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.