Polymeric Cd(II), trinuclear and mononuclear Ni(II) complexes of 5- methyl-4-phenyl-1,2,4-triazole-3-thione: Synthesis, structural characterization, thermal behaviour, fluorescence properties and antibacterial activity M.K. Bharty a, * , S. Paswan a , R.K. Dani a , N.K. Singh a , V.K. Sharma b , R.N. Kharwar b , R.J. Butcher c a Department of Chemistry, Banaras Hindu University, Varanasi, 221005, India b Department of Botany, Banaras Hindu University, Varanasi, 221005, India c Department of Chemistry, Howard University, 525 College Street NW, Washington, DC, 20059, USA article info Article history: Received 15 June 2016 Received in revised form 19 September 2016 Accepted 7 October 2016 Available online 8 October 2016 Keywords: 1,2,4-Triazole complexes Supramolecular architecture Antibacterial activity TGA Fluorescent properties abstract Syntheses of a polymeric Cd(II) complex, [Cd(mptt) 2 ] n (1), a trinuclear Ni(II) complex, [Ni 3 (m-mptt) 4 (m- H 2 O) 2 (H 2 O) 2 (ttfa) 2 ]$3H 2 O(2) and a mononuclear Ni(II) complex [Ni(mptt) 2 (en) 2 ](3) have been per- formed using the ligand 5-methyl-4-phenyl-1,2,4-triazole-3-thione (Hmptt) and nickel(II)/cadmium(II) salts {ttfa ¼ thenoyltrifluroacetonate). The ligand and the complexes have been characterized by various physicochemical methods in addition to their single crystal X-ray structure. The Cd centre in complex 1 adopts a distorted tetrahedral geometry with one sulfur atom and two mptt ligands provide three ni- trogen atoms from three triazole units. The sulfur atom of the ligand binds covalently and overall the ligand acts as uninigative N,S/N,N bidentate moiety. The polymeric structure of complex 1 results from the N atoms of the neighboring triazole units coordinating with the Cd(II) centre. The three Ni(II) centres in the trinuclear Ni(II) complex 2 form a linear arrangement and all have six coordinated arrangements. The middle Ni(II) binds with four deprotonated triazole ring nitrogens and two water molecules form two bridges. The terminal Ni(II) centres bind through two thenoyl oxygens, two triazole nitrogens and water molecules that formed bridges with the middle Ni centre. In complex 3, the nickel(II) centre is covalently bonded through two deprotonated triazole ring nitrogens from two ligand moieties and other four sites are occupied by four nitrogens from two bidentate en ligands. Thermogravimetric analyses (TGA) of the complexes indicated for NiO as the final residue. The bioefficacy of the ligand and complexes 2 and 3 have been examined against the growth of bacteria to evaluate their anti-microbial potential. Complex 2 showed high antibacterial activity as compared to the ligand and complex 3. Complexes 1 , 2 and 3 are fluorescent materials with maximum emissions at 425, 421 and 396 nm at an excitation wavelength of 323, 348 and 322 nm, respectively. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The coordination chemistry of nitrogen-sulfur containing het- erocyclic ligands such as 1,2,4-triazoles and their derivatives con- taining HNCS moiety, is an emerging and rapidly developing area of research [1e3]. Synthesis of 1,2,4-triazoles and their derivatives has attracted considerable attention due to their potential biological activity and agricultural applications [4e8]. These nitrogen-sulfur heterocyclic systems have received considerable interest as li- gands in the formation of coordination compounds because they have capacity to form s bond as well as p bonds in the same system [9]. These compounds have received much attention due to their important pharmacological activities, such as antiviral, analgesic, antimicrobial, antidepressant and antifungal effects [10e12]. 1,2,4- Triazoles may provide multidentate coordination sites and link more than one metal centre which may provide p-p stacking be- tween the rings to generate multi-nuclear complexes [13,14]. Thus, * Corresponding author. Tel.: þ91 5426702447; fax: þ91 542 2368127. E-mail address: mkbharty@bhu.ac.in (M.K. Bharty). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc http://dx.doi.org/10.1016/j.molstruc.2016.10.030 0022-2860/© 2016 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1130 (2017) 181e193