Role of Cation Size on the Structural Behavior of the Alkali-Metal Dodecahydro-<i>closo</i>-Dodecaborates

The last unknown crystal structure among the alkali-metal dodecahydro-closo-dodecaborates (A2B12H12), that of Na2B12H12, was determined by powder X-ray diffraction. Compared to the structural symmetries of its neighboring, cubic, alkali-metal analogs, i.e., the lighter Li2B12H12 (Pa3̅) and the heavier K2B12H12 (Fm3̅), Na2B12H12 displays an intermediate monoclinic (P21/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.