Molecular switching through cooperative ionic interactions and charge assisted hydrogen bonding

Sodium 2-(2-(1-cyano-2-oxopropylidene)hydrazinyl)benzenesulfonate (NaHL) was synthesized by azocoupling of diazonium salt of 2-aminobenzenesulfonic acid with 3-oxobutanenitrile and characterized by IR, 1H and 13C NMR spectroscopies and ESI-MS analysis. In dimethylsulfoxide-d6 solution NaHL exists as a mixture of Z- and E-hydrazone forms in the amounts of 96 and 4%, respectively. Treatment of this isomeric mixture with copper(II) nitrate hydrate in the presence of ethylenediamine (en) provides unusual (E,Z) → E switching of NaHL to give [Cu(H2O)2(en)2](HL)2 (1). The process is interpreted on the basis of cooperative ionic interactions and resonance assisted hydrogen bonding (RAHB) → charge assisted hydrogen bonding (CAHB) transition. © 2016 Elsevier Ltd