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Correspondence: Hydrogen Bond to Gold? 1H NMR is Not a Proof of Hydrogen Bonds in Transition Metal Complexes
preprintsubmitted on 13.12.2018, 09:23 and posted on 13.12.2018, 17:33 by Jan Vícha, Cina Foroutan-Nejad, Michal Straka
Illusive AuI/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 AuI/III···H contacts, a solid spectroscopic evidence for AuI/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 .