Rajca

Rajca, A. Wongsriratanakul, J. Rajca, S. Cemy, R. A Dendritic Macrocyclic Organic Polyradical With a Very High Spin of S = 10. Angew. Chem., Int. Ed. 1998, 37, 1229-1232. 

The distance between the two spin-bearing centers is mnch greater in the structure shown in Scheme 1.39 than that shown in Scheme 1.38. Note that in this case, a control of spin coupling via control of electron localization is attained. The straightforward control of electron localization was implemented via modification of the snbstitnents at the center site (compare Schemes 1.38 and 1.39). The mentioned anion-diradicals were prepared by partial oxidation of relative polyanions with iodine (Rajca and Rajca 1995). When the carbanion-stabilized 4-biphenyl, in the place of 4-tert-butylphenyl, was employed as a snbstitnent at the center site, the negative charge was confined to the center site and the spin density to the terminal (nonadjacent) site. 

The large overcrowding present in the dendrimer series 5 and 6, as well as in the dendritic polymer 4 obtained by Rajca et al., show that the use of dendritic architectures to produce super high-spin macromolecules has some practical weak-... 

Rajca and co-workers have studied star-branched and dendritic high-spin polyradicals which are potential organic magnets. Representative data were obtained for the model tetra-anionic compound 55. Three redox waves were observed by cyclic voltammetry and differential pulse voltammetry for a four-electron process between the potentials of -2.00 and -1.20 V (vs. SCE). Electrochemical experiments with these materials have usually been performed at 200 K. The polyradicals, which are less stable for systems with more unpaired electrons, have been characterized by spectroscopic studies, ESR data, and SQUID magnetometiy. 

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