Sodium selenoborato-closo-dodecaborates: structures and properties

Hammerschmidt A, Doch M, Lindemann A, Putz S, Krebs B

Abstract

Systematic studies on selenoborates containing a 13, cluster entity and alkali metal cations led to the new crystalline phases Na-s[B18Se18] Na-6[B18Se17] and Na-2[B18Se16] which were prepared in solid state reactions from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes. Monoclinic Na-8[B18Se18] (space group P2(1)/c) consists of icosahedral B-12 clusters completely substituted with trigoual-planar BSe3 units and sodium counter ions. Na[B18Se17] is also monoclinic, space group C2/c. Icosahedral B-12 cluster entities as found in Na-8[B18Se18] are connected in one direction via exocyclic selenium atoms forming the infinite chain anion ([B18Se16Se2/2](6-))(infinity). hi Na-2[B18Se16] (space group P (3) over bar) the icosahedral B-12 cluster entities are connected to each other via seleno and perseleno bridges. Thus a three-dimensional network results with [B18Se12Se6/2](2-)- and [B18BSe15Se6/2](2-) anions in a ratio of 2:1.