Chalcogen and Hydrogen Bond Team up in Driving Anion⋅⋅⋅Anion Self-Assembly

H-selenite anions (HSeO3-) form in the solid unprecedented anionic supramolecular chains wherein single units are assembled via alternating short Se & sdot;& sdot;& sdot;O and H & sdot;& sdot;& sdot;O contacts. Crystallographic analyses and computational studies (the quantum theory of "atoms-in-molecules", QTAIM, and the noncovalent interaction plot, NCIPlot) consistently prove the attractive nature of these chalcogen bonds (ChBs) and hydrogen honds (HBs), the Janus-type character of HSeO3- anions which act as both donors and acceptors of ChB and HB, and the possible stability of anion dimers in solution. The effectiveness of the ChBs herein described may lead to consider the HSeO3- moiety as a new entry in the toolbox of crystal engineering based on ChB.