Correspondence: Hydrogen Bond to Gold? 1H NMR is Not a Proof of Hydrogen Bonds in Transition Metal Complexes

Illusive Au^I/III···H hydrogen bonds and their effect on structure and dynamics of molecules have been a matter of debate. While a number of X-ray studies reported gold compounds with short Au^I/III···H contacts, a solid spectroscopic evidence for Au^I/III···H bonding has been missing. Recently, Bakar et al. (NATURE COMMUNICATIONS 8:576) reported compound with four short Au···H contacts (2.61­–2.66 Å; X-ray determined). Assuming the central cluster be [Au₆]²⁺and observing the ¹H (¹³C) NMR resonances at relevant H(C) nuclei deshielded with respect to precursor compound, the authors concluded with reservations that “the present Au···H–C interaction is a kind of “hydrogen bond”, where the [Au₆]²⁺serves as an acceptor”. Here, we show that the Au₆cluster in their compound bears negative charge and the Au···H contacts lead to a weak (~1 kcal/mol) auride···hydrogen bonding interactions, though unimportant for the overall stability ofthe molecule. Additionally, computational analysis of NMR chemical shifts reveals that the deshielding effects at respective hydrogen nuclei are not directly related to Au···H–C hydrogen bonding .