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 M.K. Bharty a,⇑ , A. Bharti a , R.K. Dani a , S.K. Kushawaha a , R. Dulare b , N.K. Singh a,⇑ a Department of Chemistry, Banaras Hindu University, Varanasi 221005, India b Department of Chemistry, P.G. College, Ghazipur, India article info Article history: Received 15 March 2012 Accepted 17 April 2012 Available online 3 May 2012 Keywords: Thiadiazole complex Oxadiazole complex Copper(II) complexes Mixed ligand complexes Supramolecular architecture abstract Two new mixed ligand complexes, [Cu(en) 2 ](4-hpythol) 2 2H 2 O (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 thiohy- drazide carbodithioate (RCSNHNHCSSK)/hydrazine carbodithioate (RCONHNHCSSK), underwent cycliza- tion 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, mag- netic susceptibility and single crystal X-ray studies. The ligand 4-hpythol and complexes 2 and 3 crystal- lize in the triclinic and monoclinic systems, space group P 21/n, P  1 and P 21/c, respectively. The ligand is present in the deprotonated thiol form in [Cu(en) 2 ](4-hpythol) 2 2H 2 O(2), where it is ionically bonded through the thiol sulfur atom, while potassium N 0 -(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 M 2+ /M 3+ one electron transfer. ESR signals were registered for complexes 2 and 3. Both complexes contain extended hydrogen bonding, providing supramolecular frameworks. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Copper exhibits considerable biochemical action in humans, either as an essential trace metal or as a constituent of various exogenously administered compounds. In its former role it is bound to ceruloplasmin, albumin and other proteins, while in the latter it is bound to ligands of various types forming complexes that interact with biomolecules, mainly proteins and nucleic acids. In particular, the involvement of copper in human diseases has been described from a medicinal-chemical [1] and a biochemical view [2], focusing on the molecular physiology of Cu transport [3]. Current interest in copper complexes is stemming from their potential use as antimi- crobial, antiviral, anti-inflammatory, antitumor agents, enzyme inhibitors or chemical nucleases. Markedly, the biochemical action of copper complexes with non-steroidal anti-inflammatory drugs (NSAIDs) has been studied [4], which have reduced side effects, and their mode of action is attributed to their marked superoxide-dismutase (SOD) mimetic activity. Copper-based compounds show potential chemotherapeutic properties [5,6]. The toxic effects of copper complexes lead to cell death either by necrosis or through the activation of the apoptotic process [7]. 1,3,4-Thiadiazole and oxadiazole derivatives, which belong to an important group of heterocyclic compounds, are the subject of extensive study in recent years because of their diverse biological activities, such as anti-tuberculostatic, anti-inflammatory, analge- sic, antipyretic, anticonvulsant, antibacterial and antifungal activi- ties [8–13]. These compounds have also been shown to exhibit antimycotic [14] and analgesic action [15]. Some works have reported on the metal complexes of 2,5-bis(2-pyridyl)-1,3, 4-thiadiazole [16], 5-phenyl-1,3,4-oxadiazole-2-thione [17,18], 5- (4-pyridyl)-1,3,4-oxadiazole-2-thione [19–20], 5-(3-pyridyl)-1,3, 4-oxadiazole-2-thione [21] and 5-(2-pyridyl)-1,3,4-oxadiazole-2- thione [22], but no work seems to have been carried out on the com- plexes of 1,3,4-thiadiazoles-2-thiones/thiols. Therefore it would be of interest to investigate the mixed ligand complexes of thiadiazole- 2-thiol and oxadiazoles-2-thiones and to compare the mode of bonding of the ligands and structures of the complexes. In view of this, we have prepared and characterized the Cu(II) complexes 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.04.025 ⇑ Corresponding authors. Tel.: +91 542 6702452. E-mail addresses: mkbharty@bhu.ac.in (M.K. Bharty), singhnk_bhu@yahoo.com (N.K. Singh). Polyhedron 41 (2012) 52–60 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly