Antiferromagnetic rings

Entanglement in supramolecu-lar spin systems of two weakly coupled antiferromagnetic rings (Purple-Cr7Ni). Phys. Rev. Lett., 104, 037203. 

In Table 42, in complexes with SBs (97)-(99), the / values of compounds with n = 2 (n in R = (CH2) ) are larger than with n = 3. This suggests that the antiferromagnetic exchange interaction is stronger with n = 2, and this has been attributed to the difference in the chelate ring (five- or six-membered).775 For n-2, the J values also depend appreciably on the nature and position of the Hsal substituent for n - 3, they are relatively insensitive to ring substituents.358... 

The electronic structural change of radical-substituted diarylethenes accompanying the photoisomerization is the transformation between a disjoint non-Kekule structure and a closed-shell Kekule structure. One may infer from the above consideration that the interaction between spins in the open-ring isomer of diarylethene is weak, whereas significant antiferromagnetic interaction takes... 

Magnetic susceptibilities of 10a and 10b were measured on a SQUID suscep-tometer in microcrystalline form. %T-T plots are shown in Fig. 9.5. The data were analyzed in terms of a modified singlet-triplet two-spin model (the Blea-ney-Bowers-type), in which two spins (S = V2) couple antiferromagnetically within a biradical molecule by exchange interaction J. The best-fit parameters obtained by means of a least-squares method were 2J/kB = -2.2 + 0.04 K for 10a and -11.6 + 0.4 K for 10b. Although the interaction (2J/kB = -2.2 K) between the two spins in the open-ring isomer 10a was weak, the spins of 10b showed a remarkable antiferromagnetic interaction (2J/kB = -11.6 K). 

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