Determining the geometry of hydrogen bonds in solids with picometer accuracy by quantum-chemical calculations and NMR spectroscopy.
The structure of multiply hydrogen-bonded systems is determined with picometer accuracy by a combined solid-state NMR and quantum-chemical approach. On the experimental side, advanced 1H-15N dipolar recoupling NMR techniques are capable of providing proton-nitrogen distances of up to about 250 pm with an accuracy level of +/-1 pm for short distances (i.e., around 100 pm) and +/-5 pm for longer ones (i.e., 180 to 250 pm). The experiments were performed under fast magic-angle spinning, which ensures sufficient dipolar decoupling and spectral resolution of the 1H resonance lines. On the quantum-chemical side, the structures of the hydrogen-bonded systems were computationally optimised, yielding complete sets of nitrogen-proton and proton-proton distances, which are essential for correctly interpreting the experimental NMR data. In this way, nitrogen-proton distances were determined with picometer accuracy, so that vibrational averaging effects on dipole-dipole couplings need to be considered. The obtained structures were finally confirmed by the complete agreement of computed and experimental 'H and '5N chemical shifts. This demonstrates that solid-state NMR and quantum-chemical methods ideally complement each other and, in a combined manner, represent a powerful approach for reliable, high-precision structure determination whenever scattering techniques are inapplicable.
Schulz-Dobrick
Martin
M
Max Planck Institute for Polymer Research Postfach 3148, 55021 Mainz, Germany.
Metzroth
Thorsten
T
Spiess
Hans Wolfgang
HW
Gauss
Jürgen
J
Schnell
Ingo
I
D002627:Chemistry, Physical / Q000379:methods*; D018360:Crystallography, X-Ray; D019281:Dimerization; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D015233:Models, Statistical; D008962:Models, Theoretical; D009584:Nitrogen / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D011522:Protons; D015203:Reproducibility of Results; D012542:Scattering, Radiation
D009587:Nitrogen Isotopes; D011522:Protons; D009584:Nitrogen; D010100:Oxygen