1 Centre for Research in Molecular Modeling and Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montréal, Québec, H4B 1R6, Canada.

Based on an experimental observation, it has been controversially suggested in a study (Kurotobi et al., Science 2011, 33, 613) that a single molecule of water can completely be localized within the subnano-space inside the fullerene C(60) cage and, that neither the H atoms nor the O lone-pairs are linked, either via hydrogen bonding or through dative bonding, with the interior C-framework of the C(60) cage. To resolve the controversy, electronic structure calculations were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population and bond orbital analyses, and the results were analyzed by using varieties of recommended diagnostics often used to interpret noncovalent interactions. The present results reveal that the mechanically entrapped H(2)O molecule is not electronically innocent of the presence of the cage; each H atom of H(2)O is weakly O-H···C(60) bonded, whereas the O lone-pairs are O···C(60) bonded regardless of the conformations investigated. Exploration of various featured properties suggests that H(2)O@C(60) may be regarded as a unique system composed of both inter- and intramolecular interactions.