Two-bond 19F-15N spin-spin coupling constants (2hJF-N) across F-H•••N hydrogen bonds

Equation-of-motion coupled cluster calculations (EOM-CCSD) have been performed to determine two-bond F-19-N-15 spin-spin coupling constants ((2h)J(F-N)) for thirteen neutral complexes stabilized by F- H...N hydrogen bonds. The proton acceptors include nitrogens that are sp (HCN and its derivatives), sp(2) (aromatic azines), and sp(3) (NH3 and its derivatives) hybridized. (2h)J(F-N) is determined by the Fermi-contact term, which is strongly dependent on the intermolecular F-N distance but varies only slightly with small perturbations of the hydrogen bond from linearity. (2h)J(F-N) is more sensitive to the hybridization and bonding at the nitrogen in F-H...N hydrogen bonds than is (2h)J(F-N) for complexes stabilized by N-H-N and N-H+-N hydrogen bonds. As a result, (2h)J(F-N) at the same F-N distance for different complexes can vary by 10-15 Hz, and this reduces the quality of the quadratic curve used to relate (2h)J(F-N) to the F-N distance. However, if the complexes are grouped according to the hybridization of the nitrogen, excellent quadratic correlations are found between (2h)J(F-N) and the F-N distance. Moreover, if the same groupings are used, (2h)J(F-N) also correlates with the charge density at the bond critical point of the hydrogen bond.