An unusual intermolecular interaction between a lone pair and an electron-rich π-electron system of a quinoid dianion

International audience; The crystal structure of lithium 2,5-dihydroxyquinonate dihydrate bis(dimethylsulfoxide) solvate [Li2DHQ(H2O)2(DMSO)2] reveals a close contact between the lone pair on the electropositive S atom of DMSO and the dianionic quinoid ring. This contact, resembling a π-hole interaction involving a dianion as an acceptor was studied in detail by a combination of X-ray charge density and quantum chemical modelling. Topology of electron density reveals a bond path and a (3,-1) critical point between the S atom of the DMSO and a C atom of the quinoid ring, while analysis of electrostatic potential indicates that the interaction between these two atoms is repulsive. However, the global electrostatic interaction between the DMSO and the dihydroxyquinonate moieties is attractive (-19.1 kJ/mol), as well as total in vacuo interaction energy (-42.8 kJ/mol).