Six new palladium(II) mixed ligand complexes of 2-, 3-, 4- monosubstituted derivative of pyridine ring with caffeine moiety: Synthesis, spectroscopic, morphological structures, thermal, antimicrobial and anticancer properties Foziah A. Al-Saif a, ** , Jehan Y. Al-Humaidi a , Dalal N. Binjawhar a , Moamen S. Refat b, c, * a Department of Chemistry, College of Science, Princess Nourah Bint Abdulrahman University, Riyadh,11671, Saudi Arabia b Department of Chemistry, Faculty of Science, Taif University, Al-Haweiah, P.O. Box 888, Zip Code, 21974, Taif, Saudi Arabia c Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt article info Article history: Received 13 April 2020 Received in revised form 26 May 2020 Accepted 26 May 2020 Available online 29 May 2020 Keywords: Nicotinamide Pyridinecarboxylic acids Complexity FTIR XRD Biological activity abstract In the present article, new complexes of mononuclear palladium, formed by the interaction of PdCl 2 with nicotinamide (nta), picolinic acid (pia), and isonicotinic acid (ina) have been isolated in the solid state with 1:2 M ratio affords the new compounds [Pd(nta) 2 (Cl) 2 ](I), [Pd(pia) 2 ](II), and [Pd(ina) 2 ](III). The mixed ligand complexes with caffeine (caf) as a secondary ligand have been synthesized and formulated as [Pd(nta)(caf)(Cl) 2 ](IV), [Pd(pia)(caf)(Cl)] (V), and [Pd(ina)(caf)(Cl)] (VI) with ratio of metal: ligand: ligand is 1:1:1. Structures of these products has been established by elemental analyses, conductivity, FTIR, 1 H NMR and thermal analysis data. The shifts of the n(NeH) amino, n(C]N 1 ) pyridine, n(C]O) carboxylic, and n(C]N 9 ) caffeine stretches have been monitored in order to find out the donor sites of the ligands. According to the experimental data, the six complexes can be characterized in the solid state as mononuclear, with a four-coordinate stereochemistry. SEM, TEM, and XRD analysis determined the characteristics of synthesized nanoparticles. The in vitro antibacterial efficiency of the compounds were evaluated by paper disc diffusion method. Compounds were also screened for their anti-cancer activity against colorectal adenocarcinoma (Caco-2) and breast cancer (Mcf-7) cell lines. This study reveals that [Pd(pia) 2 ] complex has a potent cytotoxic agent against human colorectal adenocarcinoma and breast cancer. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Pyridine ring play a significant role in many biological systems such as nicotinamide (vitamin B3), picolinic acid, nicotinic acid, and isonicotinic acid. Pyridine derivatives are associated with some important biological activities such as anti-tubercular, anthel- mintic, fungicidal, antitumor and antibacterial activity [1 ,2]. The pyridine monocarboxylic acids are simple amphoteric electrolytes of considerable biological interest. Certain of their derivatives show remarkable physiological activity; for example nicotinamide is the pellagra preventative factor of the vitamin B2 complex and iso- nicotinic acid hydrazide is the newly discovered anti-tuberculosis drug [3]. Nicotinamide is known as a component of the coenzyme, nicotinamide adenine dinucleotide (NAD). Nicotinamide itself plays an important role in the metabolism of living cells and some of its metal complexes are biologically active as antibacterial or insulin- mimetic agents [4]. Therefore, the structure of nicotinamide has been the subject of many studies [5,6]. Picolinic acid known as 2-pyridinecarboxylic acid, contains a carboxylic group in the ortho-position to the nitrogen in the pyri- dine ring, acting as a bidentate ligand by (N, COO  ) coordination. It is formed in the body as an intermediate in the triptophan degra- dation pathway and it is also an approved food supplement. In addition, Chromax, is the trade mark name of the Cr(pic) 3 complex, which is currently being used as a food additive and has been * Corresponding author. Department of Chemistry, Faculty of Science, Taif Uni- versity, Al-Haweiah, P.O. Box 888, Zip Code, 21974, Taif, Saudi Arabia. ** Corresponding author. E-mail addresses: faalsaif@pnu.edu.sa (F.A. Al-Saif), msrefat@yahoo.com (M.S. Refat). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc https://doi.org/10.1016/j.molstruc.2020.128547 0022-2860/© 2020 Elsevier B.V. All rights reserved. Journal of Molecular Structure 1218 (2020) 128547