UNCORRECTED PROOF In situ time-resolved X-ray diffraction study of manganese trifluoride thermal decomposition J.V. Rau a,* , V. Rossi Albertini b , N.S. Chilingarov a , S. Colonna b , U. Anselmi Tamburini c a Chemistry Department, M.V. Lomonosov Moscow State University, 119899 Moscow, Russia b Istituto di Struttura della Materia/CNR, Via del Fosso del Cavaliere, 100-00133 Rome, Italy c Dipartimento di Chimica Fisica, Universita’ di Pavia, Viale Tramelli, 16-27100 Pavia, Italy Received 25 October 2000; accepted 14 February 2001 Abstract The first in situ time-resolved X-ray diffraction study of MnF 3 crystal structure evolution during its thermal decomposition was performed on the GILDA beam line at the European Synchrotron Radiation Facility (ESRF, France). Mn 2 F 5 (s) was observed as intermediate phase during the process of decomposition of MnF 3 (s) to MnF 2 (s). # 2001 Published by Elsevier Science B.V. Keywords: In situ X-ray diffraction; Thermal decomposition; Manganese fluorides 1. Introduction High valency metal fluorides (MnF 3 , CoF 3 , TbF 4 , etc.) are interesting both from theoretical and from practical points of view. They are widely used as fluorinating agents in the synthesis of fluorinated derivatives of organic compounds [1] and are recently found to be promising fluorinating agents in synthesis of gaseous fluorides of transition metals in unusually high oxidation states [2]. Their thermal decom- position leads to the formation of the corresponding lower valency metal fluorides and the release of fluorine [3,4]. Although this is generally assumed to be a simple process, no deeper inspection has been done on the real mechanism hitherto. However, on the basis of mass spectrometric investigations, complex transformations were hypothesised for high valency metal fluorides decomposition [4,5]. The purpose of this work was to study in situ the evolution of the solid phase from MnF 3 to MnF 2 by time-resolved X- ray powder diffraction recorded during thermal transforma- tion. 2. Experimental A Ni capillary, previously passivated by keeping it for 48 h at high temperature (4008C) in a fluorine atmosphere (P ¼ 1 atm), was used as the sample holder. On one hand, the sample holder has to be inert with respect to fluorine; on the other, it has to endure high temperatures (>5008C). Due to the latter constraint, a plastic container could not be used, although a metal capillary has the drawback of being rather opaque to X-rays. This applies to our Ni capillary, despite that the thickness of its walls was only 100 mm. To reduce this effect and, simultaneously, to decrease the intensity of the higher harmonics present in the X-ray beam [6], high energy radiation (24 keV) was utilised. The diffraction measurements were performed on the GILDA beam line at the European Synchrotron Radiation Facility (Grenoble, France). The beam line monochromator was equipped with two Si(3 1 1) crystals, the first is flat, whereas the second is curved to focus the X-ray beam in the horizontal plane. A further reduction of the higher harmo- nics was obtained by a partial de-tuning of the monochro- mator. The calibration of the radiation energy was made by collecting the diffraction pattern of a standard LaB 6 powder [7]. The capillary (6 cm in length) containing the sample was mounted on a rotating system and connected to a pipe supplying an Ar flow during heating. The major problem in the preliminary measurements was connected to the use of the small volume closed capillary. Usually measurements, like gas phase IR spectroscopy or high temperature mass spectrometry, on thermal decomposition of this class of compounds are carried out under vacuum, so that fluorine developed during the decomposition is pumped away. In a Journal of Fluorine Chemistry 4506 (2001) 1–4 * Corresponding author. Fax: þ7-95-939-1240. E-mail address: jrau@phys.chem.msu.ru (J.V. Rau). 0022-1139/01/$ – see front matter # 2001 Published by Elsevier Science B.V. PII:S0022-1139(01)00368-2