MS36-P37 Solid State Thermochromism in an Octahedral Co(ii) Complex Studied by X-Ray Powder Diffraction Rosario Pedrero Marín (Organic and Inorganic Chemistry Department. University of Extremadura, Badajoz, Spain) Fernando José Barros-García (Organic and Inorganic Chemistry Department. University of Extremadura, Badajoz, Spain) Álvaro Bernalte-García (Organic and Inorganic Chemistry Department. University of Extremadura, Badajoz, Spain) Francisco Luna-Giles (Organic and Inorganic Chemistry Department. University of Extremadura, Badajoz, Spain)email: rospema@unex.esThermochromism is the phenomenom known as the reversible change in the colour of a compound when it is heated or cooled [1]. This process can take place over a wide (continuous thermochromism) or a narrow (discontinuous thermochromism) range of temperature. The latter, typical of inorganic substances, may be associated to a structural phase transition [2].
In the present work, we have studied the colour change in the pink octahedral cobalt (II) complex [CoCl2(PyTn)]·2H2O [PyTn: 2-(pyrazol-1-yl)-2-thiazoline] [3] in the solid phase over a temperature range from 30ºC to 160ºC by means of powder X-ray diffraction. This compound, previously studied in solution, transforms into the blue dinuclear asymmetrical complex [CoCl2(µ-Cl)2Co(PyTn)2]. The thermochromic transition temperature is considerably higher in the solid state than in solution, as it was expected.
Colour transformation was monitored by means of in-situ X-ray powder thermodiffraction with the aim of discovering reaction intermediates. The X-ray experiment was carried out on a Bruker D8 Advance powder diffractometer equipped with a temperature chamber, using CuKα1 radiation. Measurements were made in the 10‑30º2θ range and collected at temperature intervals of 5ºC.
Reaction product was identified by comparing the measured patterns to the simulated one for known single crystal structure using Mercury CSD software. In additon, TG-DTG curves were obtained in a dynamic air atmosphere in the same temperature range, as well as a DSC curve. From these, it can be concluded that only the two crystallization water molecules are released, keeping the compound its integrity.
 
References:

[1] Day, J. H. (1968). Chem. Rev., 68, 649-657.

[2] Van Ooort, M. J. M. (1988). J. Chem. Ed., 65, 84.

[3] Bernalte-García, A., Lozano-Vila, A. M., Luna-Giles, F. & Pedrero-Marín, R. (2006). Polyhedron, 25, 1399-1407.

Keywords: thermochromism, X-ray powder thermodiffraction, cobalt (II) complex