Photoelectron Spectroscopy and Computational Study on Microsolvated [B 10 H 10 ] 2- Clusters and Comparisons to Their [B 12 H 12 ] 2- Analogues.

Microhydrated closo -boranes have attracted great interest due to their superchaotropic activity related to the well-known Hofmeister effect and important applications in biomedical and battery fields. In this work, we report a combined negative ion photoelectron spectroscopy and quantum chemical investigation on hydrated closo -decaborate clusters [B ₁₀ H ₁₀ ] ^2- · n H ₂ O ( n = 1-7) with a direct comparison to their analogues [B ₁₂ H ₁₂ ] ^2- · n H ₂ O and free water clusters. A single H ₂ O molecule is found to be sufficient to stabilize the intrinsically unstable [B ₁₀ H ₁₀ ] ^2- dianion. The first two water molecules strongly interact with the solute forming B-H···H-O dihydrogen bonds while additional water molecules show substantially reduced binding energies. Unlike [B ₁₂ H ₁₂ ] ^2- · n H ₂ O possessing a highly structured water network with the attached H ₂ O molecules arranged in a unified pattern by maximizing B-H···H-O dihydrogen bonding, distinct structural arrangements of the water clusters within [B ₁₀ H ₁₀ ] ^2- · n H ₂ O are achieved with the water cluster networks from trimer to heptamer resembling free water clusters. Such a distinct difference arises from the variations in size, symmetry, and charge distributions between these two dianions. The present finding again confirms the structural diversity of hydrogen-bonding networks in microhydrated closo -boranes and enriches our understanding of aqueous borate chemistry.