Unique examples of copper(II)/sodium(I) and nickel(II)/sodium(I) Schiff base complexes with bridging bis-bidentate Salen type ligand: Synthesis, crystal structures and antibacterial studies Niloofar Mahlooji a , Mahdi Behzad a,⇑ , Hadi Amiri Rudbari b , Giuseppe Bruno c , Bahram Ghanbari d a Department of Chemistry, Semnan University, Semnan 35351-19111, Iran b Faculty of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran c Università degli Studi di Messina, Dip. Scienze Chimiche, Viale Ferdinando S. d’Alcontres, 98166 Messina, Italy d Department of Chemistry, Sharif University of Technology, Tehran 11155-3516, Iran article info Article history: Received 8 December 2015 Received in revised form 3 February 2016 Accepted 22 February 2016 Keywords: Heteronuclear Schiff base Bis-bidentate bridging ligand Antibacterial activity abstract Two unique heteronuclear Schiff base complexes of Cu(II), [{Cu(L)Na(ClO 4 )} 2 (l-H 2 L)] (1) and Ni(II), [{Ni (L)Na(BF 4 )} 2 (l-H 2 L)] (2) were synthesized and characterized by different spectroscopic methods as well as X-ray crystallography. The Schiff base ligand (H 2 L) was synthesized from the condensation meso-1,2- diphenyl-1,2-ethylenediamine with 3-methoxysalicylaldehyde. The 3d metal ions in these complexes have been accommodated by the inner N 2 O 2 compartment of the Schiff base ligand, while the O 2 O 0 2 outer compartment has accommodated the Na(I) ion (O and O 0 denote the phenolic and methoxy oxygen atoms, respectively). Besides, a Schiff base ligand has doubly bridged the M(II)/Na(I) moieties via the (OO 0 ) 2 coordination mode. This mode of bidentate action of a potentially tetradentate Schiff base ligand is very rare and has been observed for the first time in such 3d-ns complexes. The in vitro antibacterial activity of the Schiff base ligand and the complexes (1) and (2) were tested against human pathogenic bacteria such as Bacillus subtilis (Gram positive); Staphylococcus aureus (Gram positive); Salmonella typhi (Gram negative); and Escherichia coli (Gram negative). The results showed that these new hetero-polynu- clear complexes had moderate antibacterial activity against both Gram type bacteria. Ó 2016 Published by Elsevier B.V. 1. Introduction The coordination chemistry of alkali metal ions has attracted great interest over the past decades [1]. More recently, bimetallic coordination compounds of 3d-ns metal ions have been the subject of several studies [2,3]. Various compartmental ligands have been used for the synthesis of such 3d-ns heteronuclear complexes [4–6]. The simplest of such ligands are perhaps Salen type Schiff bases derived from 3-methoxysalicylaldehyde (o-vanillin). Their deprotonated forms are fascinating side-off compartmental ligands with two different coordination spheres, which have been used for the synthesis and the study of several multi metallic complexes [6–9]. The inner N 2 O 2 compartment is excellent for accommodat- ing a 3d metal ion, while the larger outer O 2 O 0 2 compartment can bind another metal ion to form a number of 3d-ns, 3d-3d, 3d-4f and 3d-np [2,5,7–13] homo and heteronuclear complexes. The so-obtained bimetallic systems have found particularly impor- tant applications in ionic ferroelectric materials, switchable non- linear optical devices, electro optical devices, biochemistry, etc. [1,14]. Furthermore, such dinuclear Schiff base complexes have shown great structural diversities which have fascinated the researchers in the area of solid state sciences and crystal engineering. Herein, we report the synthesis of two new Cu(II)/Na(I) and Ni (II)/Na(I) Schiff base complexes. The Schiff base ligand (H 2 L) was synthesized from the condensation of 3-methoxysalicylaldehyde with meso-1,2-diphenyl-1,2-ethylenediamine. In the crystal struc- ture of the complexes, the 3d metal ions were placed in the expected inner N 2 O 2 compartment and the alkali metal ion was placed in the outer O 2 O 0 2 compartment. Interestingly, one mole- cule of the Schiff base ligand has doubly bridged the obtained M (II)/Na(I) moieties to form tetranuclear [{M(II)/Na(I)} 2 (l-H 2 L)] complexes; so the potentially tetradentate Schiff base ligand in these complexes has shown both of its tetradentate coordinating ability as well as a very rare bis-bidentate bridging mode of coor- dination [15]. The complexes were characterized by different spec- troscopic methods including X-ray crystallography. EPR spectrum http://dx.doi.org/10.1016/j.ica.2016.02.040 0020-1693/Ó 2016 Published by Elsevier B.V. ⇑ Corresponding author. Tel.: +98 2333383195. E-mail addresses: mbehzad@semnan.ac.ir, mahdibehzad@gmail.com (M. Behzad). Inorganica Chimica Acta 445 (2016) 124–128 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica