LOCATION OF THE PROTON IN THE VERY STRONG OHO HYDROGEN-BONDS IN -(N,N-DIETHYLAMINO-N-OXYMETHYL)-4,6-DICHLOROPHENOL - A SINGLE-CRYSTAL NEUTRON-DIFFRACTION STUDY

The crystal structure of -(N,N-diethylamino-N-oxymethyl)-4,6-dichlorop henol contains two slightly different molecules A and B, both with ver y strong intramolecular O ... H ... O hydrogen bonds, with O-O distanc es 2.423(4) Angstrom and 2.400(5) Angstrom, respectively, and with no crystallographic symmetry. The bridging oxygen atoms are also chemical ly different, O1 is bonded to carbon and O2 to nitrogen. The single cr ystal neutron diffraction study shows quite unambiguously that the pro ton in both cases is located slightly off-centred. In the A molecule O 1-H = 1.167(6) Angstrom, H-O2 = 1.258(6) Angstrom and the angle O-H-O = 175.8(5)degrees; in the B molecule O1-H = 1.186(7) Angstrom, H-O2 = 1.214(7) Angstrom and the angle O-H-O = 176.5(5)degrees. As expected t he proton is thus closer to the centre in the slightly shorter hydroge n bond.