Europium (III) complexes derived from carboxylic-substituted polychlorotriphenylmethyl radicals Nans Roques a , Sandrine Perruchas a,1 , Daniel Maspoch a,2 , Angela Datcu a , Klaus Wurst b , Jean-Pascal Sutter c , Concepcio ´ Rovira a , Jaume Veciana a, * a Institut de Cie `ncia dels Materials de Barcelona (CSIC), Campus Universitari, 08193 Bellaterra, Catalonia, Spain b Institut fu ¨ r Allgemeine Anorganische und Theoretische Chemie, Universita ¨ t Innsbruck, 6020, Innrain 52 a, Austria c Laboratoire de Chimie de Coordination du CNRS, Universite ´ Paul Sabatier, 205 Route de Narbonne, 31077 Toulouse Cedex 04, France Received 28 November 2006; received in revised form 22 February 2007; accepted 3 March 2007 Available online 21 March 2007 Paper presented in the MAGMANet-ECMM, European Conference on Molecular Magnetism. Abstract Two europium (III) complexes (3 and 4) have been obtained reacting europium (III) nitrate and two polychlorotriphenylmethyl rad- icals properly functionalized with one (PTMMC À , 1) and six (PTMHC 6À , 2) carboxylate groups, respectively. While complex 3 reveals a lamellar polar–apolar separated ion pair structure alternating PTM-based bilayers with nonaaquaeuropium cations ([Eu(H 2 O) 9 ](PTMMC) 3 (PTMMCH) 3 Æ 7H 2 O Æ 6EtOH), complex 4 shows a one-dimensional chain-like structure with formula [Eu 2 (PTMHC)(H 2 O) 13 ] Æ 16H 2 O Æ EtOH. Magnetic properties of both complexes were studied in the 2–300 K range, and show the pres- ence of weak inter-radical antiferromagnetic interactions below 5 K. Ó 2007 Elsevier B.V. All rights reserved. Keywords: PTM radicals; Carboxylates; Europium (III); Molecular magnetism; Separated ion pairs 1. Introduction The design of molecular materials with relevant magnetic properties has been one of the main challenges over the last few decades. Among the different synthetic strategies, many studies in this field have been devoted to the so-called metal– radical approach, which combines open-shell metal ions with pure organic radicals as ligands to enhance the mag- netic interactions in the designed complexes [1]. For such a purpose, different types of organic radicals bearing basic coordination sites together with magnetically active metal ions have been employed so far [2]. Indeed, beside the exten- sively studied family of nitroxide based radicals [3], other organic radicals such as verdazyl derivatives [3k,4], o-qui- none ligands [5], tetracyanoethylene (TCNE) and tetracy- anoquinodimethane (TCNQ) radicals anions [6], and diphenyl carbenes have been used [7,8]. In our group, the work developed over the last five years has allowed the addition of a new type of radical to the list of organic open-shell ligands: the carboxylic- substituted polychlorotriphenylmethyl (PTM) radicals (Chart 1). Several aspects make this family of radicals particularly attractive to build up magnetic molecular materials. First, they present astonishing thermal and chemical stabilities, which arise from the shielding of the radical center by six bulky chlorine atoms. Second, these molecules can be functionalized with different number of coordinating groups (from one to six) at different posi- tions (meta or para) with respect to the central methyl 0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.03.021 * Corresponding author. Tel.: +34 93 5801853; fax: +34 93 5805729. E-mail address: vecianaj@icmab.es (J. Veciana). 1 Present address: Groupe de Chimie du Solide, Laboratoire PMC, CNRS – Ecole Polytechnique, 91128 Palaiseau Cedex, France. 2 Present address: Institut Catala ` de Nanotecnologia, Edifici CM7, Campus Universitari, 08193 Bellaterra, Catalonia, Spain. www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 3861–3869