X-ray Crystallography and Magnetic Studies of a Stable Macrocyclic Tetranitroxide. Intramolecular Dimer of Nitroxides in a Constrained Geometry of the Upper Rim of Calix[4]arene
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- 作者：Andrzej Rajca ; Maren Pink ; Teerapat Rojsajjakul ; Kan Lu ; Hua Wang ; and Suchada Rajca
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：July 16, 2003
- 年：2003
- 卷：125
- 期：28
- 页码：8534 - 8538
- 全文大小：226K
- 年卷期：v.125,no.28(July 16, 2003)
- ISSN：1520-5126
文摘
Synthesis, crystallography, and magnetic characterization of a stable macrocyclic tetranitroxide1, a calix[4]arene, which is functionalized with four tert-butylnitroxides at the upper rim, is described. Insolution, 1 has a 4-fold symmetric fixed cone conformation on the NMR time scale and small, butnonnegligible, exchange interactions between the radicals (30 K > 
J/k 
1.8 mK). In the solid state,dimerization of one diagonal pair of nitroxides leads to a pinched cone conformation for 1 with strongintradimer antiferromagnetic coupling with J/k = 200-300 K (singlet-triplet energy gap, 
EST 
1 kcal/mol).
J/k 1.8 mK). In the solid state,dimerization of one diagonal pair of nitroxides leads to a pinched cone conformation for 1 with strongintradimer antiferromagnetic coupling with J/k = 200-300 K (singlet-triplet energy gap, EST 1 kcal/mol).