Positional isomerism of cluster carbon in monocarbaborane chemistry is rare. Oxidation of the [6-Ph-nido-6-CB 9 H 1 1 ] - anion or the unsubstituted [arachno-6-CB 9 H 1 4 ] - anion with elemental I 2 in alkaline solution gives a quantitative conversion to the previously uncharacterised [2-R-closo-2-CB 9 H 9 ] - anions, where R is Ph or H, respectively; these anions isomerise quantitatively under strong heating to give their previously established [1-R-closo-1-CB 9 H 9 ] - isomers.