title: X-Ray Diffraction and Mössbauer Spectroscopy Studies of Pressure-Induced Phase Transitions in a Mixed-Valence Trinuclear Iron Complex.
abstract: The mixed-valence complex Fe3 O(cyanoacetate)6 (H2 O)3 (1) has been studied by single-crystal X-ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mössbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure-induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mössbauer spectra show that the complex becomes partially valence-trapped after the second phase transition. This sluggish pressure-induced valence-trapping is in contrast to the very abrupt valence-trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure.
authors.affiliation: Center for Materials Crystallography, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark.
authors.forename: Solveig R
authors.initials: SR
authors.lastname: Madsen
authors.affiliation: Instituut voor Kern- en Stralingsfysica, KU Leuven, 3001, Leuven, Belgium.
authors.forename: Haraldur P
authors.initials: HP
authors.lastname: Gunnlaugsson
authors.affiliation: University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh, EH9 3FJ, Scotland, UK.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Moggach
authors.affiliation: Center for Materials Crystallography, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark.
authors.forename: Espen
authors.initials: E
authors.lastname: Eikeland
authors.affiliation: Center for Materials Crystallography, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark.
authors.forename: Lai-Chin
authors.initials: LC
authors.lastname: Wu
authors.affiliation: Deutsches Elektronen Synchrotron FS-PE, Hamburg, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Leupold
authors.affiliation: Center for Materials Crystallography, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Overgaard
authors.affiliation: Center for Materials Crystallography, Department of Chemistry, Aarhus University, Langelandsgade 140, 8000, Aarhus C, Denmark. bo@chem.au.dk.
authors.forename: Bo B
authors.initials: BB
authors.lastname: Iversen
keywords: Mössbauer spectroscopy; electron transfer; high-pressure crystallography; mixed-valent compounds; trinuclear carboxylate