Syntheses, spectral and crystallographic studies of novel monometallic Co(II) and Zn(II) complexes with phenyl-(5-pyridin-4-yl[1,3,4]thiadiazol-2-yl)-amine Ram Dulare, S.K. Kushawaha, M.K. Bharty, N.K. Singh ⇑ Department of Chemistry, Banaras Hindu University, Varanasi 221 005, India article info Article history: Received 21 July 2010 Received in revised form 6 September 2010 Accepted 6 September 2010 Available online 18 September 2010 Keywords: 1,3,4-Thiadiazole Co(II) and Zn(II) complexes p–p stacking Supramolecular architecture abstract Two novel monometallic complexes [Co(ppt)(SO 4 )(H 2 O) 4 )]ÁH 2 O(1) and [Zn(ppt) 2 (CH 3 COO) 2 (H 2 O) 2 ]Á(2) of ppt = phenyl-(5-pyridin-4-yl[1,3,4]thiadiazol-2-yl)-amine have been synthesized and their structures investigated by elemental analyses, IR, UV–Vis., magnetic susceptibility and single crystal X-ray. The geometry of both complexes are distorted octahedral. The p–p and CAHÁÁÁp interactions play important role along with hydrogen bonding to form host–guest cavity. The hydrogen-bonding interactions between adjacent layers extend these structures to overall 3D supramolecular architectures. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The derivatives of 2-amino-[1,3,4]thiadiazole, depending on the nature of substituents can be found as a structural fragment of drugs and herbicides with a wide spectrum of activity due to the presence of the toxiphocic AN@CASA linkage [1]. They are known as the car- bonic anhydrase inhibitors and some of them possess antimycobac- terial, anasthetic, antidepressant, anxiolytic [2–7], anti- inflammatory [8], anticonvulsant [9,10], antihypertensive [11] and anticancer [12] activities. They also find applications in agriculture, material chemistry [13] and are also useful as corrosion inhibitors [14]. Derivatives of 1,3,4-thiadiazoles were synthesized by intramo- lecular cyclization of substituted thiosemicarbazides under acidic condition. Due to the presence of aromatic pyridine, phenyl and 1,3,4-thiadiazole ring in the ligand under investigation, p–p stack- ing is envisaged in the present system [15]. The bent organic com- pounds such as 2,5-bis(4-pyridyl)-[1,3,4]thiadiazole, a member of crystal engineering family, has recently focused interest because of several characteristics: (i) the bent ligand has flexible coordina- tion modes and (ii) longer ligand will lead to larger voids. The phe- nyl-(5-pyridin-4-yl[1,3,4]thiadiazol-2-yl)-amine (ppt) being investigated here is longer than those containing planar centers and has potential biological activities due to the presence of thiadi- azole ring [16]. With an aim of obtaining information about the chemical and structural properties of the metal complexes, espe- cially in reference to stereochemistry and the effects of coordination on the conformation of the thiadiazole, we have undertaken the studies of two new complexes of Co(II) and Zn(II) obtained from a new ligand phenyl-(5-pyridin-4-yl[1,3,4]thiadiazol-2-yl)-amine (ppt). 2. Experimental 2.1. Chemical and starting materials Commercial reagents were used without further purification and all experiments were carried out in open atmosphere. Isonicot- inic acid hydrazide (Sigma–Aldrich) and phenyl isothiocyanate (Fluka Chemicals, Switzerland) were used as received. All solvents were purchased from Merck Chemicals, India, dried and distilled before use by following standard procedure. 2.2. Physical measurements Carbon, hydrogen and nitrogen contents were estimated on a CHN Model CE-440 Analyzer and on an Elementar Vario EL III Carlo Erba 1108. By following standard procedures, the complexes were analysed for their metal content, after decomposition with a mix- ture of conc. HNO 3 and HCl, followed by conc. H 2 SO 4 [17]. Magnetic susceptibility measurements were performed at room temperature on a Cahn Faraday balance using Hg[Co(NCS) 4 ] as the calibrant and electronic spectra were recorded on SIMADZU 1700 UV–Vis. spec- trophotometer in DMSO. IR spectra were recorded in the 4000– 400 cm À1 region as KBr pellets on a Varian Excalibur 3100 FT-IR spectrophotometer. 1 H and 13 C NMR spectra were recorded in 0022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2010.09.012 ⇑ Corresponding author. Tel.: +91 542 2318529; fax: +91 542 2368127. E-mail addresses: singhnk_bhu@yahoo.com, nksingh@bhu.ac.in (N.K. Singh). Journal of Molecular Structure 984 (2010) 96–101 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc