Stoichiometric molecular single source precursors to cobalt phosphides Paulin Buchwalter a,b,c , Jacky Rosé b , Bénédicte Lebeau a , Pierre Rabu c,⇑ , Pierre Braunstein b,⇑ , Jean-Louis Paillaud a,⇑ a Equipe Matériaux à Porosité Contrôlée (MPC), Institut de Science des Matériaux de Mulhouse (IS2M), UMR CNRS 7361 – UHA, ENSCMu, 3b rue Alfred Werner, F-68093 Mulhouse Cedex, France b Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS – UdS), 4 rue Blaise Pascal, 67081 Strasbourg Cedex, France c IPCMS-DCMI, UMR 7504 (CNRS, UdS) and NIE, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France article info Article history: Received 12 June 2013 Received in revised form 9 September 2013 Accepted 12 September 2013 Available online 24 September 2013 Keywords: Organometallic clusters Single-source precursors Cobalt phosphides Powder X-ray diffraction Scanning electron microscopy abstract Crystalline cobalt phosphides were synthesized by using three different, low oxidation-state organome- tallic clusters as precursors, [Co 4 (CO) 10 (l-dppa)], [Co 4 (CO) 10 (l 4 -PPh) 2 ] and [Co 4 (CO) 8 (l-dppa) 2 ] (dppa = Ph 2 PNHPPh 2 ), which are characterized by Co/P ratios of 2:1, 2:1 and 1:1, respectively. Depending on their Co/P ratio, these clusters are suitable single-source precursors to form CoP and Co 2 P without the need to add any other reagent or surfactant. The thermal behavior of these three clusters was investi- gated under different conditions. The results show how their Co/P ratios, the nature of the atmosphere used for their thermal activation and the temperature control the nature and composition of the resulting phases. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Metal phosphides have been studied extensively in the past 20 years, largely because they exhibit not only a broad range of physical properties such as magnetism and data storage [1–3], superconductivity [4], magnetocaloric effect [5], magnetoresis- tance [6], optoelectronics or luminescence [7–9], but also interest- ing chemical properties, including lithium intercalation [10,11], improved performances for lithium ion batteries [12,13], or cata- lytic activity [1,14–17]. In particular, metal phosphides have been used as hydrotreatment catalysts for reactions such as hydrodesul- furization (HDS), hydrodenitrogenation (HDN) and hydrodeoxy- genation (HDO). While Ni 2 P exhibits the best activities in both HDS [18] and HDO [16], MoP and WP give the best results in HDN [19,20]. Moreover, CoP is quite active in HDS [21,22], and Co 2 P shows promising results in HDO [16]. Traditionally, metal phosphides have been synthesized by reacting toxic phosphines or phosphorus pentachloride with met- als or metal salts [23,24]. More recently, nanometric phosphides, such as FeP [25], CoP [26], Co 2 P [26,27], Ni 2 P [27–30] and Cu 3 P [27–29] have been obtained by solvothermal methods with a rather large polydispersity. The addition of surfactants to control the size and shape of the nanoparticles (NPs) was introduced later [30]. Dendritic nanostructured Ni 2 P [31], and Co 2 P nanorods [32] were successfully synthesized under such conditions. Brock et al. have obtained MnP, FeP, and CoP nanocrystals [33,34] by using an organometallic route. The reaction of [Mn 2 (CO) 10 ] with P(SiMe 3 ) 3 in trioctylphosphine oxide with an additional surfactant led to stabilized MnP nanospheres of tunable size. Similar ap- proaches led to FeP and CoP NPs. Park et al. developed an original access to a number of transition metal phosphides, by thermal decomposition of a continuously delivered metal–phosphine com- plex to the reacting mixture [35,36]. Reactions of the correspond- ing metal–carbonyl, metal–acetylacetonate or metallocene complex with trioctylphosphine (TOP) resulted in Mn, Fe, Co and Ni metal–phosphine complexes, precursors to MnP, FeP, Co 2 P and Ni 2 P nanorods, respectively. More recently, the formation of metal phosphides was reported where metallic NPs are first formed in situ and then reacted with an adjusted concentration of TOP to form the desired phosphides, through a nanoscale Kirkendall effect (difference of diffusion rate between two types of atoms). Ni 2 P nanocrystals [37] or hollow nanospheres could be synthesized in this manner, as well as a broad range of transition metal phos- phides that were not accessible before, such as PtP 2 , Rh 2 P, Au 2 P 3 , Pd 5 P 2 , and PdP 2 [38]. The same group reported the synthesis of Rh 2 P nanocrystals with various shapes (cubes, triangles, multi- pods) [39] using the same sequence of reactions. Various transition metal phosphides have been prepared using this methodology, not only as nanocrystals, but also as bulk, thin films and foils [40].A detailed investigation of the transition steps from e-Co to Co 2 P, 0020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2013.09.019 ⇑ Corresponding authors. Tel.: +33 3 89 336 884 (J.-L. Paillaud). E-mail addresses: pierre.rabu@ipcms.u-strasbg.fr (P. Rabu), braunstein@ unistra.fr (P. Braunstein), jean-louis.paillaud@uha.fr (J.-L. Paillaud). Inorganica Chimica Acta 409 (2014) 330–341 Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica