Magnetic properties and crystal structures of 1,5-diphenylverdazyls with electron acceptor groups in the 3-position
Magnetic properties and crystal structures of 1,5-diphenylverdazyls with electron acceptor groups in the 3-position
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DOI：
10.1021/jp972195b
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发表时间：
1997-11-13
影响因子：
3.3
通讯作者：
Neugebauer, FA
中科院分区：
文献类型：
--
作者：
Mito, M;Takeda, K;Neugebauer, FA
通过测量磁化率和热容，研究了电子受体基团为3位的4个二苯基- 2-5的磁性能。确定了3和4的晶体结构，对2的晶体结构进行了分析，改进了精密度。Verdazyl 2为反铁磁体，Neel温度为T-N = 1.16 +/- 0.04 K。在转变温度T-N以上，2表现为准一维海森堡铁磁体，链内交换相互作用为2J/k(B) = +7.0 +/- 1.0 k。链间交换相互作用zJ′/k(B)估计为-1.5 +/- 0.2 k，其中z为每个自旋的链间键数。另一方面，3和5表现为一维非交变和交变Heisenberg反铁磁体，交换相互作用分别为2J/k(B) = -11.6 k和2J(1)/k(B) = -113 k(交替参数α = J（2)/J(1) = 0.4）。4的磁化率符合居里-魏斯定律，在100 K以上，负的魏斯常数为-18 K。在100k以下，4表现出异常的磁性行为，不能用一个简单的模型来解释。根据晶体结构分析的结果，讨论了2-4的磁性能。
The magnetic properties of four diphenylverdazyls (2-5) with electron acceptor groups in the 3-position were studied by measuring the magnetic susceptibility and heat capacity. The crystal structures of 3 and 4 were determined, and for 2 the crystal structure analysis led to an improved refinement. Verdazyl 2 was found to be an antiferromagnet with a Neel temperature of T-N = 1.16 +/- 0.04 K. Above the transition temperature T-N, 2 behaves as a quasi-one-dimensional Heisenberg ferromagnet with the intrachain exchange interaction of 2J/k(B) = +7.0 +/- 1.0 K. The interchain exchange interaction zJ'/k(B) was estimated to be -1.5 +/- 0.2 K, where z is the number of interchain bonds per spin. On the other hand, 3 and 5 behave as 1D nonalternating and alternating Heisenberg antiferromagnets with an exchange interaction of 2J/k(B) = -11.6 K and 2J(1)/k(B) = -113 K (alternation parameter alpha = J(2)/J(1) = 0.4), respectively. The susceptibility of 4 follows the Curie-Weiss law with a negative Weiss constant of -18 K above 100 K. Below 100 K, 4 showed anomalous magnetic behavior that cannot be explained by a simple model. The magnetic properties of 2-4 are discussed based on the results obtained by crystal structure analyses.