1,10-Phenanthroline-5,6-dione complexes of middle transition elements: Mono- and dinuclear derivatives Euan K. Brechin a , Lucia Calucci b , Ulli Englert c , Ludovica Margheriti d , Guido Pampaloni d, * , Calogero Pinzino b , Alessandro Prescimone d a School of Chemistry, The University of Edinburgh, West Mains Road, EH9 3JJ Edinburgh, United Kingdom b Istituto per i Processi Chimico-Fisici, CNR, Area della Ricerca, Via G. Moruzzi 1, I-56124 Pisa, Italy c Institut fu ¨ r Anorganische, Chemie der RWTH Aachen, Landoltweg 1, D-52074 Aachen, Germany d Universita ` di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, I-56126 Pisa, Italy Received 20 July 2007; received in revised form 5 December 2007; accepted 8 December 2007 Available online 15 December 2007 Abstract The synthesis and the characterization of several mono- and dinuclear middle transition metal derivatives of 1,10-phenanthroline- 5,6-dione, 1, are presented. The reaction of 1 with CrCl 2 (THF) 2 gives CrCl 2 (O,O 0 -C 12 H 6 N 2 O 2 )(THF) 2 , 2, while the halides of iron(II), cobalt(II) and nickel(II) afford adducts of general formula MX 2 (N,N 0 -C 12 H 6 N 2 O 2 ), M = Fe, 4, Co, 5, X = Cl; M = Ni, 6, X = Br. DFT calculations on CrCl 2 (L)(THF) 2 with L = O,O 0 -C 12 H 6 N 2 O 2 or O,O 0 -C 14 H 8 O 2 allowed a direct comparison of the coordination proper- ties of 9,10-phenanthrenequinone and 1,10-phenanthroline-5,6-dione to be made.Dinuclear compoundsof generalformula CrCl 2 (THF) 2 (O,O 0 -C 12 H 6 N 2 O 2 -N,N 0 )MX n L m , M = Zr, 7, X = Cl, n = 4, m = 0;M = Cr, 8, X = Cl, n = 2, L = THF, m = 2; M = Fe, 9, Co, 10, X = Cl, n = 2, m = 0; M = Ni, 11, X = Br, n = 2, m = 0, are prepared from 2 and the corresponding meta while VCp 2 (O,O 0 -C 12 H 6 N 2 O 2 -N,N 0 )FeCl 2 , 12,is synthesized by reacting 4 with VCp 2 . The electronic properties of the different com- plexes are investigated by magnetic moment measurements and EPR spectroscopy. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Chromium; Iron; Cobalt; Nickel; 1,10-Phenanthroline-5,6-dione; 9,10-Phenanthrenequinone; EPR spectroscopy; DFT calculations 1. Introduction Studies have dealt with the coordination properties of 1,10-phenanthroline-5,6-dione, 1, towards both early and late transition metals and lanthanides [1]. The versatile behaviour of1 is exemplified by its reaction with TiCl 4 or TiCp 2 (CO) 2 , wherethe changein the coordination environmentaround titanium allows the isolation of O,O 0 - or N,N 0 -coordinated compounds, see Scheme1 [1e,g]. It has to be noted that complexes of type I may be used as ‘‘quinone equivalent” ligands in reactions with compoundscontaining metals in a low oxidation state, and the oxygen-bound complexes of 1,10-phenanthro- line-5,6-dione, type II, may be used as‘‘phenanthroline equivalent” ligands in reactions with Lewis acids. In both cases,the resultis the formation ofcomplexes of higher nuclearity. In this paper, we report on the preparation of some new chromium,iron, cobaltand nickelcomplexes containing N,N 0 - or O,O 0 -coordinated 1, which have also been used to grow homo- or hetero-dinuclear compounds containing 1 as bridging ligand. Moreover, a comparative study of th coordination properties of 1 and 9,10-phenanthrenequi- none has been performed based on the magnetic momen measurement and DFT calculations on CrCl 2 (L)(THF) 2 , with L = O,O 0 -C 12 H 6 N 2 O 2 and O,O 0 -C 14 H 8 O 2 . 0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.12.011 * Corresponding author. Tel.: +39 050 2219 219; fax: +39 050 2219 246. E-mail address: pampa@dcci.unipi.it (G. Pampaloni). www.elsevier.com/locate/ica Available online at www.sciencedirect.com Inorganica Chimica Acta 361 (2008) 2375–2384