Ring to open-chain transformation induced by selective metal coordination in a new dithiocarbazate ligand

• We have prepared a new dithiocarbazate tetradentate chelate ligand (N, N, S, S).
• The compound can exist in two isomeric forms: an open form and a cyclized form.
• The cyclic form is obtained in the crystals and is the only one detected in solution.
• The transformation of the cyclic into the open ligand form is observed with some metal ions.

By unsymmetrical derivatization of acetylacetone with S-ethyl-dithiocarbazide, a new tetradentate chelate ligand (N, N, S, S) has been prepared and studied. The compound can exist in two isomeric forms: an open tetradentate chelating form and a cyclic dihydropyrazole form. The cyclic form is obtained in the solid state and is the only one detected even in solution. However, in the presence of metal ions, a competition between intramolecular cyclization and metal complexation of the open form is active, and monochelate square planar complexes can be obtained through transformation of the cyclized into the open ligand form. We have proved this with metal ions prone to square planar coordination such as Ni(II) and Pd(II). On the other hand, with VO(II), Pb(II), UO2(II), La(III), Ce(III), no complex was obtained and the cyclized form was recovered from the reaction mixture. This indicates some selectivity of the ligand towards specific metal ions.

The compound exists in two isomeric forms: an open-chain and a cyclic dihydropyrazole form. The cyclic form is found in crystals and in solution. In the presence of suitable metal ions, a competition between cyclization and complexation is active. Complexes are obtained through transformation of the cyclized into the open form.Figure optionsDownload as PowerPoint slide