Role of Cation Size on the Structural Behavior of the Alkali-Metal Dodecahydro-closo-Dodecaborates

The last unknown crystal structure among the alkali-metal dodecahydro-closo-dodecaborates (A(2)B(12)H(12)) that of Na(2)B(12)H(12), was determined by powder X-ray diffraction. Compared to the structural symmetries of its neighboring, cubic, alkali-metal analogs, i.e., the lighter Li(2)B(12)H(12) (Pa (3) over bar) and the heavier K(2)B(12)H(12) (Fm (3) over bar), Na(2)B(12)H(12) displays an intermediate monoclinic (P2(1)/n) structural arrangement. This result allows us to understand more thoroughly the effect of cation size on the observed structural behavior of this technologically relevant series of compounds.