Synthesis of [Fe(hptrz) 3 ](OTs) 2 spin crossover nanoparticles in microemulsion Il’ya A. Gural’skiy a,b , Gábor Molnár a , Igor O. Fritsky b , Lionel Salmon a,⇑ , Azzedine Bousseksou a a Laboratoire de Chimie de Coordination, CNRS UPR-8241 and Université de Toulouse, UPS, INPT, F 31077, Toulouse, France b Department of Chemistry, National Taras Shevchenko University, 62 Vladimirska Str., 01601 Kiev, Ukraine article info Article history: Received 15 December 2011 Accepted 7 March 2012 Available online 17 March 2012 Keywords: Spin crossover Reverse micelles Nanoparticles Iron Triazole abstract Synthesis of the [Fe(hptrz) 3 ](OTs) 2 spin crossover nanoparticle samples was performed. Transmission electronic microscopy was used to determine the size and size distribution of the nanoparticle samples for which a size range of 35–70 nm was found – depending on the composition and the stoichiometry of the reverse micelle hexane-tergitol-water system. The factors susceptible to influence the aggregation degree of the nanoparticles, i.e., the starting experimental conditions, the experiment time and the effect of sonication were also studied. In comparison with the bulk powder sample, these nano-materials still exhibit spin crossover near room temperature with a hysteresis loop. The size-properties relationship concerning the present compound and analogue complexes within this family is also discussed. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Spin crossover (SCO) is one of the most spectacular and well studied phenomena of molecular bistability which can be followed through the change of magnetic, optical and electrical properties of the compound [1]. This phenomenon can be induced by various external stimuli like temperature, pressure, light irradiation, mag- netic field and guest molecules inclusion [2]. It can take place in the case of transition metal ions of electronic configuration 3d 4 – 3d 7 and is mostly studied for Fe(II) complexes. Besides the interest- ing fundamental aspects, potential applications, such as molecular memories, switching devices and sensors continue to draw atten- tion to the spin crossover phenomenon. During the last 5 years much attention has been paid towards the study of SCO nano-objects in order to find size-property corre- lations and also due to the various possible applications through their bistability. Herein we report the synthesis of nanoparticles based upon the [Fe(hptrz) 3 ](OTs) 2 complex using the well known reverse micelles technique [3]. In the present case the formation of the particles happens in the water droplets existing in the tergitol/hexane/water system. The reverse micelle technique implemented in the cited works is a good approach to obtained SCO nanometric particles in solution. This method allows to reach different sizes particles changing the synthetic conditions. How- ever, the separation of nanoparticles from micellar system may be difficult. This method has been already applied for the prepara- tion of nanoparticles of other SCO 1,2,4-triazole complexes [4] as well as for the preparation of nanoparticles based upon Hoffman clathrate 3D coordination polymers [5]. However, it is important to note that the few works previously reported on the synthesis of 1,2,4-triazole complex nanoparticles have brought different and somewhat contradictory information about the size-properties correlations. We have chosen the complex [Fe(hptrz) 3 ](OTs) 2 because of its spin transition taking place just above room temperature [6]. This feature simplifies the study of the properties and can be a useful asset also for potential practical applications. The structure of Fe(II) complexes with 1,2,4-triazoles is known to be generated by iron ions connected by bridging triazole ligands to form 1D-coordina- tion polymer chains (see Scheme 1) [7]. The coordination environ- ment of the metal centers in these compounds and the possible interaction between the chains cause an ability of the iron ions to undergo cooperative spin transition which can occur near room temperature. The aim of this work is to study the properties of novel SCO nano-objects within the family of Fe(II) triazole complexes for a better understanding of the size reduction effects and also to study the factors influencing the mechanism of the formation of the nanoparticles obtained using the reverse micelle method. 2. Experimental 2.1. Material and methods All the chemicals and solvents were obtained from Sigma Aldrich and used without any further purification. Iron(II) tosylate was syn- thesized by reaction between metallic iron and p-toluenesulphonic 0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.poly.2012.03.012 ⇑ Corresponding author. E-mail address: lionel.salmon@lcc-toulouse.fr (L. Salmon). Polyhedron 38 (2012) 245–250 Contents lists available at SciVerse ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly