Aryldiazenido ruthenium(II) complexes. Structure and characterization of p-tolyldiazenido ruthenium(II) complexes with pyrazole and imidazole ligands J.G. Małecki ⇑ , I. Gryca, M. Penkala Department of Crystallography, Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40-006 Katowice, Poland article info Article history: Received 7 November 2012 Accepted 4 December 2012 Available online 2 January 2013 Keywords: Ruthenium p-tolyldiazenido complexes Pyrazole Imidazole X-ray Electronic structure Absorption and emission electronic spectra DFT abstract The p-tolyldiazenido ruthenium(II) complexes [RuCl 3 (PPh 3 ) 2 (N 2 PhCH 3 )]CH 3 OH (1), [RuCl 3 (PPh 3 ) (N 2 PhCH 3 )(HPz)] (2) and [RuCl 3 (PPh 3 )(N 2 PhCH 3 )(Im)]CH 3 OH (3) were synthesized and characterized by IR, 1 H, 13 C, 31 P NMR, electronic absorption and emission spectroscopy, and X-ray crystallography. In the molecular structure of complex (1) some p–p stacking interactions are observed, whereas in the structure of the imidazole complex (3) graph set analysis shows intermolecular hydrogen bonded rings. The electronic structures of the complexes were calculated by DFT based on their crystal structures. The spin-allowed singlet–singlet electronic transitions of the complexes were calculated by time-dependent DFT and the UV–Vis spectra have been discussed on this basis. The emission properties of the complexes were also studied. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Research involving ruthenium coordination chemistry incorpo- rating various kinds of ligands has upsurged in recent years due to the fascinating reactivities exhibited by the resultant complexes [1]. Although most of the ligands containing azo nitrogen are multid- entate (bi- or tridentate), the coordination mode of azo nitrogen to transition or non-transition metal ions is well documented [2–14]. Studies on the chemistry of ruthenium complexes with azo ligands have been ongoing and several interesting results related to electron transfer reactions, formation of metal–carbon bonds, aromatic ring amination, isomerism, cytotoxicity toward cancer cells, application in catalytic transformations and complexes with azo ligands that can act as a molecular switch, have been reported [15–23]. A signif- icant property of the azo type ligands, due to the presence of the – N@N– group, is that it may lead to the stabilization of low valent metal oxidation states. This is caused by its p acidity and the presence of low lying azo-centered p / -molecular orbitals [24,25]. However most of the studied complexes containing the R–N@N–R 0 type azo compounds as well as the aryldiazenido com- plexes have been overlooked in the literature. Nevertheless, some papers referred to aryldiazenido complexes of selected metals of groups 17, 18 and 19, i.e. Mn, Re and Ir [26–34]. Several reports on ruthenium aryldiazenido complexes have been released in the 1970s [35–40]. These studies concerned the synthesis and primary spectroscopic characterization (IR, 1 H NMR). Indeed, the Cam- bridge Structural Database (CSD; ConQuest v. 1.14; 2012) presents only one structure of a ruthenium(II) phosphine complex with a p-tolylazo ligand, published in 1973 [41]. Research on p-tolyldiazo complexes, especially ruthenium ones, concern the coordination geometries of the diazo ligand and its similarity to the nitrosyl group. The isoelectronic nature of NO + and the ArN 2 + moiety allows the assumption that the coordinated aryldiazonium cation may also exhibit a duality of bonding modes. It can be characterized as either linear or bent M–N–N structural units, as shown in scheme below: Based on crystallographic evidence, it can be concluded that for describing the linear mode of bonding, the Ib unit is clearly more important than unit Ia. Similar studies extended by the dynamic behavior of aryldiazenido ligands in half sandwich ruthenium(II) complexes have been published in 2000 [42]. Nevertheless the reactivity of ruthenium aryldiazenido com- plexes has not been investigated yet. Moreover their electronic structures, bonding properties as well as absorption and emission electronic spectra have not been determined by density functional 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.12.012 ⇑ Corresponding author. E-mail address: gmalecki@us.edu.pl (J.G. Małecki). Polyhedron 51 (2013) 102–110 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly