The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP---PCP) and its deuterated analogue (MP---PCP-d) were determined at 80 K by X-ray diffraction. The MP---PCP complex crystallizes in the space group with a = 7.267(7), b = 8.966(9), c = 13.110(14) Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP---PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12) Å, β = 101.38(9)° and Z = 4. The O…H…N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D…N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.