Unusual long-range spin-spin coupling in fluorinated polyenes: A mechanistic analysis

Gräfenstein, Jürgen; Cremer, Dieter
November 2007
Journal of Chemical Physics;11/7/2007, Vol. 127 Issue 17, p174704
Academic Journal
Nuclear magnetic resonance (NMR) is a prospective means to realize quantum computers. The performance of a NMR quantum computer depends sensitively on the properties of the NMR-active molecule used, where one requirement is a large indirect spin-spin coupling over large distances. F–F spin-spin coupling constants (SSCCs) for fluorinated polyenes F–(CH==CH)n–F (n=1...5) are >9 Hz across distances of more than 10 Å. Analysis of the F,F spin-spin coupling mechanism with our recently developed decomposition of J into Orbital Contributions with the help of Orbital Currents and Partial Spin Polarization (J-OCOC-PSP=J-OC-PSP) method reveals that coupling is dominated by the spin-dipole (SD) term due to an interplay between the π lone-pair orbitals at the F atoms and the π(C2n) electron system. From our investigations we conclude that SD-dominated SSCCs should occur commonly in molecules with a contiguous π-electron system between the two coupling nuclei and that a large SD coupling generally is the most prospective way to provide large long-range spin-spin coupling. Our results give guidelines for the design of suitable active molecules for NMR quantum computers.


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