Novel binuclear Cu(II) complexes combining a semicarbazone Schiff base with distinct bridging ligands: Structure and antimicrobial activity Behrouz Shaabani a,⇑ , Ali Akbar Khandar a , Farzaneh Mahmoudi a , Miguel Anxo Maestro b , Salete S. Balula c , Luís Cunha-Silva c,⇑ a Department of Inorganic Chemistry, Faculty of Science, Tabriz University, 51666-14766 Tabriz, Iran b Departamento de Química Fundamental, Universidade da Coruña, Campus da Zapateira s/n, 15071 A Coruña, Spain c REQUIMTE & Department of Chemistry and Biochemistry, Faculty of Chemistry, University of Porto, 4169-007 Porto, Portugal article info Article history: Received 12 March 2013 Accepted 8 April 2013 Available online 15 April 2013 Keywords: Binuclear complexes Coordination Crystal structures Antimicrobial activity abstract The Schiff base methyl 2-pyridyl ketone semicarbazone (HL) was prepared from the condensation of methyl 2-pyridyl ketone and semicarbazide, and used in the synthesis of a series of novel binuclear Cu(II) complexes with three distinct bridging ligands: [Cu(L)(l 1,1 -N 3 )] 2 (1), [Cu(L)(l S,N -SCN)] 2 (2) and [Cu(L)(Cl)] 2 (3). The compounds were characterized by elemental analysis, IR and UV–Vis spectroscopy, and their solid-state structures have been established by single-crystal X-ray diffraction revealing the first binuclear complexes with the HL ligand. Supramolecular interactions invoving the adjacent com- plexes were studied in detail. The antimicrobial activity of HL and the complexes 1–3 was further inves- tigated against the bacteria Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Erwinia carotovora and fungals Candida kefyr, Candida krusei and Aspergillus niger, with the complex 3 demonstrating enhanced activity relatively to the free ligand and remaining complexes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Schiff base ligands are ubiquitous in coordination chemistry being used in the synthesis of a large variety of transition metal complexes, which remains an important area of research due to their simple synthesis, good yield, high purity and wide range of applications [1–9]. Semicarbazone based ligands are versatile mol- ecules and can coordinate to metal either as neutral or anionic forms [10]. This family of molecules have been demonstrating high potential in numerous applications such as anticancer, antibacte- rial, antifungal, antivirus agents [11–16]. Usually their metal com- plexes revealed enhanced antimicrobial activities than free Schiff base ligands [16–19]. Pseudohalides (N 3 À , NCS À , NCO À ) are known as extremely versatile ligands in coordination chemistry [20–23] and as bridging ligands, they can form a rich structural variety of polynuclear complexes with interesting magnetic properties [9,21–25]. The bridging modes strongly influence the magnetic interactions between adjacent metal ions, ranging from antiferro- magnetic to ferromagnetic couplings [25–32]. In this paper, we re- port the synthesis and characterization of the Schiff base ligand methyl 2-pyridyl ketone semicarbazone (HL; Scheme 1), which was used in the preparation of unprecedented binuclear copper(II) complexes in combination with azide, thiocyanate and chlorine as bridging ligands, [Cu(L)(l 1,1 -N 3 )] 2 (1), [Cu(L)(l S,N -SCN)] 2 (2) and [Cu(L)(Cl)] 2 (3). The effects of different bridging ligands on the structures and property of the complexes were explored, and their antimicrobial activity was further investigated. 2. Experimental 2.1. Materials and methods All chemicals and solvents were purchased from Merck or Fluka and were used without purification. Microanalyses were carried out using a Heraeus CHN–O– Rapid analyzer. Melting points were measured on an Electrothermal 9100 apparatus and are uncorrected. IR spectra were recorded on a FT-IR Spectrometer Bruker Tensor 27 in the wavenumber range between 4000 and 400 cm À1 using KBr pellets. Electronic spectra were recorded on a Shimadzu, UV-1650 PC spectrophotometer from solution in DMSO. 2.2. Synthesis 2.2.1. Synthesis of the Schiff base ligand The ligand methyl 2-pyridyl ketone semicarbazone (HL, Scheme 1) was prepared by the condensation of semicarbazide hydrochloride (0.8 g, 7 mmol) with methyl 2-pyridyl ketone 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.04.016 ⇑ Corresponding authors. Tel.: +351 220404576 (L. Cunha-Silva). E-mail addresses: shaabani_b@yahoo.com (B. Shaabani), l.cunha.silva@fc.up.pt (L. Cunha-Silva). Polyhedron 57 (2013) 118–126 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly