Beyond NICS: estimation of the magnetotropicityof inorganic unsaturated planar rings

A simple classical model of magnetic-field induced electron flow is used to evaluate the ring currentstrength for a few inorganic monocyclic compounds: B H N , B H O , P , N , Si H , N2��, Al2�� 33333366664 4and H6. It is shown that, for these neutral and charged systems, sustaining delocalized electroncurrents in the presence of a magnetic field Bext orthogonal to the sh plane, the out-of-planecomponent of the nuclear magnetic shielding along the central axis is connected to the out-of-planemagnetizability by a simple equation, involving the radius of an average loop of current. A novelestimate of this effective radius is provided. Reliable ring current susceptibilities (that is, currentstrengths) can be evaluated by a simple relationship, using the out-of-plane components of nuclearshielding and magnetizability tensors. The accuracy of the current susceptibilities calculated by theclassical model is established by comparison with corresponding ab initio estimates obtained byintegrating the quantum mechanical current-density vector field. The out-of-plane components ofnuclear shielding and magnetizability are both strongly biased by the molecular geometry. Theircombined use to estimate the ring current susceptibility offers a quantifier of magnetotropicitymore reliable than (i) the x out-of-plane component of magnetizability, (ii) the sCM out-of-plane JJcomponent of the magnetic shielding at the center of mass, widely reported as NICS (0) = ��sCM. JJThe inadequacy of these commonly adopted magnetotropicity measures is demonstrated by comparing a set of related molecules, C6H6 and Si6H6, N6 and P6.