Experimental evidence of Chalcogen bonding at oxygen
An o-nitro-O-aryl oxime was observed to exhibit a short O...O contact, which exhibited characteristics consistent with a chalcogen bond. Topological analysis of the experimental electron density of two analogues shows the presence of a bond path between the two oxygen atoms, with r(r) and Ñ2r(r) value consistent with an electrostatic interaction. NBO calculations indicate the presence of a small n(O) s* (O-N) orbital delocalisation worth 1.13 kcal/mol. Finally, electrostatic potential calculations indicate the presence of a s-hole, the "smoking gun" indicating a Ch bond. These results are unusual as oxygen is not typically considered to be a Ch-bond donor, especially in relatively unactivated systems such as oximes.