Search

Here we report the synthesis, structure and detailed characterisation of three n-membered oxovanadium rings, Na$_n$[(V=O)$_n$Na$_n$(H$_2$O)$_n$($��$, $��$, or $��$-CD)$_2$]$m$H$_2$O (n = 6, 7, or 8), prepared by the reactions of (V=O)SO$_4$$\cdot$$x$H$_2$O with $��$, $��$, or $��$-cyclodextrins (CDs) and NaOH in water. Their alternating heterometallic vanadium/sodium cyclic core structures were sandwiched between two CD moieties such that O-Na-O groups separated neighbouring vanadyl ions. Antiferromagnetic interactions between the $S$ = 1/2 vanadyl ions led to $S$ = 0 ground states for the even-membered rings, but to two quasi-degenerate $S$ = 1/2 states for the spin-frustrated heptanuclear cluster., 8 pages, 8 figures, accepted for publication in Chemistry - A European Journal

A new procedure was developed in order to estimate the stress intensity factor for impact fracture toughness tests. The dynamic stress intensity factor is evaluated from the static stress intensity factor and the impact response function as a correction factor for inertia effect. The impact response function for arbitrary profile of dynamic load is computed by superposing the step response function for the specimen subjected to the step impact load. The step response function is evaluated from dynamic and static crack opening displacements, which can be calculated by finite element method. A numerical computation of the dynamic stress intensity factor was carried out for a problem of Thau and Lu. The accuracy of the present method was verified from the comparison of the numerical result with the analytical one. The impact fracture experiment conducted at Brown University was simulated to estimate the stress intensity factor in view of the dynamic fracture mechanics.

The preparation and physical characterization are reported for several single-molecule magnet salts to investigate the effects of paramagnetic cations on the magnetization relaxation behavior of [Mn12]- anionic single-molecule magnets., Comment: 30 pages, 5 tables, 15 figures

The first cobalt molecule to function as a single-molecule magnet, [Co4(hmp)4(MeOH)4Cl4], where hmp- is the anion of hydroxymethylpyridine, is reported. The core of the molecule consists of four Co(II) cations and four hmp- oxygen atoms ions at the corners of a cube. Variable-field and variable-temperature magnetization data have been analyzed to establish that the molecule has a S=6 ground state with considerable negative magnetoanisotropy. Single-ion zero-field interactions (DSz2) at each cobalt ion are the origin of the negative magnetoanisotropy. A single-crystal of the compound was studied by means of a micro-SQUID magnetometer in the range of 0.040-1.0K. Hysteresis was found in the magnetization versus magnetic field response of this single crystal. It is concluded that this is the first cobalt molecule to function as a single-molecule magnet., Comment: 10 pages, 4 figure, 2001 MMM conference