Tuning magnetic exchange using the versatile azide ligand Guillaume Chastanet a,b, * , Boris Le Guennic b , Christophe Aronica a,b , Guillaume Pilet a , Dominique Luneau a , Marie-Laure Bonnet b , Vincent Robert b a Laboratoire des Multimatériaux et Interfaces (UMR 5615) CNRS, Université Claude Bernard Lyon 1, Campus de la Doua, 69622 Villeurbanne Cedex, France b Laboratoire de Chimie (UMR 5182), Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France article info Article history: Received 13 February 2008 Accepted 27 February 2008 Available online 4 March 2008 This paper is dedicated to Dante Gatteschi for his great contribution to science and the wonderful time spent in his laboratory. Keywords: Coordination chains 3D metal ions Azide Magnetic properties X-ray structures Ab initio calculations abstract The ability of the azido ligand to generate various chemical architectures and magnetic couplings is sur- veyed, using Cu(II) and Ni(II) derivatives. Depending on the ratio between the azide salt, the metal salt and the tridentate Schiff base LH (L  :1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2- onato), molecular bimetallic [CuL(l 1,3 -N 3 )] 2 (1) and monometallic [NiL(l 1 -N 3 )] (2) as well as extended {[CuL(l 1,1 -N 3 )]} n (3) and {[Ni 2 (l 1,1 -N 3 )(l 1,3 -N 3 )(L) 2 (MeOH) 2 ]} n (4) chains were obtained. These systems were fully characterized by X-ray diffraction and magnetic susceptibility measurements. In 1, the asym- metrical double l 1,3 -N 3 bridge mediates a ferromagnetic exchange whereas 3 and 4 exhibit unusual sym- metric and asymmetric single l 1,1 -N 3 coordination modes that transmit weak ferromagnetic interactions. Ab initio calculations were systematically performed to clarify the origin of the observed magnetic exchanges and to study the role of the asymmetric coordination modes on the magnetic coupling. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The development of new functional molecular-based materials associated with the miniaturization of electronic devices has led to tremendous progresses in low-dimensional systems, in both chemistry and physics communities [1,2]. One of the main chal- lenges in the synthesis of such systems is to prevent the local mag- netic moments from cancelling out. Obviously, this condition is fulfilled as soon as ferromagnetic interactions dominate. However, in the presence of most frequent antiferromagnetic interactions, different strategies have been developed. Especially in the case of 1D systems, pioneer approaches were devoted to regular hetero- spin ferrimagnetic chains [2] holding alternating spin carriers, cou- pled through a unique exchange interaction. Another strategy has consisted in varying the magnetic exchange constants between homospin carriers [3]. Finally, the use of strong anisotropic metal ions has generated the promising field of the single-chain magnets (SCMs) [4]. Pseudo-halide anions are known to be excellent ligands to ob- tain materials with several structures’ dimensionalities. Among these, the azido ligand turned out to be extremely versatile in link- ing metals and a remarkable magnetic coupler for propagating interactions between paramagnetic ions [5,6]. The structural vari- ety of the azido-complexes ranges from molecular clusters [6] to extended 1D [5,7], 2D [8] and 3D [9] materials. The versatility of the N 3  ligand arises from the different coordination modes it can offer. The most encountered are the end-to-end (l 1,3 -N 3 , EE) and end-on (l 1,1 -N 3 , EO) modes (Scheme 1)[5] whereas triply l 1,1,1 [10], l 1,1,3 [11], or quadruply l 1,1,1,1 [12], l 1,1,3,3 [13] modes re- main relatively rare. An additional interesting feature stands in the number of azide ions involved in the coordination of the metal cen- tres. One, two or three azides can be encountered, both for the EE and EO modes, two bridges being the most common coordination [5]. Furthermore, different bridging modes of the azide ions may simultaneously exist in the same species, leading to original alter- nating topologies and magnetic behaviours exemplified by the widespread {EO-EE} n sequence [5,7] and the less common, {EO-EE-EE} n ,{EO-EO-EO-EE} n ,{EO-EO-EO-EO-EE} n chain assem- blies [14]. Concerning the magnetism, the sign and amplitude of the mag- netic exchange may be tuned by differences in the bonding and symmetry modes of the azido-bridge. Several magnetostructural and theoretical studies have evidenced general trends: the EE mode favours antiferromagnetic interaction whereas the EO one leads to ferromagnetic behaviour [5,15,16]. These studies have also 0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2008.02.045 * Corresponding author. Address: Laboratoire des Multimatériaux et Interfaces (UMR 5615) CNRS, Université Claude Bernard Lyon 1, Campus de la Doua, 69622 Villeurbanne Cedex, France. Tel.: +33 (0)4 72 72 88 55. E-mail address: guillaume.chastanet@univ-lyon1.fr (G. Chastanet). Inorganica Chimica Acta 361 (2008) 3847–3855 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica