Neutron diffraction study of a very short O–H‥N hydrogen bond: crystalline adduct of 2-methylpyridine and pentachlorophenol

Abstract

In the neutron diffraction study of the 1+1 adduct 2-methylpyridine-pentachlorophenol, a very short O-H…N hydrogen bond is found with a sharply defined proton position, and distances of O-H = 1.068(7), H…N = 1.535(7) and O…N = 2.588(3) Å; the bond order of H…N is about 0.24 valence units.

Phonon driven proton transfer in crystals with short strong hydrogen bonds

“…This effect has been observed by neutron diffraction in a number of compounds: urea phosphoric acid ͑UPA͒, 6,7 pyridine-3,5-dicarboxylic acid ͑PDA͒, 8,9 1:2 cocrystal of benzene-1,2,4,5-tetracarboxylic acid and 4 , 4Ј-bipyridyl ͑BTA-BPY͒, 10 and 1:1 crystal of 2-methylpyridien and pentachlorophenol ͑4-MP-PCP͒ 11 .…”

“…The structure of the 1:1 crystal of 4-methylpyridine and pentachlorophenol was reported at low temperature by Steiner et al 11 4-MP-PCP crystallizes in a triclinic structure, in the P-1 space group with two molecules in the unit cell. The SSHB O-H¯N1 is shown in Fig.…”

The evolution of hydrogen atom parameters under changing external conditions by time-of-flight single crystal neutron diffraction

“…To examine the hydrogen atom behaviour in this group SXD was used to collect neutron diffraction data at seven temperatures in each case (20,60,100,140, 180, 220 Figure 13. Fourier synthesis carried out at 300 K, showing the carboxylic acid dimer unit in aspirin from the neutron data.…”

“…This refined well, and the hydrogen atom density found progressively to order into configuration A as the temperature is lowered, confirming A as the lower energy configuration. A similar experiment was carried out on another benzoic acid derivative, p-chlorobenzoic acid [81], at eight temperatures (20,40,80,100,133,200, 250 and 296 K), in an experiment requiring just 5 days of beam time. The structural evolution is shown in figure 10, again showing the characteristic elongation of the thermal ellipsoid of the hydrogen-bonded H atom as the temperature increases.…”

General and Theoretical Aspects of Phenols

“…Recently, neutron diffraction experiments 770 have demonstrated the existence of a very short O−H · · · N hydrogen bond in the crystalline adduct of 2-methylpyridine and pentachlorophenol which is discussed in Subsection 4.5: the O−H bond length is equal to 1.068(7)Å, the H · · · N bond length to 1.535(7)Å. Figure 57 shows the complex of 2-methylpyridine and pentachlorophenol obtained at the B3LYP/6-31G(d) computational level.…”