High spin molecules

A more pronounced enhancement of the paramagnetism is obtained when several Fe(III) or Mn(II) centres, each bringing s = 5/2, are assembled in a 

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Weltner et al. have performed an ESR and optical study of the high spin molecules MnH and MnHa (and possibly MnHa) in Ar and Ne at 4K. 

Generation and characterization of high-spin organic molecules 210 Cross-conjugated poly(carbenes) 210 Other high-spin molecules 215... 

In this review, we focus our discussion on organic molecules with more than two coupled spins (S > 3/2). They are arbitrarily called high-spin molecules (Itoh, 1978 Weltner, 1983). Molecular solids in which more than two unpaired electrons are aligned in parallel among neighbouring molecules will also be discussed. 

There are several independent measurements available for confirming that high-spin molecules are really obtained. 

As suggested earlier, high-spin molecules that have thousands of parallel spins would correspond to single domain particles of ferromagnetic substances. In a-iron, for example, a microcrystalline particle of radius 200 pm contains ca. 5000 spins and is considered to form a single domain structure. 

Design of ferromagnetic coupling among organic free radicals and high-spin molecules in molecular assemblies... 

Anyway, high-spin molecules of low dimensionality cannot become ferro-magnets by themselves. The additional stability at finite temperature should be derived from intermolecular interaction. Therefore the interplay of the two factors appears to be most desirable. 

In comparison with hydrocarbons, aromatic amines easily transform into cation radicals. Structures of these cation radicals are well documented on the basis of their ESR spectra and MO calculations (see, e.g., Grampp et al. 2005). The stable cation radical of A/,A,A, A -tetramethyl-p-phenylenediamine (the so-called Wuerster s blue) was one of the first ion radicals that was studied by ESR spectroscopy (Weissmann et al. 1953). The use of this cation radical as a spin-containing unit for high-spin molecules has been reported (Ito et al. 1999). Chemical oxidation of N,N -bis [4-(dimethylamino)-phenyl-A/,A -dimethyl-l,3-phenylenediamine with thianthrenium perchlorate in -butyronitrile in the presence of trifluoroacetic acid at 78°C led to the formation of the dication diradical depicted in Scheme 3.58. 

Fractal Character of Dendritic High-Spin Molecules.40... 

Figure 13. Dependence of AA H° on AAS° for the different isomers of the dendritic high-spin molecule 6 (G = 1) in the studied chromatographic system.

High-spin dendrimers, like 5 (G = 1), are ideal probes for such a study since they are ESR active and this spectroscopy has the same time scale as such a dynamic process. In fact, the anisotropic components of some ESR parameters, such as those responsible for the fine structures of a high-spin molecule, are averaged out under molecular tumbling leading to noticeably lineshape effects. 

J. A. Berson, in The Chemistry of the Quinonoid Compounds, Vol. II, Eds., S. Patai and Z. Rappoport), John Wiley Sons, Inc., New York, 1988. Chapter 10. This article gives a list of reviews on the EPR spectroscopy of high-spin molecules. 

Fig. 2a-c. Schematic representation of various types of spin crossover behaviour, x s (T) is the fraction of high spin molecules as a function of temperature, a Gradual and abrupt spin transition, respectively b incomplete spin transition (RP is the residual fraction of high spin molecules) c spin transition with hysteresis, and Tj are the transition temperatures in the cooling and heating mode, respectively... 

Consequences of the Fractal Character of Dendritic High-Spin Molecules on Some of their Physicochemical Properties [N. Ventosa, D. Ruiz, C. Rovira, J. Veciana, Chapt. 5],... 

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