Synthesis, structural, DFT studies and antibacterial evaluation of Cp / rhodium and Cp / iridium complexes using hydrazide based dipyridyl ketone ligand A. Basava Punna Rao a , Narasinga Rao Palepu a , Debojit Kumar Deb a , A. Uma b , T. Chiranjeevi b , Biplab Sarkar a , Werner Kaminsky c , Kollipara Mohan Rao a,⇑ a Centre for Advanced Studies in Chemistry, North-Eastern Hill University, Shillong 793 022, India b Centre for Biotechnology, IST, JNTU, Kukatpally 500 085, India c Department of Chemistry, University of Washington, Seattle, WA 98195, USA article info Article history: Received 2 December 2015 Received in revised form 26 December 2015 Accepted 28 December 2015 Available online 4 January 2016 Keywords: Half-sandwich complexes Rhodium Iridium Antibacterial DFT abstract The synthesis, characterization and antibacterial evaluation of four new water soluble half-sandwich complexes of N 0 -{di(pyridin-2-yl)methylene}picolinohydrazide (PHADPK-L1) and N 0 -{di(pyridin-2-yl) methylene}nicotinohydrazide (NHADPK-L2) have been described with the general formula [Cp / MLCl] BF 4 where L = L1, M = Rh (1), Ir (2); L = L2, M = Rh (3), Ir (4) have been described. All the complexes have been characterized by elemental analysis and spectral studies. Crystal structures of all the complexes 1–4 have been determined by single crystal X-ray analyses. Preliminary in vitro antibacterial activity of the four complexes was investigated against Gram-positive bacterium Staphylococcus aureus, and Gram- negative bacteria viz., Escherichia coli, Klebsiella pneumonia and Pseuedomonas aeruginosa by agar well dif- fusion method. Spectral and structural studies revealed that the formation of mononuclear complexes takes place by dipyridyl mediated N–N binding. All the complexes exhibited a HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) energy gap from 3.65 to 3.97 eV. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Water-soluble organometallic complexes are attracting an incessant growth in the applicative fields of chemistry like cataly- sis, nanoparticles, nanocages and biological applications like antimicrobial and anticancer studies due to its eco-friendly pro- cessing, isolation of compound and substitution of chloride leaving groups by water [1–6]. Platinum and non-platinum based drugs particularly cisplatin and its analogs are highly active against var- ious tumors [7,8]. An important class of non-platinum chemother- apeutic agents such as NAMI-A, KP1019, KP1339 and RAPTA-C are in clinical trials among them NAMI-A and KP1339 are currently in phase-II clinical trials and RAPTA-C is on its way to progressing clinical trials [9–15]. The RAPTA complexes developed by Dyson and co-workers are known to have selective activity on metastatic tumors in vitro and in vivo similar to that of NAMI-A. Pertaining to rhodium chemotherapeutic agents paddlewheel compounds of dir- hodium and its derivatives are showing good antitumor activity out of that [Rh 2 (O 2 CCH 3 ) 4 ] compound exhibiting antitumor activity against various cell lines [16–21]. Dunbar et al. have found that the rhodium complexes can bind to DNA bases and induce the change of hydrogen bonding environment which is monitored by NMR studies. A property like changing of hydrogen bonding plays a piv- otal role in the in vivo properties of the molecules [22,23]. Iridium is a congener of rhodium, though iridium metal pharmaceuticals are still in their infancy. More recently, Sadler and co-workers found that half sandwich iridium complexes which are functioned as catalytic drugs are potent for the cancer cells, due to their ligand exchange reactions (even in seconds), DNA binding and attack on coenzyme NAD(P)H [24,25]. Many organometallic complexes are focusing on anticancer and antimalarial properties; so far Salvarsan is an anti-infective drug from organometallic compounds [26]. Thus, in view of the above facts and in continuation to our earlier interest [27] on rhodium (III) and iridium(III) complexes, we found it is worthwhile to syn- thesize new mononuclear rhodium(III) and iridium(III) complexes containing picolinic and nicotinic hydrazide derivatives of dipyri- dyl ketone as co-ligands for spectroscopic and antibacterial studies. Herein, we report the synthesis, structural studies accompany- ing density functional theory (DFT) and antibacterial evaluation of http://dx.doi.org/10.1016/j.ica.2015.12.035 0020-1693/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +91 364 272 26260; fax: +91 364 2550076. E-mail address: mohanrao59@gmail.com (K.M. Rao). Inorganica Chimica Acta 443 (2016) 126–135 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica