Six-coordinate Co(2+) with H(2)O and NH(3) ligands: which spin state is more stable?

Octahedral, six-coordinate Co(2+) can exist in two spin states. For biological ligands, H(2)O and NH(3), the most stable spin state is high spin (S = (3)/(2)). The difference in energy between high and low spin is dependent upon the ligand mix and coordination stereochemistry. High spin optimized geometries for these model compounds give structures close to octahedral symmetry. Low spin permits significant Jahn-Teller distortion. H(2)O ligands preferentially assume axial positions. Continuum solvent has a greater effect on low spin Co(2+), and it reduces the energy difference between the two spin states. For some ligand combinations optimized in the presence of solvent, there is no significant difference in energy between spin states.     

Biological nanophase magnetic materials

Biological systems provide a number of examples of magnetic materials in which key structural features are in the nanometre size range. These can be used as model systems for investigations of their magnetic behaviour or they can provide a source of novel magnetic materials. Both of these aspects will be considered in this review, with particular reference to the use of Mössbauer spectroscopy as a technique for both characterisation and magnetic investigation.     

Quasirotational groundstate bands of even-even nuclei with 50≦N,Z≦82

The quasirotational groundstate bands of¹⁴⁰Sm,¹⁴²Sm,¹⁴⁴Gd and¹³⁶Nd have been determined by studying the prompt γ-decay after (α,xn+yp+zα.) reactions using α-particles of up to 104 MeV and targets of¹⁴⁴Sm,¹⁴²Nd,¹⁴¹Pr,¹⁴⁰Ce,¹³⁶Ce and¹³⁹La. The new levels continue the trends of the neighbouring even-even nuclides smoothly. These systematics of the groundstate bands in the region 50<N,Z<82 are not disturbed by expected subshell closure effects.     

Relativmessung der Elektronenpolarisation beimβ-Zerfall: Tl204 und P32

The ratio of longitudinal polarization values of Tl²⁰⁴ and P³² β-particles was measured by the method of double scattering. The result obtained is P(Tl²⁰⁴)/P(P³²)=0.993±0.036 at 540 keV. The low specific activity of the available Tl²⁰⁴ sources caused a considerable depolarization ofβ-particles by scattering in the source. The influence of depolarization was eliminated by using sources containing both nuclei in a chemical compound. The ratio of polarization values can then be calculated from the time dependence of the scattering asymmetry, as the half-lives of Tl²⁰⁴ and P³² differ considerably. An estimate is presented of the influence of inelastic scattering processes in the source on electron depolarization.     

Relativmessung der Elektronenpolarisation beim β-Zerfall: Au199 und P32

The ratio of longitudinal polarization values of Au¹⁹⁹ and P³² particles was measured by the method of double scattering. The result obtained isP(Au¹⁹⁹)/P(P³²)=0.83±0.05 at 310 keV for the ground state transition of Au¹⁹⁹.