Unwrapping the Dodecaborane Core: Structure, Electronic Properties, and Chemical Reactivity Across the Complete [B(12)I(n)](-) Series n = 11-1.

Successively stripping the exohedral substituents from the stable -dodecaborate anion [BI] results in structural transformations of the icosahedral B into a (quasi-)planar unsubstituted B unit. Previous studies have revealed that [BI] to [BI] ions contain a closed B unit, while [BI] is the first ion in the series with an opened B unit. Further transitions in geometry, electronic structure, and chemical reactivity across the whole range of fragments [BI] = 11-1 remain elusive. Herein, we report a systematic investigation to explore the chemical properties of these intermediate structures by using negative ion photoelectron spectroscopy (NIPES), ion mobility spectrometry (IMS), gas-phase ion-molecule reactions, and quantum chemical calculations. [BI] ions can be categorized into three groups: (1) very reactive ions with intact (quasi-)icosahedral B cages = 11-8, (2) less reactive ions with open structures = 7-4, and (3) almost unreactive ions with (quasi-)planar structures = 3-1. Preparative mass spectrometry shows that ions with the unsaturated B core (category 2) tend to form smaller, fully substituted -borate anions [BX] = 6-11 with X = I, H, OH on surfaces. In contrast, ions in category 3 cannot be found on the surface and apparently decay into volatile products. This research provides fundamental insights into the physical and chemical properties of B units depending on their substitution level and paves the way for the rational design of boron-rich compounds by using unconventional [BI] building blocks.