The Topochemical Pseudomorphosis of a Chloride into a Bismuthide

The heterogeneous reaction of crystals of the novel intermetallic subhalide Bi12Rh3Cl2 with a solution of n-butyllithium at 70 degrees C led to the complete topochemical exchange of chloride ions for bismuth atoms, that is, the transformation into the isostructural metastable intermetallic superconductor Bi14Rh3. The crystals underwent the reductive pseudomorphosis almost unchanged except some fissures perpendicular to the a-axis. Detailed inspections of the transformed crystals by electron microscopy indicated no volume defects that would indicate internal chemical reactions. Thus, extensive mass transport must have occurred through the seemingly dense crystal structure. An efficient transport mechanism, based on an unusual breathing mode of the three-dimensional network formed by edge-sharing [RhBi8] cubes and antiprisms, is proposed. The replacement of ionic interaction in the chloride by metallic bonding in the binary intermetallic compound closes the pseudo gap in the density of states at the Fermi level. As a result, the rod-packing of conducting, yet electrically isolated strands of [RhBi8] cubes in Bi12Rh3Cl2 turns into the three-dimensional metal Bi14Rh3.