Na-2[B18Se16]: The first 3D polymeric selenoborato-closo-dodecaborate

Systematic studies on selenoborates containing a B-12 cluster entity and alkali metal cations led to the new crystalline phase Na[B18Se16] which consists of a icosahedral B12 cluster completely saturated with trigonal-planar BSe3 units and sodium counter-ions. The cluster entities are connected to each other via seleno- and perselenobridges. Thus a three-dimensional network results with [(B18Se12Se6/2)(n)](2-) - and [(B18Se15Se6/2)(n)](2-) anions in a ratio of 2:1. The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 degrees C. Na-2[B18Se16] crystallizes in the trigonal space group P (3) over bar (no. 147) with a 17.021 (1) angstrom, c = 8.903(1) angstrom and Z = 3.