Caesium Cobalt Dicarbollide—solubility, Precipitation and Reactivity in Basic Aqueous Solution

The title compound, Cs+[Co((3)-1,2-C2B9H11)2]− (CsCDC), was precipitated with a NaCDC solution from solutions containing CsCl. The reaction was followed by measuring the loss of light intensity as the precipitate formed. [Cs+] and [CDC−] at the point of precipitation were estimated and approximate values of Ksp for CsCDC were determined at room temperature: 8 × 10−6 (water), 7 × 10−6 (1 M NaOH) and 2 × 10−6 (5M NaCl/0.1 M KOH/1.0 M NaOH). In some cases, NaCDC precipitated from solution when added to the latter salt solution. For the medium, 5 M NaNO3/0.1 M KOH/1.0 M NaOH, a four-fold excess of NaCDC was added to a 10 mM Cs+ solution at 40°C and the [CDC−] measured spectrophotometrically. Only CsCDC precipitated, and a Ksp of 3.9 × 10−6 was determined. The solubilities of CsCDC were measured in NaNO3 and NaCl solutions at 30°C as a function of the Na salt concentration. The reaction of the CDC− with OH− slowly produces B(OH)4−, H2 and CoO(OH). The reaction of 22 μM CsCDC 173 with NaOH (1 M) has a first-order rate constant at 56°C of 8.8 × 10−7 s−1, while that for NaCDC (14 mM) is 7.2 × 10−7 s−1. The activation energy for the reaction is 110 kJ mol−1.