Adjusting the balance between hydrogen and chalcogen bonds

A complex is assembled which pairs a carboxyl group of X 1 COOH with a 1,2,5-chalcogenadiazole ring containing substituents on its C atoms. The OH of the carboxyl group donates a proton to a N atom of the ring to form a OH N H-bond (HB), while its carbonyl O engages in a Y O chalcogen bond (ChB) with the ring in which Y = S, Se, Te. The ChB is strengthened by enlarging the size of the Y atom from S to Se to Te. Placement of an electron-withdrawing group (EWG) X 1 on the acid strengthens the HB while weakening the ChB; the reverse occurs when EWGs are placed on the ring. By selection of the proper substituents on the two units, it is possible to achieve a near perfect balance between the strengths of these two bonds. These bond strengths are also reflected in the NMR spectroscopic properties of the chemical shielding of the various atoms and the coupling between the nuclei directly involved in each bond. The balance between the H-bond and chalcogen bond can be precisely tuned by adjustment of the substituents and nature of Ch atom: S, Se, or Te. Either bond can be selectively strengthened at the expense of the other.