TY - JOUR

T1 - NMR studies of solid pentachlorophenol-4-methylpyridine complexes exhibiting strong OHN hydrogen bonds

T2 - Geometric H/D isotope effects and hydrogen bond coupling cause isotopic polymorphism

AU - Ip, Brenda C.K.

AU - Shenderovich, Ilya G.

AU - Tolstoy, Peter M.

AU - Frydel, Jaroslaw

AU - Denisov, Gleb S.

AU - Buntkowsky, Gerd

AU - Limbach, Hans Heinrich

PY - 2012/11/26

Y1 - 2012/11/26

N2 - We have studied the hydrogen bond interactions of 15 N labeled 4-methylpyridine (4-MP) with pentachlorophenol (PCP) in the solid state and in polar solution using various NMR techniques. Previous spectroscopic, X-ray, and neutron crystallographic studies showed that the triclinic 1:1 complex (4-MPPCP) exhibits the strongest known intermolecular OHN hydrogen bond in the solid state. By contrast, deuteration of the hydrogen bond gives rise to the formation of a monoclinic structure exhibiting a weaker hydrogen bond. By performing NMR experiments at different deuterium fractions and taking advantage of dipolar 1 H- 15 N recoupling under combined fast MAS and 1 H decoupling, we provide an explanation of the origin of the isotopic polymorphism of 4-MPPCP and improve previous chemical shift correlations for OHN hydrogen bonds. Because of anharmonic ground state vibrations, an ODN hydrogen bond in the triclinic form exhibits a shorter oxygen-hydron and a longer oxygen-nitrogen distance as compared to surrounding OHN hydrogen bonds, which also implies a reduction of the local dipole moment. The dipole-dipole interaction between adjacent coupled OHN hydrogen bonds which determines the structure of triclinic 4-MPPCP is then reduced by deuteration, and other interactions become dominant, leading to the monoclinic form. Finally, the observation of stronger OHN hydrogen bonds by 1 H NMR in polar solution as compared to the solid state is discussed.

AB - We have studied the hydrogen bond interactions of 15 N labeled 4-methylpyridine (4-MP) with pentachlorophenol (PCP) in the solid state and in polar solution using various NMR techniques. Previous spectroscopic, X-ray, and neutron crystallographic studies showed that the triclinic 1:1 complex (4-MPPCP) exhibits the strongest known intermolecular OHN hydrogen bond in the solid state. By contrast, deuteration of the hydrogen bond gives rise to the formation of a monoclinic structure exhibiting a weaker hydrogen bond. By performing NMR experiments at different deuterium fractions and taking advantage of dipolar 1 H- 15 N recoupling under combined fast MAS and 1 H decoupling, we provide an explanation of the origin of the isotopic polymorphism of 4-MPPCP and improve previous chemical shift correlations for OHN hydrogen bonds. Because of anharmonic ground state vibrations, an ODN hydrogen bond in the triclinic form exhibits a shorter oxygen-hydron and a longer oxygen-nitrogen distance as compared to surrounding OHN hydrogen bonds, which also implies a reduction of the local dipole moment. The dipole-dipole interaction between adjacent coupled OHN hydrogen bonds which determines the structure of triclinic 4-MPPCP is then reduced by deuteration, and other interactions become dominant, leading to the monoclinic form. Finally, the observation of stronger OHN hydrogen bonds by 1 H NMR in polar solution as compared to the solid state is discussed.

UR - http://www.scopus.com/inward/record.url?scp=84870040761&partnerID=8YFLogxK

U2 - 10.1021/jp305863n

DO - 10.1021/jp305863n

M3 - Article

C2 - 22861155

AN - SCOPUS:84870040761

VL - 116

SP - 11370

EP - 11387

JO - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 46

ER -