Highly Structured Water Networks in Microhydrated Dodecaborate Clusters

We report a combined photoelectron spectroscopy and theoretical investigation of a series of size-selected hydrated closo-dodecaborate clusters B12X12 2–·nH2O (X = H, F, or I; n = 1–6). Distinct structural arrangements of water clusters from monomer to hexamer can be achieved by using different B12X12 2– bases, illustrating the evident solute specificity. Because B–H···H–O dihydrogen bonds are stronger than O···H–O hydrogen bonds in water, the added water molecules are arranged in a unified binding mode by forming highly structured water networks manipulated by B12H12 2–. As a comparison, the hydrated B12F12 2– clusters display similar water evolution for n values of 1 and 2 but different binding modes for larger clusters, while water networks in B12I12 2– share similarities with the free water clusters. This finding provides a consistent picture of the structural diversity of hydrogen bonding networks in microhydrated dodecaborates and a molecular-level understanding of microsolvation dynamics in aqueous borate chemistry.