Spectrochimica Acta Part A 78 (2011) 601–606 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Electrochemical, catalytic and antimicrobial activity of N-functionalized tetraazamacrocyclic binuclear nickel(II) complexes R. Prabu a , A. Vijayaraj a , R. Suresh a , R. Shenbhagaraman b , V. Kaviyarasan b , V. Narayanan a,∗ a Department of Inorganic Chemistry, School of Chemical Sciences, University of Madras, Guindy Campus, Chennai 600 025, India b Centre for Advanced Studies in Botany, University of Madras, Guindy Campus, Chennai 600 025, India article info Article history: Received 12 May 2010 Received in revised form 11 October 2010 Accepted 29 November 2010 Keywords: Cyclam Binuclear Ni(II) complexes Phosphate hydrolysis Cyclic voltammetry Antimicrobial activity abstract The five binuclear nickel(II) complexes have been synthesized by the Schiff base condensation of 1,8-[bis(3-formyl-2-hydroxy-5-methyl)benzyl]-l,4,8,11-tetraazacyclo-tetradecane (PC) with appropri- ate aliphatic diamines and nickel(II) perchlorate. All the five complexes were characterized by elemental and spectral analysis. The electronic spectra of the complexes show three d–d transition in the range of 550–1055 nm due to 3 A 2g → 3 T 2g (F), 3 A 2g → 3 T 1g (F) and 3 A 2g → 3 T 1g (P). These spin allowed electronic transitions are characteristic of an octahedral Ni 2+ center. Electrochemical studies of the complexes show two irreversible one electron reduction waves at cathodic region. The reduction potential of the com- plexes shifts towards anodically upon increasing the chain length of the macrocyclic ring. All the nickel(II) complexes show two irreversible one electron oxidation waves at anodic region. The oxidation potential of the complexes shift towards anodically upon increasing the chain length of the macrocyclic ring. The catalytic activities of the complexes were observed to be increase with increase the macrocyclic ring size. The observed rate constant values for the catalytic hydrolysis of 4-nitrophenyl phosphate are in the range of 5.85 × 10 -3 to 9.14 × 10 -3 min -1 . All the complexes were screened for antimicrobial activity. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Polyazamacrocyclic ligands have been studied in the last few decades for the complexation of transition and lan- thanide metal ions [1–3]. Among them, cyclam (1,4,8,11- tetraazacyclotetradecane) has been attracted a widespread atten- tion owing to its high affinity for transition metals [4–9]. These complexes have been synthesized by condensation of the appro- priate aldehyde and amine precursors around the metal centres. Synthetic binuclear Ni(II) complexes are important to understand the mutual influences of the two metal centres on the electronic, magnetic and catalytic properties of such bimetallic cores. The presence of additional functional groups on one or more pendant arms has been found to enhance the recognition and complexa- tion properties [10–15]. The grafting of pendant arms has also been used to modulate the solubility of the complexes. In particular, the presence of four secondary amine functions allow unlimited derivatization of the macrocycle [16]. The trans-N,N ′ -disubstituted cyclams are of special interest since they can lead to hexa coordi- nated complexes. When the substituents are coordinating arms, the trans-N,N ′ -diprotected cyclams are also convenient precursors for ∗ Corresponding author. Tel.: +91 44 2230 0488; fax: +91 44 2230 0488. E-mail address: vnnara@yahoo.co.in (V. Narayanan). the synthesis of three-dimensional systems such as cyclam based cryptands [17]. Moreover, synthesis of new Schiff bases and their metal com- plexes are still the aim of many recent investigations and played an important role in the development of coordination chemistry as they readily form stable complexes with most of the transition metals. Compartmental macrocyclic ligands having two pheno- lic oxygens as endogenous bridge have been developed for this purpose because they bind two metal centres in close proxim- ity relevant to the active sites of bimetallic enzymes. Bimetallic macrocyclic complexes represent a helpful tool in the study of metal-metal interactions. Metal complexes with these Schiff bases have numerous applications in the area such as, treatment of cancer [18], MRI contrast agents [19], antibactericide agents [20], antivirus agents [21], fungicide agents [22], catalysis [23] and other biological properties [24,25]. The capability of phenol based binucleating lig- ands to bind two metal centres in close proximity was extensively investigated by Bosnich, Busch and others [26–28]. In the present work, we have synthesized phenol based dis- similar dicompartmental ligands using N,N ′ -disubstituted cyclam. The macrocyclic ring has two compartments, one of the com- partment comprises N 4 O 2 donor atoms and other compartment set comprises N 3 O 2 /N 4 O 2 donor atoms. Electrochemical, cat- alytic and antimicrobial properties of the complexes were discussed. 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.11.029