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–·nH2O (n = 1–7) with a direct comparison to their analogues [B12H12]2–·nH2O 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···H–O
dihydrogen bonds while additional water molecules show substantially
reduced binding energies. Unlike [B12H12]2–·nH2O possessing
a highly structured water network with the attached H2O
molecules arranged in a unified pattern by maximizing B–H···H–O
dihydrogen bonding, distinct structural arrangements of the water
clusters within [B10H10]2–·nH2O 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.