Metal Complex of the First-Generation Quinolone Antimicrobial Drug Nalidixic Acid: Structure and Its Biological Evaluation Anamika Debnath & Navin Kumar Mogha & Dhanraj T. Masram Received: 29 May 2014 /Accepted: 14 December 2014 # Springer Science+Business Media New York 2014 Abstract A novel binuclear squire planar complex of nalidixic acid with Ag(I) metal ion with the formula [Ag(Nal) 2 ] has been synthesized. The synthesized metal complex was character- ized using CHN analysis, Fourier-transformed infra-red (FT-IR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), ultra violet–visible (Uv–vis) and single- crystal X-ray diffraction (XRD). The newly synthesized complex shows more advanced antifungal activity compared to the parent quinolone against four fungi, namely Pythium aphanidermatum, Sclerotinia rolfsii, Rhizoctonia solani and Rhizoctonia bataticola. Keywords Quinolone . Nalidixic acid . Metal complex . FT-IR . Single crystal Introduction The coordination chemistry of the metal complexes has developed rapidly due to its versatile applications [1]. Its development in the field of bioinorganic chemistry has also been another important factor in the growth of complexes of macrocyclic compounds [2, 3]. The biological efficacy of certain metal ions draws an attention of many scientists for the synthesis and study of inorganic compounds containing biologically active ligands. Many naturally occurring biomolecules like chlorophyll, haemoglobin, etc. are some evidences for the importance of coordination chemistry [4–10]. Quinolones are one of the bioligands containing 4-oxo-3-carboxylic-1,4- dihydroquinoline skeleton, with bactericidal effect, good oral absorption, excellent bio- availability and good penetration into tissues[11, 12]. Nalidixic acid (Nal) (Fig. 1) is the first member of quinolones [13]. It is a gram-negative microbial agent and is used in the treatment of various infectious diseases like urinary tract infections, soft tissue infections, respiratory infections, bone-joint infections, typhoid fever, sexually transmitted diseases, Appl Biochem Biotechnol DOI 10.1007/s12010-014-1450-9 Electronic supplementary material The online version of this article (doi:10.1007/s12010-014-1450-9) contains supplementary material, which is available to authorized users. A. Debnath : N. K. Mogha : D. T. Masram (*) Department of Chemistry, University of Delhi, Delhi 110007, India e-mail: dhanraj_masram27@rediffmail.com