High-pressure synthesis and crystal structure of the mixed valent iron borate Fe8B15O28(OH)8

The new mixed valent iron borate Fe8B15O28(OH)(8) was synthesized under high-pressure/hightemperature conditions of 12 GPa and 850 degrees C in a multianvil device (Walker-type module). It crystallizes with four formula units in the tetragonal space group I4(1)/a with the structural parameters a = 1142.3(2) and c = 1537.4(2) pm (V = 2.006(1) nrn(3), R-1 = 0.0586, wR(2) = 0.0721 (all data)). Fe8B15O28(OH)(8) is composed exclusively from corner-sharing BO4 tetrahedra and can be described as two identical interpenetrating three-dimensional networks that are built up from B11O28 building blocks and interconnecting BO2O(OH) units. The Fe-II and Fe-III ions in (FeFeB15O28)-Fe-II-B-III(OH)(8) are located in the interspaces between the two networks. Fe-57 Mossbauer, Raman, and infrared spectroscopic data are reported. (C) 2013 Elsevier Masson SAS. All rights reserved.