Units magnetic parameters

Table 13 Structural and magnetic parameters for dimers with the [Ni(/r-l,3-N3)Ni] unit Ni—N bond distances (A), Ni—N—N and r angles (°), J incm 1.a...

We have described above the evolution of the magnetic properties of the [Cp2M (dmit)]AsFg salts upon isomorphous Mo/W substitution. Another possibility offered by this attractive series is the isomorphous substitution of the counter ion, that is PFg- vs AsF6 vs Sbl- fi. Electrocrystallization experiments conducted with [Cp2Mo(dmit)] and the three different electrolytes afforded an isomorphous series, with a smooth evolution of the unit cell parameters with the anion size [32], This cell expansion with the anion size leads to decreased intermolecular interactions between the [Cp2Mo(dmit)]+ radical cation, as clearly seen in Table 2 from the decreased Curie-Weiss temperatures and Neel temperatures (associated with the transition they all exhibit to an AF ground state). 

The magnetic properties of deoxyHr indicate that a bridge between the iron centers persists but may be altered from that in oxyHr. The NMR spectrum of deoxyHr exhibits large isotropic shifts for the N-H s on histidines coordinated to the binuclear unit. Mossbauer parameters of deoxyHr (Table II) are typical of high spin iron(II) centers which are at best weakly coupled (37,38,39). Room temperature magnetic susceptibility measurements using the Evans NMR technique... 

X-ray diffraction investigation (Co-Ka radiation) was made on the powder samples for the phase identification both the parent compound and its hydride and to determine the unit cell parameters. The magnetisation measurements were carried out with a SQUID (Quantum Design MPMS 5-S) magnetometer from 5 to 340 K in magnetic fields up to 50 kOe. 

The Rietveld refinements of the low temperature data, 250 - 5 K, converged successfully with use of the room-temperature, I2/m structural model. Table 1. The occupations of the oxygen and Cr/Nb cation sites were fixed at the values obtained from the room-temperature refinement. When occupancy refinement was attempted with the neutron data their least squares shifts were hi ly correlated with those of the thermal parameters. The thermal parameters for all the atoms decreased smoothly with decreasing temperature. Magnetic reflections or magnetic intensity added to existing reflections were not observed at any temperature. Unit cell parameters, atomic positions, occupational and thermal parameters, bond distances and bond angles as a function of temperature are listed in Table 1. 

The hydroxides of berklium(III), Bk(OH)3, and califomium(III), Cf(OH)s, behave in a similar fashion [3]. In their crystalline forms, Am(OH)s and Cm(OH)3 are anhydrous (as are hydroxides of light rare-earth elements), and are hexagonal, C 6h P s/m space group, a = 6.420 and 6.391 A, c = 3.745 and 3.712 A, for Am and Cm compounds, respectively. Due to self-irradiation, the unit-cell parameters increase with time, as does the sample amorphization. In the case of " Cm(OH)3, the stmcture decomposes within 1 day, but the same process for " Am(OH)3 takes up to 4-6 months [4]. The Mossbauer spectrum of Am(OH)3 [5] is characterized by 5 = 4.6 cm/c (relative to Am02). The nuclear magnetic resonance (NMR) studies indicate that, among the TUE(III) hydroxides, the Am compound has the most covalent chemical bonds. The TUE(III) hydroxides are readily soluble in different mineral acids under these conditions, the solutions of hydrated An ions are produced. 

The site occupation is such that of the four sites in fig. 1, A and C are identically occupied, as are B and D. The structure may therefore be viewed on a smaller unit cell with a lattice parameter one half of the equivalent L2j cell. Table 33 lists the magnetic parameters of these alloys. 

The derivatives are evaluated at the point B = p,M = p,N = fle = 0. These reduced magnetic parameters may require a transformation when compared with experimental data (unit homogeneity). Note that 1c is a symmetric tensor whereas aN is not. 

Iron has a saturation magnetisation of 1.72xlO Am What is the measured magnetic moment, in Bohr magnetons, of an iron atom. Iron has an A2 structure, with a cubic unit cell parameter of 0.2867 nm. 

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