On the validity of the McConnell-I model of ferromagnetic interactions: The [2.2]paracyclophane example
On the validity of the McConnell-I model of ferromagnetic interactions: The [2.2]paracyclophane example
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DOI：
10.1021/jp982252g
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发表时间：
1998-10-22
影响因子：
2.9
通讯作者：
Robb, MA
中科院分区：
文献类型：
--
作者：
Deumal, M;Novoa, JJ;Robb, MA
在VB空间中严格实现的海森堡哈密顿模型与McConnell-I模型之间的正式比较表明，McConnell模型的有效性依赖于后者中的自旋密度乘积与前者中的自旋交换密度矩阵元素之间的启发式一一对应。使用严格的海森堡汉密尔顿，对伪邻位、伪角位、伪角位的单重态/五重态稳定性进行了数值模型计算。和pseudopara bis（苯亚甲基）[2.2]对环芳（用相应的单重态/三重态双（甲基）[2.2]对环芳模拟）表明，McConnell模型对低和高自旋稳定性的正确预测仅仅是因为来自“最紧密接触”的贡献。不直接排列的碳原子相当小。在对准不完美的系统中，这种抵消可能不成立。在VB海森堡哈密顿量的自旋交换密度矩阵元素的差异，在麦康奈尔模型中的自旋密度产品之间的关联是有效的，因为麦康奈尔模型正确地预测在VB扩展的领先配置项。
A formal comparison between a rigorous implementation of a Heisenberg Hamiltonian model in a VB space with the McConnell-I model shows that the validity of the McConnell model rests upon a heuristic one-to-one correspondence between spin density products in the latter with the difference of the spin exchange density matrix elements in the former. Using a rigorous Heisenberg Hamiltonian, a numerical model computation of the singlet/quintet stability for pseudo ortho, pseudometa, and pseudopara bis(phenylmethylenyl)[2.2]paracyclophanes (modeled with the correponding singlet/triplet bis(methyl)[2.2]paracyclophanes) shows that the McConnell model makes the correct prediction of low and high spin stability only because the contributions from "closest contact" carbon atoms that are not directly aligned is rather small. In systems where the alignment is not perfect, this cancelation may not hold. The association between spin density products in the McConnell model with the difference of the spin exchange density matrix elements in the VB Heisenberg Hamiltonian is shown to be valid because the McConnell model correctly predicts the leading configuration terms in the VB expansion.