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

Illusive Au<sup>I/III</sup>···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<sup>I/III</sup>···H contacts, a solid spectroscopic evidence for Au<sup>I/III</sup>···H bonding has been missing. Recently<a></a><a>, Bakar <i>et al.</i></a> (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 [Au<sub>6</sub>]<sup>2+</sup>and observing the <sup>1</sup>H (<sup>13</sup>C) NMR resonances at relevant H(C) nuclei deshielded with respect to precursor compound, the authors concluded with reservations that <i>“the present Au···H–C interaction is a kind of “hydrogen bond”, where the [Au<sub>6</sub>]<sup>2+</sup>serves as an acceptor”</i>. Here, we show that the Au<sub>6</sub>cluster 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 of<b></b>the 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 .