Double quadrupole resonance study of the pyridine + water complex

Abstract

A water + pyridine complex is formed at temperatures below 190 K. Using double nuclear resonance techniques the ²D, ¹⁴N and ¹⁷O nuclear quadrupole resonance spectra of isotopically enriched examples of this complex have been measured at 77 K. From these data it may be deduced that the complex consists of 4 water molecules and 1 pyridine molecule and that one proton of the first water molecule is hydrogen bonded to the lone pair of the pyridine nitrogen atom with an N⋯H hydrogen bond of 1.8 ± 0.2 Å. The second proton of this water molecule is hydrogen bonded to the oxygen of the second molecule in a configuration like that of water in ice. The second water molecule is almost exactly ice-like and each of its protons is hydrogen bonded to the oxygen atoms of the third and fourth water molecules which are equivalent. These two water molecules are only very weak hydrogen bond donors with O–H bond lengths around 0.97 Å.