Mononuclear copper(II) complexes with a tetradentate pyrazole based ligand: Syntheses, structures, DNA binding study and antimicrobial activity Ankita Solanki a , Sujit Baran Kumar a,⇑ , Ankita A. Doshi b , C. Ratna Prabha b a Department of Chemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390 002, India b Department of Biochemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390 002, India article info Article history: Received 1 May 2013 Accepted 17 June 2013 Available online 9 July 2013 Keywords: Tetradentate Pseudohalides Copper(II) complexes Structure DNA binding Antibacterial activity abstract A new tetradentate N 4 -coordinate ligand, N,N-diethyl-N 0 ,N 0 -bis((3,5-dimethyl-1H-pyrazol-1- yl)methyl)ethane-1,2-diamine (dbdmp), and its mononuclear copper(II) complexes [Cu(X)(dbdmp)]Y, where X = N 3  , NCS  , NCO  and Y = ClO 4  , PF 6  and BF 4  , have been synthesized and characterized by microanalysis, physico-chemical and spectroscopic methods. The crystal structures of the four complexes [Cu(N 3 )(dbdmp)]ClO 4 (1) [Cu(NCS)(dbdmp)]ClO 4 (4), [Cu(NCS)(dbdmp)]PF 6 (5) and [Cu(NCO)(dbdmp)]ClO 4 (7) were solved by single crystal X-ray diffraction studies and showed that all the complexes have distorted trigonal bipyramidal geometries. Interaction of CT-DNA with complexes 1–6 were examined by spectroscopic titration and fluorescence techniques and showed that the com- plexes have strong interactions with CT-DNA. The antimicrobial activities of complexes 1–6 were studied by the dilution method against Gram positive (Bacillus subtilis) and Gram negative (Escherichia coli) strains and showed the complete inhibition of the tested strains by the complexes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The synthesis, characterization and structures of transition me- tal complexes and their interactions with DNA have attracted much attention amongst researchers for the potential application in bioinorganic chemistry [1–6]. Transition metal complexes have been widely used for this purpose because of their flexible coordi- nation behavior, different structural and electronic properties, and they bind with DNA by cleaving metal–ligand bonds or by chang- ing the coordination environment [7,8]. Although there are many reports on the interactions of DNA and transition metal complexes [9–22], the interactions of DNA and copper(II) complexes are very interesting because copper is an essential trace element bound to many proteins and enzymes [23–25]. Recently, copper(II) com- plexes with N-donor ligands have shown numerous biological activities, such as antitumor and antibacterial. There are many re- ports on CT-DNA binding studies of copper(II) complexes with nitrogen containing ligands, including polypyridine [26,27]. Metal complexes generally bind to DNA via covalent and non- covalent interactions. In covalent binding, the labile ligand of the complexes interacts with a nitrogen base of DNA. The non-covalent DNA interactions modes are intercalation, electrostatic and groove binding of the cationic metal complexes along the outside of the DNA helix, and are of considerable interest. In most of the interac- tions of DNA with copper(II) complexes investigated so far, the li- gands are either bi- or tridentate nitrogen containing ligands. Investigations on the DNA binding of copper(II) complexes with pseudohalides and tetradentate N 4 -coordinating pyrazole based li- gands are scarce. We have been working on the syntheses, characterization and structures of mono- and binuclear complexes with 3d-transi- tion elements and a pyrazole based ligand [28–31]. In this paper, we report on the syntheses and structural characterizations of the new ligand N,N-diethyl-N 0 ,N 0 -bis((3,5-dimethyl-1H-pyrazol-1- yl)methyl)ethane-1,2-diamine (dbdmp) and its mononuclear cop- per(II) complexes [Cu(X)(dbdmp)]Y, where X = NCS  /N 3  /NCO  ; Y = ClO 4  /PF 6  /BF 4  . The DNA binding and antimicrobial activities of the copper complexes have been discussed. 2. Experimental 2.1. Materials The chemicals and solvents were of analytical grade and pur- chased from commercial sources. Acetylacetone, paraformalde- hyde, hydrazine hydrate, sodium azide, Cu(CH 3 COO) 2 H 2 O (Qualigens, India), N,N-diethylethylenediamine, NH 4 PF 6 , NH 4 BF 4 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.06.051 ⇑ Corresponding author. E-mail addresses: sujit_baran@yahoo.com, kumarsujitbaran@gmail.com (S.B. Kumar). Polyhedron 63 (2013) 147–155 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly