Spectrochimica Acta Part A 76 (2010) 376–383 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Spectroscopic characterization and biological activity of Zn(II), Cd(II), Sn(II) and Pb(II) complexes with Schiff base derived from pyrrole-2-carboxaldehyde and 2-amino phenol Bibhesh K. Singh a,∗ , Anant Prakash a , Hemant K. Rajour b , Narendar Bhojak c , Devjani Adhikari a a Inorganic & Bioinorganic Research Lab, Department of Chemistry, Govt. Post Graduate College, Ranikhet 263645, Uttarakhand, India b Department of Chemistry, Ramjas College, University of Delhi, Delhi 110007, India c Department of Chemistry, Govt. Dunger College, MGS University, Bikaner, India article info Article history: Received 8 January 2010 Received in revised form 15 March 2010 Accepted 17 March 2010 Keywords: Biological activities Spectra Schiff base Metal complexes Molecular modeling Thermal studies abstract A new Schiff base 2-aminophenol-pyrrole-2-carboxaldehyde and its Zn(II), Cd(II), Sn(II) and Pb(II) com- plexes have been synthesized and characterized by various physicochemical studies. Spectral studies (IR and 1 H NMR) indicate deprotonation and coordination of phenolic oxygen along with binding of pyr- role nitrogen, azomethine nitrogen and anion with metal ions. The presence of lattice water molecule(s) has also been confirmed by TG/DTA studies. Mass spectrum explains the successive degradation of the molecular species in solution and justifies ML complexes. Kinetic and thermodynamic parameters were computed from the thermal data using Coats and Redfern method, which confirm first order kinetics. The bio-efficacy of the ligand and their complexes has been examined against the growth of bacteria in vitro to evaluate their antimicrobial potential. Molecular structures of the complexes have been optimized by MM2 calculations and suggest a tetrahedral geometry around metal ions. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Schiff base ligands are considered “privileged ligands” because they are easily prepared by the condensation between aldehydes and amines. Stereogenic centers or other elements of chirality can be introduced in the synthetic design. Schiff base ligand is able to coordinate many different metals [1], and to stabilize them in var- ious oxidation states. Structure–activity relationship of Schiff base compounds are studied due to their antitumor, antimicrobial and antiviral activities [2]. In recent years, because of new interesting applications found in the field of pesticides and medicine, the metal complexes with tridentate O, N, N types of alternative structures have attracted the attention of chemist. Various metal complexes with bi- and tridentate Schiff bases containing nitrogen and oxygen donor atoms play important role in biological system and represent interesting models for metalloenzymes, which efficiently catalyze the reduction of dinitrogen and dioxygen [3]. Schiff base com- plexes incorporating phenolic group as chelating moieties in the ligand are considered as models for executing important biologi- cal reactions and mimic the catalytic activities of metalloenzymes ∗ Corresponding author. Tel.: +91 9760014796; fax: +91 5966220372. E-mail address: bibheshksingh@yahoo.co.in (B.K. Singh). [4]. Furthermore, macrocyclic derivatives of these Schiff bases have many fundamental biological functions, such as photosynthesis and transport of oxygen in mammalian and other respiratory system [5]. In recent years metal compounds, which have a stable d 10 elec- tronic configuration, have received a lot of attention in the fields of inorganic chemistry, biochemistry and environmental chemistry. About twenty zinc enzymes are known in which zinc is generally tetrahedrally four coordinate and bonded to hard donor atoms such as nitrogen [6]. Previously, it has been reported that zinc(II) and cadmium(II) complexes with Schiff bases type chelating ligand can be used as an effective emitting layer and showed photo physical properties [7]. Zinc complexes have been shown to be active as antitumor, anti-HIV and antimicrobial agents [8]. So, our interest is to establish spectroscopic bioactive model complexes of newly synthesized Schiff base with metal ions having d 10 configuration. The present report deals with the synthesis, spectroscopic and thermal characterization of zinc(II), cadmium(II), tin(II) and lead(II) complexes with Schiff base derived from pyrrole- 2-carboxaldehyde and 2-amino phenol and to examine their bio-efficacy of ligand as well as metal complexes. The free ligand and its complexes have been tested in vitro against Escherichia coli and Staphylococcus aureus bacteria with different concentrations, in order to assess their antimicrobial potential. 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.03.031