Effects of Spin-Orbit Coupling on Covalent Bonding and the Jahn-Teller Effect Are Revealed with the Natural Language of Spinors

The orbital-based natural language describing the complexity of chemistry (Stowasser, R; Hoffmann, R. J.. Am. Chem. Soc. 1999, 121, 3414) was extended by us recently to the definition of spin-orbit natural spinors (Zeng, T. et al. J. Chem. Phys. 2011, 134, 214107). This novel method gives chemical insights into the role of spin-orbit coupling in covalent bonding and in the Jahn-Teller effect. The natural spinors are used to explain antibonding spin-orbit effects on TlH and Tl-2: it is found that the spin orbit induced charge transfer from the bonding to the nonbonding or antibonding orbitals has a large effect on the bond strength. The natural spinors are also used to explain the spin-orbit quenching of the Jahn-Teller effect in WF5: the spin-orbit interaction can stabilize the totally symmetric electron distribution so that the high symmetry molecular structure becomes more stable than its distortions. A general discussion of the role of the spin orbit coupling in covalent bonding and Jahn-Teller effect is given in terms of the competition between the rotational nature of the spin-orbit coupling and the directionality of the two effects. The natural spinors offer the advantage of providing a simple and clear pictorial explanation for the profound relativistic spin-dependent interactions in chemistry often appearing as a black box answer.