INTRODUCTION Antipyrine, a pyrazolone, was the first synthetic compound used as an analgesic and antipyretic agent. Other pyrazolones have wider applications in pharmaceuticals, agrochemicals and act as dyes in photography and textile industry 1 . Phenylbu- tazone is another derivative having remarkable activity in various rheumatoid and arthritic conditions 2 . Appropriately substituted pyrazolones have also been used as starting mate- rials to prepare other novel pyranopyrazol-4 and 6-ones 3 . Some complexes of 4-acetylpyrazolone have been men- tioned in a recent literature review 4 . Our continuous interest in the chemistry of pyrazoles and the use of some of its deri- vatives as potential ligands for complexation with transition metals 5 has evoked our interest in exploring further studies. We would now like to report our present work on metal comp- lexes of 4-acetyl-1-aryl-3-methylpyrazole-5-ones and their potential as antibacterial and antifungal agents. EXPERIMENTAL All chemicals were purchased from Fluka/Merck. Solvents were of Analytical grade. Melting points were determined using a Gallenkamp apparatus and are uncorrected. IR spectra were recorded on FT-IR Perkin Elmer-Spectrum BX-II spectro- meter and are reported as ν(cm -1 ). Atomic absorptions were Synthesis and Biological Screening of Heterocyclic Ligands-Pyrazole Derivatives Metal Complexes TASNEEM ULLAH SHEIKH 1,2 , MUHAMMAD NAEEM KHAN 3,* , GHULAM HUSSAIN 4,5 , MUHAMMAD MAKSHOOF ATHAR 4 , MUHAMMAD ASHRAF 6 , FAIZUL HASSAN NASIM 6 , SHAFIA ARSHAD 1 , KARAMAT MAHMOOD 1 and MISBAHUL AIN KHAN 1,4 1 Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur, Pakistan 2 Department of Chemistry, Government College of Education, Afzalpur, Pakistan 3 Applied Chemistry Research Center, PCSIR Laboratories Complex, Lahore, Pakistan 4 Institute of Chemistry, University of the Punjab, Quaid-e-Azam Campus, Lahore, Pakistan 5 Shafi Reso Chem, Ferozepur Road, Lahore, Pakistan 6 Department of Biochemistry and Biotechnology, The Islamia University of Bahawalpur, Bahawalpur, Pakistan *Corresponding author: changwani_1@yahoo.com Received: 8 January 2014; Accepted: 17 September 2014; Published online: 26 December 2014; AJC-16550 The Cu(II), Ni(II) and Zn(II) complexes of 4-acyl-5-pyrazolones along with other novel complexes of 4-acyl-5-pyrazolones with the co- ligand 1,10-phenanthroline were prepared and screened for their antibacterial and antifungal activity. Zinc complexes 11, 12 and 13 showed powerful antifungal activity while some of the nickel complexes 7-10 exhibited effective antibacterial activity against both Gram- positive and Gram-negative bacteria. Keywords: Synthesis, Biological screening, Metal complexes, Pyrazole. recorded on Perkin Elmer Analyst 800. Synergy HT (Bioteck, USA) 96-well plate reader was used for antimicrobial assays. Preparation of ligands Preparation of 4-acetyl-3-methyl-1-phenylpyrazole-5- one (Py) (1) and 4-acetyl-3-methyl-1-p-tolyl-5-one (TPy) (2): The ligands (Py, 1) and (TPy, 2) were prepared by the method reported by Jensen 6 with slight modifications 7 in solvent tetrahydrofuran and were re-crystallized from an acidified methanol-water mixture (1:1). Synthesis of complexes Method (A): Simple metal complexes: Py (1) and TPy (2) of 10 mM each were dissolved in 95 % methanol (25 mL) by warming in separate beakers. Prepared solutions of each ligand were added drop-wise with stirring to a solution of metal (II) chloride (10 mM of metal salt in 50 mL of 95 % methanol) in separate reaction vessel. Complexes precipitated out of solution after few minutes to 2 h of stirring. The precipitates were suction filtered, washed well with aqueous methanol (1:1), dried in air and stored in a desiccator over fused calcium chloride. Method (B): Metal complexes with Co-ligands: Py (1) and TPy (2) of 10 mM each were dissolved in 25 mL of 95 % methanol by warming in separate beakers. Co-ligand (10 mM) was dissolved separately in 95 % methanol (25 mL). Prepared ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY Asian Journal of Chemistry; Vol. 27, No. 1 (2015), 257-260 http://dx.doi.org/10.14233/ajchem.2015.17009