Synthesis, structure, spectroscopic properties, electrochemistry, and DFT correlative studies of trans-[Ru(P-P) 2 Cl 2 ] complexes Mousa Al-Noaimi a,⇑ , Ismail Warad b,⇑ , Obadah S. Abdel-Rahman c , Firas F. Awwadi d , Salim F. Haddad d , Taibi B. Hadda e a Department of Chemistry, Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan b Department of Chemistry, AN-Najah National University, Nablus, Occupied Palestinian Territory c Fachbereich Chemie der Universität Konstanz, Universitätstraße 10, D-78457 Konstanz, Germany d Chemistry Department, Faculty of Science, The University of Jordan, Amman 11942, Jordan e Laboratoire LCM, Faculty of Sciences, University Mohammed 1er, Oujda 60000, Morocco article info Article history: Received 22 April 2013 Accepted 16 June 2013 Available online 27 June 2013 Keywords: Ruthenium Diphosphine Electrochemistry DFT calculation abstract Five trans-[Ru(P-P) 2 Cl 2 ] complexes were prepared by reacting RuCl 2 (PPh 3 ) 3 with P-P ligands {P-P = 3-hexyl-1,3-bis(diphenylphosphino)propane (hdppp) (1); = 1,3-bis(diphenylphosphino)propane (dppp) (2); = 1,2-bis(diphenylphosphino)ethane (dppe) (3); 1.1 0 -bis(diphenylphosphino)methane (dppm) (4); 1,2-bis(diphenylphosphino)ethylene (depe) (5)}. The complexes were characterized by an elemental analysis, IR, 1 H, 13 C and 31 P{1H}NMR, FAB-MS and TG/DTA. These Ru(II) complexes showed Ru(III)/Ru(II) quasireversible redox couple. The molecular structures of the complexes 1 and 3 were determined by X-ray crystallography, and their spectroscopic properties were studied. Another poly- morph of 3 was reported in literature, the reported polymorph of 3 in this work crystallizes in P  1 space group, whereas, the previously reported polymorph crystallizes in C2/c space group. The two complexes adopt a distorted trans octahedral coordination and ruthenium(II) ions are located on a crystallographic centre of symmetry. Based on the optimized structures, computational investigations were carried out in order to determine the electronic structures of the complexes. The electronic spectra of 1 and 1 + in dichloromethane were calculated with the use of time-dependent DFT methods, and the electronic spec- tra of the transitions were correlated with the molecular orbitals of the complexes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Ruthenium(II) complexes with polydentade phosphines ligands have received much attention in the last decades due to their application in the field of homogeneous catalysis [1,2]. Several complexes of the general formula cis- and trans-[M(P-P) 2 X 2 ] (P-P = C 2 H 4 (PR 2 ) 2 (R = Me, Et or Ph), CH 2 (PPh 2 ) 2 , and o-C 6 H 4 (PEt 2 ) 2 ; X = halogen, SCN 1 ,H 1 , CN 1 ) (M = Ru, Os) were prepared by Chatt and Hayter [3,4]. These complexes, trans-[Ru(P-P) 2 Cl 2 ], could be used as starting materials to prepare bi- and pronuclear com- plexes [5,6]. Classical procedures for the syntheses of these com- plexes require the reflux conditions in acidic media [7] or the aqueous solution of K 2 [RuCl 5 (H 2 O)] [8]. Poor yields of complexes are obtained by these preparation procedures. For this reason, a study of the electronic structures of such complexes is valuable as a mean to predict their properties [9–11]. In this paper, we present the synthesis, crystal, molecular, the electronic structures, and the spectroscopic characterization of five ruthenium(II) complexes with diphosphine ligands. The trans-[Ru(P-P) 2 Cl 2 ] complexes, (P-P) {P-P = (Hdppp) = 3-hexyl-1,3- bis(diphenylphosphino)propane (1); (dppp) = 1,3-bis(diphenyl- phosphino)propane (2); (dppe) = 1,2-bis(diphenylphosphino)eth- ane (3) (dppe); (dppm) 1.1 0 -bis(diphenylphosphino)methane (4); 1,2-bis(diphenylphosphino)ethylene (5)}, were prepared from the reaction RuCl 2 (PPh 3 ) 3 and the corresponding P-P ligand. These trans complexes have a poor solubility in many organic solvents. The solubility can be improved by modification of the diphospine backbone chelating ligand with alkyl group. Hdppp is a newly pre- pared diphosphine ligand to improve the solubility of the trans- [Ru(P-P)Cl 2 ] complexes. To probe the effect of the size of chelating ring of P-P on the electronic behavior trans-[RuCl 2 (P-P) 2 ] com- plexes. In this work, we present and discuss the spectroscopic (IR, UV–Vis, 1 HNMR and 31 PNMR) and electrochemical (cyclic vol- tammetry) behavior of 1–5, and report the X-ray structures for 1 and 3. The absorption spectrum of complex 1 and 1 + in dichloro- methane have been modeled by time-dependent density func- tional theory (TD-DFT) using a mixed basis set, MWB/6-31+g(d,p) to correlate experimental findings with theoretical predictions. 0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2013.06.024 ⇑ Corresponding authors. E-mail address: manoaimi@hu.edu.jo (M. Al-Noaimi). Polyhedron 62 (2013) 110–119 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly