RESUMO
The synthesis, structural, and magnetic characterization of [FeIII4LnIII4(teaH)8(N3)8(H2O)] (Ln = Gd and Y) and the previously reported isostructural Dy analogue are discussed. The commonly held belief that both FeIII and GdIII can be regarded as isotropic ions is shown to be an oversimplification. This conclusion is derived from the magnetic data for the YIII analogue in terms of the zero-field splitting seen for FeIII and from the fact that the magnetic data for the new GdIII analogue can only be fit employing an additional anisotropy term for the GdIII ions. Furthermore, the Fe4Gd4 ring shows slow relaxation of magnetization. Our analysis of the experimental magnetic data employs both density functional theory as well as the finite-temperature Lanczos method which finally enables us to provide an almost perfect fit of magnetocaloric properties.
RESUMO
The synthesis and characterization of size-separated silicon nanocrystals functionalized with a heteroatom-substituted organic capping group, allylphenylsulfide, via photochemical hydrosilylation are described for the first time. These silicon nanocrystals form colloidally stable and highly photoluminescent dispersions in non-polar organic solvents with an absolute quantum yield as high as 52% which is 20% above that of the allylbenzene analogue. Solutions of the size-separated fractions are characterized over time to monitor the effect of aging in air by following the change of their photoluminescence and absolute quantum yields, supplemented by transmission electron microscopy.