AN UNUSUAL GEOMETRICAL AND SPECTROSCOPIC ISOTOPIC EFFECT IN THE SOLID COMPLEX OF 4-METHYLPYRIDINE WITH PENTACHLOROPHENOL

The structure of the complex of 4-methylpyridine with deuterated pentachlorophenol (MP PCP-d) has been determined by X-ray diffraction. The crystals are monoclinic, space group Cc, with a=3.942(3), b=27.73(3), c=13.297(9) Å,β=101.81(6)° and Z=4. The structure, solved by direct methods, has been refined to R=0.036 for 3600 non-zero (hkl) (hkl) reflections. The crystals of MP PCP-d are non-isomorphous with the complex MP PCP. The OD group is engaged in a bifurcated interaction to give OD⋯N and OD⋯Cl(6) hydrogen bonds with lengths 2.638(3) and 3.002(3) Å and angles 141(4) and 115(4)°, respectively. The anomalous spectroscopic isotopic ratio ν )OHN)/ν(ODN) is lower than 1 and has been explained by drastic changes in the hydrogen bridge geometry. © 1990.