Using QTAIM we show that the hydrogen bonding complexes of 5-halogenated-1-methyluracil (XmU; X = F, CI, Br, I or At) with a water molecule were always stronger than the corresponding halogen bonds. The strength of the hydrogen bond decreased with increasing halogen size. The hydrogen bonds displayed an admixture of covalent character but all the halogen bonds were purely electrostatic in nature. An F---O halogen bond was found and was facilitated by an intermediate F---H bonding interaction. The metallicity xi(r(b)) of the C = 0 bonds neighboring the hydrogen bonds and of the C-X bonds contiguous with the halogen bonds was explored. (C) 2016 Elsevier B.V. All rights reserved.