High-accuracy bond lengths from EXAFS of solid KMnO4and MnO4-in aqueous solution

Abstract

Bond lengths and coordination numbers of the nearest neighbours of the central Mn atom in solid KMnO₄ and MnO₄^- in a 0.4 molar aqueous solution have been determined from the extended X-ray absorption fine structure (EXAFS) above the Mn K-edge. In the solution the authors find one shell of four oxygen atoms with a distance of 0.1649+or-0.0005 nm from the central Mn atom. In crystalline KMnO₄ they observe a beating in EXAFS due to the superposition of contributions from two close-lying shells. A comparison of the phases and envelope functions of EXAFS of KMnO₄ and MnO₄^- yields a separation of 0.0125+or-0.0003 nm for these shells. With the bond length in the solution they find three closer oxygen atoms at a distance of 0.1634+or-0.0008 nm and one more distant atom at 0.1759+or-0.0008 nm.