Studies on novel Cu(II) complexes of 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol and 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione: Synthesis, spectral and structural characterization

Two new mixed ligand complexes, [Cu(en)2](4-hpythol)2·2H2O (4-hpythol = 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol) (2) and [Cu(en)2(5-thot)2] (5-thot = 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione (3), have been prepared, containing en as the co-ligand. The starting ligands, potassium salts of thiohydrazide carbodithioate (RCSNHNHCSSK)/hydrazine carbodithioate (RCONHNHCSSK), underwent cyclization during the crystallization or complexation in the presence of ethylenediamine (en) and converted to 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol and 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione, respectively. The metal complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray studies. The ligand 4-hpythol and complexes 2 and 3 crystallize in the triclinic and monoclinic systems, space group P 21/n  , P1¯ and P 21/c, respectively. The ligand is present in the deprotonated thiol form in [Cu(en)2](4-hpythol)2·2H2O (2), where it is ionically bonded through the thiol sulfur atom, while potassium N′-(thiophene-2-carbonyl) hydrazinecarbodithioate after cyclization is present as the thione form in [Cu(en)2(5-thot)2] (3) and is covalently bonded through the N atom of the resulting oxadiazole-2-thione. The most noteworthy feature of 4-hpythol (1) is its existence in the thiol form in the solid state. Complex 3 show irreversible redox behavior, assignable to a M2+/M3+ one electron transfer. ESR signals were registered for complexes 2 and 3. Both complexes contain extended hydrogen bonding, providing supramolecular frameworks.

Two new complexes, [Cu(en)2](4-hpythol)2·2H2O (4-hpythol = 5-(4-hydroxy-phenyl)-1,3,4-thiadiazole-2-thiol) (2) and [Cu(en)2(5-thot)2] (5-thot = 5-thiophen-2-yl-3H-1,3,4-oxadiazole-2-thione (3), have been prepared, containing en as a co-ligand. The ligand is present in the deprotonated thiol form in [Cu(en)2](4-hpythol)2·2H2O (2) where it is ionically bonded through the thiol sulfur, while potassium N′-(thiophene-2-carbonyl) hydrazinecarbodithioate, after cyclization, is present as the thione form in [Cu(en)2(5-thot)2] (3), and is covalently bonded through the N atom of the resulting oxadiazole-2-thione. The most noteworthy feature of 4-hpythol (1) is its existence in the thiol form in the solid state.Figure optionsDownload as PowerPoint slideHighlights
► Complexes of Cu(II) with 1,3,4-thiadiazole/oxadiazole-2-thiol/thione are reported.
► Thiohydrazide carbodithioate cyclized to form thiadiazole.
► Acylhydrazine carbodithioate underwent cyclization during complexation in the presence of en and formed oxadiazole-2-thione.
► The ΔEp value for [Cu(en)2(thot)2] indicates an irreversible redox process.
► [Cu(en)2(thot)2] contains a π–π interaction between the phenyl rings of two units of the complex.