Spectrochimica Acta Part A 75 (2010) 585–588 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Synthesis and spectral investigations of Mn(II) complexes of pentadentate bis(thiosemicarbazones) Suja Krishnan, K. Laly, M.R. Prathapachandra Kurup ∗ Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India article info Article history: Received 28 March 2009 Received in revised form 10 November 2009 Accepted 10 November 2009 Keywords: 2,6-Diacetylpyridine Bis(thiosemicarbazones) Manganese(II) complexes EPR studies abstract Five Mn(II) complexes of bis(thiosemicarbazones) which are represented as [Mn(H 2 Ac4Ph)Cl 2 ] (1), [Mn(Ac4Ph)H 2 O] (2), [Mn(H 2 Ac4Cy)Cl 2 ]·H 2 O (3), [Mn(H 2 Ac4Et)Cl 2 ]·3H 2 O (4) and [Mn(H 2 Ac4Et)(OAc) 2 ]·3H 2 O (5) have been synthesized and characterized by elemental analyses, electronic, infrared and EPR spectral techniques. In all the complexes except [Mn(Ac4Ph)H 2 O], the ligands act as pentadentate neutral molecules and coordinate to Mn(II) ion through two thione sulfur atoms, two azomethine nitrogens and the pyridine nitrogen, suggesting a heptacoordination. While in compound [Mn(Ac4Ph)H 2 O], the dianionic ligand is coordinated to the metal suggesting six coordination in this case. Magnetic studies indicate the high spin state of Mn(II). Conductivity measurements reveal their non-electrolyte nature. EPR studies indicate five g values for [Mn(Ac4Ph)H 2 O] showing zero field splitting. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The synthesis and study of coordination complexes with unusual geometry and coordination number is a challenging task for the practical chemist. The most important factor in this objec- tive is probably the design of ligands with an appropriate structural backbone that can coerce the metal ion into the desired coordi- nation geometry. Though tridentate ligands with mixed NS donor points at strategic positions of the donor-framework are common [1,2], such pentadentate ligands are seldom encountered in coordi- nation chemistry. The chelating properties of 2,6-diacetylpyridine bis(thiosemicarbazone), have been investigated and several coor- dination modes have been found [3–6]. There are reports on heptacoordinated bis(thiosemicarbazones) of 2,6-diacetylpyridine [7]. This type of coordination is commonly found in metals like Sn(IV) [8], Mn(II) [9] and indium(III) [10]. As previous research [11] show, these ligands tend to form pentagonal bipyramidal complexes in which the ligand acts as a pentacoordinated chelate and the two arms (thiosemicarbazide groups) of the ligand have remained protonated [12]. Transition metal complexes of bis(thiosemicarbazone) lig- ands have been investigated as metallodrugs for a number of years. It has been reported that -diketone and -ketoaldehyde bis(thiosemicarbazones) and their metal complexes show anti- ∗ Corresponding author. Tel.: +91 484 2862423; fax: +91 484 2575804. E-mail addresses: mrp@cusat.ac.in, mrp k@yahoo.com (M.R. Prathapachandra Kurup). tumor activity [13,14]. Spectral and biological studies have been carried out on metal complexes of 2,6-diacetylpyridine bis(N4-substituted thiosemicarbazones)[15]. Manganese coordi- nation chemistry with a diverse range of ligands has much relevance in biological systems with a number of model man- ganese complexes. Manganese coordination compounds are also of growing importance as homogeneous catalysts in oxidation reac- tions [16,17]. In such studies manganese complexes in different oxidation states were obtained and their magnetic and spectral properties were studied in depth. The absence of ligand field stabilization energy for high spin Mn(II) complexes leads to the possibility to obtain various coordination geometries and a lower stability of Mn(II) complexes compared with those of other divalent 3d metals. In the present article, synthesis and characterization of some 2,6-diacetylpyridine bis(N4-substitutedthiosemicarbazones) and their Mn(II) complexes are investigated with the help of physico- chemical techniques. 2. Experimental 2.1. Materials 2,6-Diacetylpyridine (Aldrich), hydrazine hydrate, N4-phenyl isothiocyanate, N4-cyclohexyl isothiocyanate, N4-ethylthiosemi- carbazide, manganese(II) chloride tetrahydrate and manganese(II) acetate tetrahydrate were used as supplied for the preparation of complexes. Solvents used were methanol, ethanol, dimethylfor- mamide and chloroform. 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.11.022