Dipartimento di Chimica dell'Universitá degli Studi di Modena e Reggio Emilia, via Campi 183, 41100 Modena, Italy.
Phys Chem Chem Phys. 2011 Dec 14;13(46):20666-72. doi: 10.1039/c1cp21952a. Epub 2011 Oct 12.
A simple classical model of magnetic-field induced electron flow is used to evaluate the ring current strength for a few inorganic monocyclic compounds: B(3)H(3)N(3), B(3)H(3)O(3), P(6), N(6), Si(6)H(6), N, Al and H(6). It is shown that, for these neutral and charged systems, sustaining delocalized electron currents in the presence of a magnetic field B(ext) orthogonal to the σ(h) plane, the out-of-plane component of the nuclear magnetic shielding along the central axis is connected to the out-of-plane magnetizability by a simple equation, involving the radius of an average loop of current. A novel estimate of this effective radius is provided. Reliable ring current susceptibilities (that is, current strengths) can be evaluated by a simple relationship, using the out-of-plane components of nuclear shielding and magnetizability tensors. The accuracy of the current susceptibilities calculated by the classical model is established by comparison with corresponding ab initio estimates obtained by integrating the quantum mechanical current-density vector field. The out-of-plane components of nuclear shielding and magnetizability are both strongly biased by the molecular geometry. Their combined use to estimate the ring current susceptibility offers a quantifier of magnetotropicity more reliable than (i) the ξ(∥) out-of-plane component of magnetizability, (ii) the σ(∥)(CM) out-of-plane component of the magnetic shielding at the center of mass, widely reported as NICS(∥)(0) = -σ(∥)(CM). The inadequacy of these commonly adopted magnetotropicity measures is demonstrated by comparing a set of related molecules, C(6)H(6) and Si(6)H(6), N(6) and P(6).
B(3)H(3)N(3)、B(3)H(3)O(3)、P(6)、N(6)、Si(6)H(6)、N、Al 和 H(6)。结果表明，对于这些中性和带电体系，在垂直于σ(h)平面的磁场 B(ext)存在的情况下维持非定域电子电流，沿中心轴的核外屏蔽的外场分量与磁各向异性由一个简单的方程连接，涉及电流的平均环半径。提供了这种有效半径的新估计。通过使用核屏蔽和磁各向异性张量的外场分量，可以通过简单的关系可靠地评估环电流磁化率（即电流强度）。通过将量子力学电流密度矢量场积分，与相应的从头算估计值进行比较，确立了经典模型计算的电流磁化率的准确性。核屏蔽和磁各向异性的外场分量都强烈受到分子几何形状的影响。它们的结合使用可提供比（i）磁各向异性的ξ(∥)外场分量、（ii）质心处磁屏蔽的σ(∥)(CM)外场分量更可靠的环电流磁化率的量度，后者广泛报道为 NICS(∥)(0) = -σ(∥)(CM)。通过比较一组相关分子 C(6)H(6)和 Si(6)H(6)、N(6)和 P(6)，证明了这些常用的磁各向异性量度的不充分性。
