New formamidine ligands and their mixed ligand palladium(II) oxalate complexes: Synthesis, characterization, DFT calculations and in vitro cytotoxicity Ahmed A. Soliman a,⇑ , Othman I. Alajrawy a,b , Fawzy A. Attabi a , Mohamed R. Shaaban a,c , W. Linert d a Department of Chemistry, Faculty of Science, Cairo University, 12613 Giza, Egypt b College of Veterinary Medicine, Al-Anbar University, Fallujah, Iraq c Department of Chemistry, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia d Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163-AC, A-1060 Vienna, Austria highlights  New formamidine ligands were synthesized and characterized.  Their mixed oxalate Pd(II) complexes were also synthesized and characterized.  The structures are geometrically optimized and the computed vibrations and transition are compared with the experimental.  The cytotoxicity of the ligands and complexes were tested with promising IC 50 values. graphical abstract A series of new ternary palladium(II) complexes of the type [Pd(L 1–4 )ox]xH 2 O where L = formamidine ligands and ox = oxalate, were synthesized and characterized by elemental analyses, magnetic suscepti- bility, UV–Vis, infrared (IR) and mass spectroscopy and thermal analysis. The spectroscopic data indicated that the formamidine ligands act as bidentate N2 donors and the oxalate as O2 ligand. Complex (1) HOMO-Molecular Orbitals Complex (1) LUMO- Molecular Orbitals -0.2346 a.u -0.133 a.u HOMO LUMO E=0.101 article info Article history: Received 17 April 2015 Received in revised form 19 June 2015 Accepted 16 July 2015 Available online 17 July 2015 Keywords: Ternary Pd(II) complexes Oxalate Formamidine Antitumor complexes abstract A series of new ternary palladium(II) complexes of the type [Pd(L 1–4 )ox]xH 2 O where L = formamidine ligands and ox = oxalate, were synthesized and characterized by elemental analyses, magnetic suscepti- bility, UV–Vis, infrared (IR) and mass spectroscopy and thermal analysis. The spectroscopic data indicated that the formamidine ligands act as bidentate N2 donors and the oxalate as O2 ligand. The complexes (1–4) are diamagnetic and the optimization of their structures indicated that the geometry is distorted square planer with O–Pd–O and N–Pd–N bond angles ranged 82.70–83.87° and 88.21–95.02°; respec- tively which is acceptable for the heteroleptic complexes. The dipole moment of the complexes (13.97–18.77 Debye) indicating that the complexes are more polarized than the ligands (1.93– 4.96 Debye). The complexes are thermally stable as shown from their relatively higher overall activation energies (441–688 kJ mol 1 ). The ligands and the complexes are proved to have good cytotoxicity with IC 50 (lM) in the range of (0.011–0.168) against MCF-7, (0.012–0.150) against HCT-116, (0.042–0.094) against PC-3 and (0.006–0.222) against HepG-2 cell lines, which open the field for further application as antitumor compounds. Ó 2015 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2015.07.076 1386-1425/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: ahmedsoliman61@gmail.com (A.A. Soliman). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 152 (2016) 358–369 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa