Re(V) complexes formed by metal-assisted solvolysis of di-(2-pyridyl)ketone: Synthesis, X-ray studies, redox behavior and DFT calculations C. Pejo a , H. Pardo b , A. Mombrú b , M.F. Cerdá c , J.S. Gancheff a , R. Chiozzone a , R. González a,⇑ a Cátedra de Química Inorgánica, Departamento ‘‘Estrella Campos’’, Universidad de la República, Av. Gral. Flores 2124, CC 1157, 11800 Montevideo, Uruguay b Laboratorio de Cristalografía, Facultad de Química, Universidad de la República, Av. Gral. Flores 2124, CC 1157, 11800 Montevideo, Uruguay c Laboratorio de Biomateriales, Facultad de Ciencias, Universidad de la República, Iguá 4225, Montevideo, Uruguay article info Article history: Received 1 January 2011 Received in revised form 23 May 2011 Accepted 2 June 2011 Available online 12 June 2011 Keywords: Re(V) complexes Di-2-pyridylketone Crystal structures Electrochemistry DFT and TDDFT calculations abstract The complexes {ReOCl 2 [(py) 2 C(O)(OR)]}, (R = CH 2 CH 3 (1), CH 2 CH 2 CH 3 (2)) were obtained from the metal- assisted alcoholysis reaction of di-2-pyridylketone. Their crystal structures were determined by single- crystal X-ray diffraction. The structures of 1 and 2 consist of neutral mononuclear molecules containing the [ReO] 3+ core. In both compounds the Re(V) central ion is also bonded to an oxygen and both nitrogens from the organic ligand and two chlorides in a distorted octahedral environment. Cyclic voltammograms in CH 3 CN solutions showed two main redox responses, both of them involving one electron transfer. Comparative theoretical studies on equilibrium geometries and electronic properties were conducted in the framework of the density functional theory (DFT). Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The study of the coordination chemistry of rhenium has drawn growing interest in the last 20 years. The potential of using the nu- clear properties of 186 Re (medium energy b-particle emitter, 90 h half-life) and 188 Re (a higher energy b-particle emitter with 17 h half-life) to treat cancerous tumors has long been recognized [1]. Furthermore, the potential applications offered by rhenium com- plexes due to their reactivity and their photophysical properties have also encouraged the developing of rhenium chemistry [2]. The wide coordination chemistry of rhenium comprises several easily accessible oxidation states ranging from +1 to +7. Among them, +5 oxidation state shows very stable compounds character- ized by the presence of stable oxido cores [ReO] 3+ and [O@Re@O] + [3,4], where the bonding with a hard base lowers the high positive formal charge of the metal ion. The coordination sphere can be com- pleted by soft bases like amines [5]. This is the case of di 2-pyridil-ke- tone ((py) 2 CO) which has two pyridinic nitrogens that allow this molecule to act as a didentate N,N 0 -chelate agent. (py) 2 CO has an additional potential coordinating carbonyl oxygen, this ligand being then able to bind to metals in a N,O-coordination fashion [6]. However, (py) 2 CO can undergo solvent nucleophilic addition on the carbonyl group in the presence of metals. When the reaction medium is water the resulting ligand is the gem-diol (py) 2 C(OH) 2 . The corresponding hemiacetal (py) 2 C(OH)(OR) is generally obtained in alcohols (ROH). The deprotonated forms of these molecules are very flexible mononegative tridentate N,O,N 0 -chelating agents that offer multiple coordination possibilities, both as terminal and bridg- ing modes,. The versatility of solvolyzed (py) 2 CO ligands has led to the obtaining of a large number of compounds with different nucle- arities and structure topologies [7–9]. In spite of the copious information regarding the coordination chemistry of (py) 2 CO-based ligands, the one involving rhenium metal is scarce [10]. Hence, in the context of the aforementioned considerations and as part of our interest on contributing to incre- ment basic knowledge on chemical and physical properties of rhenium compounds [11,12], we investigated the behavior of (py) 2 CO towards a Re(IV) compound, namely, NBu 4 [ReCl 5 (DMF)] (DMF = N,N 0 -dimethylformamide). Herein, we report the syntheses of the new compounds {Re- OCl 2 [(py) 2 C(O)(OR)]}, (R = CH 2 CH 3 (1), CH 2 CH 2 CH 3 (2)) afforded by metal-assisted solvolysis of (py) 2 CO. Crystal structure and redox behavior of these Re(V) compounds containing the [ReO] 3+ core are also presented. Comparative theoretical studies on equilibrium geometries and electronic properties were conducted in the frame- work of the density functional theory (DFT). 2. Experimental 2.1. Materials and methods (NBu 4 )[ReCl 5 (DMF)] was prepared following the literature pro- cedure [13]. All the other chemicals and solvents were purchased from commercial sources and used without further purification. 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.06.010 ⇑ Corresponding author. Tel.: +598 2924 9739; fax: +598 2924 1906. E-mail address: rgonzale@fq.edu.uy (R. González). Inorganica Chimica Acta 376 (2011) 105–111 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica