic molecular architectures, sensitize photoelectrochemical cells, label biomaterials as the basis for selective sensors, and also to obtain new magnetic materials. 2 Copper-containing active sites are responsible, in vivo, for the catalyzed oxidation of phenols, and amines, where two-electron transfer occurs between the substrate and two metal centres, as in tyrosinase and catechol oxidases, 3 or 873 Equilibria and Catalytic Properties of a Chloro-Bridged Diimine Copper(II) Complex V...
The substitution of small amounts of Mn2+ by Cu2+ or Cd2+ ions in the linear chain antiferromagnet (CH3NH3)MnCl3⋅2H2O (TN=4.12 K) leads to the appearance of a remanent magnetic moment in the substituted compound. Magnetization measurements carried out in single crystals revealed that the remanent magnetization (Mr) appears along the direction of the easy axis when the sample is cooled through the ordering temperature in the presence of an axial magnetic field as low as few millioersteds. Samples with x∼0.01 of Cu and x=0.008 of Cd were investigated. The measured magnetization M=Mr+χ∥Haxial observed at applied axial fields Haxial=0.8 Oe in both crystals is almost entirely due to the contribution of Mr since χ∥Haxial is very small. Hysteresis curves were also obtained for the Cd diluted system and the results shows that at T=1.5 K a reversal in the direction of Mr is obtained for Haxial around 200 Oe. A comparison with previous recent observations in some three-dimensional diluted antiferromagnets is made.
The magnetization of the diluted and mixed low anisotropy antiferromagnets (K1−xRbx)2Fe1−yIny(Cl1−zBrz)5H2O was measured as a function of an applied magnetic field 0≤H≤4.0 T in the temperature range 1.5≤T≤15 K. The focus of this work is on the effects that random fields, generated by an external field applied along the easy axis, have on the spin-flop transition. The sharp first order transition that occurs in K2FeCl5H2O has its width increased by almost an order of magnitude when substitution is introduced in any of the K, Fe, or Cl sites. In K2Fe1−yInyCl5H2O and K2Fe(Cl1−zBrz)5H2O hysteseris is also observed. Hysteresis is not observed in (K1−xRbx)2FeCl5H2O.
The coupled spin-1 chains material NiCl2-4SC(NH2)2 (DTN) doped with Br impurities is expected to be a perfect candidate for observing many-body localization at high magnetic field: the so-called "Bose glass", a zero-temperature bosonic fluid, compressible, gapless, incoherent, and short-range correlated. Using nuclear magnetic resonance (NMR), we critically address the stability of the Bose glass in doped DTN, and find that it hosts a novel disorder-induced ordered state of matter, where many-body physics leads to an unexpected resurgence of quantum coherence emerging from localized impurity states. An experimental phase diagram of this new "order-from-disorder" phase, established from NMR T −1 1 relaxation rate data in the (13 ± 1)% Br-doped DTN, is found to be in excellent agreement with the theoretical prediction from large-scale quantum Monte Carlo simulations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.