Valence trapping of mixed-valence solvated hexakis(acetato)oxotris(pyridine)triiron complex at high pressure

Abstract

The transformation from valence detrapped to valence trapped for two oxo-centered trinuclear iron acetate complexes is studied at pressures up to 95 kbar with the use of a diamond anvil cell. Variable-pressure {sup 57}Fe Mossbauer spectra are presented for {sup 57}Fe-enriched (Fe{sub 3}O(O{sub 2}CCH{sub 3}){sub 6}(py){sub 3}){times}py (1) and (Fe{sub 3}O(O{sub 2}CCH{sub 3}){sub 6}(py){sub 3}){times}CHCl{sub 3} (2), where py is pyridine. At 298 K and applied pressures less than {approximately}20 kbar, each of the complexes gives a spectrum with a single quadrupole-split doublet, which indicates that complexes 1 and 2 are interconverting faster than the Mossbauer time scale under these conditions. Application of pressure in excess of {approximately}80 kbar leads to both complexes becoming valence trapped, as indicated by two doublets in the Mossbauer spectrum with an area ratio of {approximately}2:1 (Fe{sup III}:Fe{sup II}). At intermediate pressures, each of these complexes gives a Mossbauer spectrum that can be fit as a superposition of a valence detrapped doublet and a valence trapped four-line pattern. The nature of the pressure-induced transformations observed in complexes 1 and 2 is discussed with reference to the phase diagram derived from a spin-Hamiltonian theoretical approach that parameterizes intermolecular interactions in terms of the molecular field approximation. more » 11 refs., 4 figs., 2 tabs. « less