Global Journalist: Investigators dig into the bombing of an Israeli hotel in Mombasa; Saddam Hussein claims no weapons of mass destruction

In this December 5, 2002 episode of Global Journalist, host Stuart Loory interviews three journalists about two different news items of the day -- the bombing of an Israeli-owned hotel in Mombasa, Kenya, and the claims by Saddam Hussein that Iraq has no weapons of mass destruction

Slow Magnetic Relaxation in a High-spin Iron(II) Complex

(Graph Presented) Slow magnetic relaxation is observed for [(tpa Mes)Fe] -, a trigonal pyramidal complex of high-spin iron(II), providing the first example of a mononuclear transition metal complex that behaves as a single-molecule magnet. Dc magnetic susceptibility and magnetization measurements reveal a strong uniaxial magnetic anisotropy (D = -39.6 cm -1) acting on the S = 2 ground state of the molecule. Ac magnetic susceptibility measurements indicate the absence of slow relaxation under zero applied dc field as a result of quantum tunneling of the magnetization. Application of a 1500 Oe dc field initiates slow magnetic relaxation, which follows a thermally activated tunneling mechanism at high temperature to give an effective spin-reversal barrier of U eff = 42 cm -1 and follows a temperature-independent tunneling mechanism at low temperature. In addition, the magnetic relaxation time shows a pronounced dc-field dependence, with a maximum occurring at ∼1500 Oe. Copyright © 2010 American Chemical Society

Slow Magnetic Relaxation in a Family of Trigonal Pyramidal Iron(II) Pyrrolide Complexes

We present a family of trigonal pyramidal iron(II) complexes supported by tris(pyrrolyl-α-methyl)amine ligands of the general formula [M(solv) n][(tpaR)Fe] (M = Na, R = tert-butyl (1), phenyl (4); M = K, R = mesityl (2), 2,4,6-triisopropylphenyl (3), 2,6-difluorophenyl (5)) and their characterization by X-ray crystallography, Mössbauer spectroscopy, and high-field EPR spectroscopy. Expanding on the discovery of slow magnetic relaxation in the recently reported mesityl derivative 2, this homologous series of high-spin iron(II) complexes enables an initial probe of how the ligand field influences the static and dynamic magnetic behavior. Magnetization experiments reveal large, uniaxial zero-field splitting parameters of D = -48, -44, -30, -26, and -6.2 cm-1 for 1-5, respectively, demonstrating that the strength of axial magnetic anisotropy scales with increasing ligand field strength at the iron(II) center. In the case of 2,6-difluorophenyl substituted 5, high-field EPR experiments provide an independent determination of the zero-field splitting parameter (D = -4.397(9) cm-1) that is in reasonable agreement with that obtained from fits to magnetization data. Ac magnetic susceptibility measurements indicate field-dependent, thermally activated spin reversal barriers in complexes 1, 2, and 4 of Ueff = 65, 42, and 25 cm-1, respectively, with the barrier of 1 constituting the highest relaxation barrier yet observed for a mononuclear transition metal complex. In addition, in the case of 1, the large range of temperatures in which slow relaxation is observed has enabled us to fit the entire Arrhenius curve simultaneously to three distinct relaxation processes. Finally, zero-field Mössbauer spectra collected for 1 and 4 also reveal the presence of slow magnetic relaxation, with two independent relaxation barriers in 4 corresponding to the barrier obtained from ac susceptibility data and to the 3D energy gap between the MS = ±2 and ±1 levels, respectively

Magnetic Bistability in Mononuclear Iron(II) Pyrrolide Complexes and Cyano-bridged Chain Compounds

This presentation will describe our efforts to engender high magnetic relaxation barriers in low-dimensional coordination compounds. First, strong magnetic anisotropy in a family of iron(II) pyrrolide complexes is shown to give rise to the first examples of transition metal-based mononuclear single-molecule magnets. The anisotropy and relaxation dynamics of these complexes are examined through an array of magnetic and spectroscopic measurements. Next, a building block approach is employed to install strong coupling in cyano-bridged chain compounds. In particular, simple molecular orbital considerations are used to design and construct the compound (Bu4N)[TpCuReCl4(CN)2], which demonstrates the strongest ferromagnetic coupling ever observed through cyanide. Finally, this approach is extended toward the assembly of a series of single-chain magnets, (DMF)4MReCl4(CN)2 (M = Mn, Fe, Co, Ni). Most notably here, the field-dependent magnetization of the iron analogue exhibits significant hysteresis at low temperature, thus demonstrating classical magnet behavior in a one-dimensional solid