THE 1ST ISOLATED CARBON TETRARADICAL WITH A PAIR OF TRIPLETS

被引:24
作者
CARILLA, J
JULIA, L
RIERA, J
BRILLAS, E
GARRIDO, JA
LABARTA, A
ALCALA, R
机构
[1] UNIV BARCELONA,DEPT QUIM FIS,E-08028 BARCELONA,SPAIN
[2] UNIV BARCELONA,DEPT FIS FUNDAMENTAL,E-08028 BARCELONA,SPAIN
[3] UNIV ZARAGOZA,CSIC,INST CIENCIAS MAT ARAGON,E-50009 ZARAGOZA,SPAIN
关键词
D O I
10.1021/ja00022a013
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
The synthesis of trans-perchlorovinylenebis(alpha,alpha,alpha',alpha'-tetraphenyl-,3-xylylene) (1), an exceptionally stable organic carbon tetraradical, which is isolated as a deep red solid, stable in air up to 200-degrees-C, is reported. The electronic spectrum of 1 is presented and commented on. The cyclic voltammogram of 1, exhibiting two consecutive redox couples with standard potentials of -0.175 and-0.480 V vs SCE, is discussed in view of the exhaustive controlled-potential electrolysis of the tetraradical into the corresponding tetraanion. Magnetic susceptibility measurements from 4.2 to 300 K show that a pair of triplets is the ground state of the tetraradical, being 2J = 240 +/- 10 cm-1 (0.69 kcal/mol), the triplet-singlet energy gap. At low temperatures, a weak antiferromagnetic interaction was observed (negative and low value of Weiss constant THETA = 1.1 +/- 0.1 K). From an EPR analysis in frozen 2-methyltetrahydrofuran over the range 4-129 K, the presence of two diastereoisomeric forms of the molecule is tentatively suggested. Accordingly, from the two symmetric and outer pairs of peaks of DELTA-m(s) = +/- 1 transition in the spectrum, two different \D/hc\ values, 0.010 and 0.013 cm-1, are calculated that are in good agreement with those reported for perchloro-m-xylylene. Supporting the presence of the two forms of 1, the DELTA-m(s) = +/- 2 transition exhibits two overlapping lines. The intensity of this transition rises continuously from 129 to 4 K, also supporting that the ground state is a pair of triplets.
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收藏
页码:8281 / 8284
页数:4
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