Hydroquinone-bridged dinuclear CuII complexes and single-crystalline CuII coordination polymers

Evidence of a field-induced Berezinskii-Kosterlitz-Thouless scenario in a two-dimensional spin-dimer system

Two-dimensional (2D) systems with continuous symmetry lack conventional long-range order because of thermal fluctuations. Instead, as pointed out by Berezinskii, Kosterlitz and Thouless (BKT), 2D systems may exhibit so-called topological order driven by the binding of vortex-antivortex pairs. Signatures of the BKT mechanism have been observed in thin films, specially designed heterostructures, layered magnets and trapped atomic gases. Here we report on an alternative approach for studying BKT physics by using a chemically constructed multilayer magnet. The novelty of this approach is to use molecular-based pairs of spin S=½ ions, which, by the application of a magnetic field, provide a gas of magnetic excitations. On the basis of measurements of the magnetic susceptibility and specific heat on a so-designed material, combined with density functional theory and quantum Monte Carlo calculations, we conclude that these excitations have a distinct 2D character, consistent with a BKT scenario, implying the emergence of vortices and antivortices.

Vanadium(IV/V)-p-dioxolene temperature induced electron transfer associated with ligation/deligation of solvent molecules

Reaction of an aqueous solution of NaVO3 or a methanol solution of [VO(acac)2] with 2,5-bis((bis(2-hydroxyethyl)amino)methyl)hydroquinone, H6bdeah, results in the formation of two major vanadium species characterized by X-ray crystallography: the [(V(5+)O)2(bdeah)] and the [(V(4.5+)O)2(bdeas)S2] (S = DMSO or MeOH). The vanadium ions in the two species have a trigonal pyramidal and an octahedral coordination sphere respectively. Variable temperature UV-Vis and (51)V NMR spectroscopy as well as EPR and electrochemistry showed a temperature induced electron transfer. The diamagnetic [(V(5+)O)2(bdeah)] is the main species at high temperature. At low temperature one electron is transferred from the bdeah(6-) to the two vanadium centers resulting in the [(V(4.5+)O)2(bdeas)S2] species [H5bdeas = 2,5-bis((bis(2-hydroxyethyl)amino)methyl)-1,4-semiquinone]. The thermodynamic parameters of this intramolecular electron transfer were calculated by UV-Vis (ΔH = -36 ± 2 kJ mol(-1) and ΔS = -129 ± 5 J mol(-1) K(-1)) and (51)V NMR spectroscopy (ΔH = -37 ± 2 kJ mol(-1) and ΔS = -109 ± 5 J mol(-1) K(-1)). The electron transfer is a result of the large change of entropy which is associated with the ligation of the solvent molecules and the geometry change. EPR spectroscopy shows that most of the electron density in [(V(4.5+)O)2(bdeas)S2] is mainly located on the two vanadium ions.

(Acetonitrile-κN)chloridobis[2-(pyridin-2-yl)phenyl-κC,N]iridium(III)

The Ir(III) atom of the title compound, [Ir(C(11)H(8)N)(2)Cl(CH(3)CN)], displays a distorted octa-hedral coordination. The pyridyl groups are in trans positions [N-Ir-N = 173.07 (10)°], while the phenyl groups are trans with respect to the acetonitrile and chloride groups [C-Ir-N = 178.13 (11) and C-Ir-Cl = 176.22 (9)°]. The pyridyl-phenyl groups only show a small deviation from planarity, with the dihedral angle between the planes of the two six-membered rings in each pyridyl-phenyl group being 5.6 (2) and 5.8 (1)°. The crystal packing shows inter-molecular C-H⋯Cl, C-H⋯π(acetonitrile) and C-H⋯π(pyridyl-phen-yl) contacts.