Lanthanide ions radicals

It is interesting to stress that the spin chirality observed in the gadolinium radical chains differs from the more usual one that characterizes anisotropic materials and is solely due to the significant strength of NNN interactions between lanthanide ions that are very far apart. The mechanism responsible for this interaction remains unclear and the complexity of the system has, up to now, hampered an ab initio investigation of the phenomenon. 

In this sub-chapter, selected examples of lanthanide-based chains are described. We have chosen to comment on only systems with structural characterization and significant dynamic properties. Chains with a sole lanthanide ion as spin carrier are described first. 3d-4f and 3d-3d -4f heterometallic chains follow. Finally, chains comprising lanthanide and radical ligands conclude this chapter. 

The other important classes of molecules/ions containing more than one unpaired electron are transition-metal and lanthanide ion-complexes. In general (although not always) these do not exhibit the reactions of Scheme 1.1 and hence are not usually classed as radicals. Often they are very stable, examples being high-spin Mn(II) and Ni(II) the major reaction linking them with radicals is that of electron transfer. (Transition-metal complexes can have up to 5(d) unpaired... 

The luminescence transitions show an intriguing phenomenological dependence on the number of radical ligands, the ancillary ligands and the coordination number of the lanthanide ion. Figure 8a,b compare the highest... 

The lack of free electrons endows basic ceramics with poor thermal and electronic conductivity. The chemical flexibihty of ceramics, however, allows them to be selectively doped with other ions. In particular, doping with transition metal or lanthanide ions generates a wide variety of colours and can radically alter electronic and magnetic properties. Thus, insulators can be transformed into superconductors. How this comes about is described in Part 4, Chapters 10-15. 

If the point symmetry group of the lanthanide ion does not possess an inversion, the magnetization linear in an external electric field may be observed, and the dielectric susceptibility of the sample may be also radically affected by an external or internal magnetic field. Electric field effects on the EPR spectra of the lanthanide ions in insulators are well known (see, for example, Sakharov 1979, 1980), and here we shall consider only the alteration of the dielectric properties of the crystal due to the ordering in the lanthanide subsystem. Dielectric measurements are often used to plot the phase boundaries of the lanthanide magnets in the magnetic field. The eneigy of the lanthanide ion in the quasistatic electric field is presented in eq. (9). The effective even dipole moment of the ion can be written as follows... 

The subsequent debate entertained further applications and potential studies. Specifically, introduction of radical anions into the lariat could produce molecules suitable for electrochemical transport. An extension to the complexation of lanthanide ions echoed the concept alluded to by Jean-Marie Lehn the previous evening. 

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