Structural transition at 225 K of the trinuclear Fe(III) heptanoate [Fe3O(O2CC6H13)6(H2O)3]NO3

• Published in: Solid state sciences 2005-10, Vol.7 (10), p.1236-1246
• Main Authors: FRANCOIS, M, SALEH, M. I, RABU, P, SOUHASSOU, M, MALAMAN, B, STEINMETZ, J
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Diamagnetism, paramagnetism and superparamagnetism; Exact sciences and technology; Magnetic properties and materials; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Mössbauer effect; other γ-ray spectroscopy; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory of crystal structure, crystal symmetry; calculations and modeling
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2005.05.008

The trinuclear iron (III) heptanoate [Fe30(O2CC6H13)6(H2O)3]NO3 compound is synthesized and studied by single crystal X-ray diffraction as a function of the temperature, also by Fe57 Mossbauer spectroscopy, electrochemical and magnetic measurements. Its thermal behavior is determined by DSC, TGA and X-ray diffraction. The compound undergoes a structural phase transition at Ts = 225 K giving a superstructure of order two (above Ts: P -1, a = 11.1393(2) A, b = 14.2757(3) A, c = 18.2088(4) A, a = 80.607(1)DG, B = 84.175(l)DG, y = 83.464(1)DG; below Ts: P -1, a = 11.0122(2) A, b = 14.2723(3) A, c = 35.5222(7) A, a = 94.138(1)DG, 0 = 97.136(1)DG, y = 96.779(l)DG). The origin of the transition is interpreted as being due to a 60DG rotation of the nitrate groups of one sheet out of two of the lamellar structure. Analysis of the Fe57 Mossbauer spectra as a function of the temperature does not show electronic transition such as valence trapped phenoma below Ts. The compound has a paramagnetic behavior in the temperature range 300-2 K. A Heisenberg model of interaction based on triangular Fe(III) units of quantum S = 5/2 spins is used for simulating the variation of the susceptibility between room temperature and 2 K.