Photoelectron Spectroscopy and Computational Study on Microsolvated [B10H10]2- Clusters and Comparisons to Their [B12H12]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 [B10H10](2-)<middle dot>nH(2)O (n = 1-7) with a direct comparison to their analogues [B12H12](2-)<middle dot>nH(2)O and free water clusters. A single H2O molecule is found to be sufficient to stabilize the intrinsically unstable [B10H10](2-) dianion. The first two water molecules strongly interact with the solute forming B-H<middle dot><middle dot><middle dot>H-O dihydrogen bonds while additional water molecules show substantially reduced binding energies. Unlike [B12H12](2-)<middle dot>nH(2)O possessing a highly structured water network with the attached H2O molecules arranged in a unified pattern by maximizing B-H<middle dot><middle dot><middle dot>H-O dihydrogen bonding, distinct structural arrangements of the water clusters within [B10H10](2-)<middle dot>nH(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.