High-Pressure Neutron Diffraction Study of Superhydrated Natrolite

Neutron powder diffraction data were collected on a sample of natrolite and a 1:1 (v/v) mixture of perdeuterated
methanol and water at a pressure of 1.87(11) GPa. The natrolite sample was superhydrated, with a water
content double that observed at ambient pressure. All of the water deuterium atoms were located and the
nature and extent of the hydrogen bonding elucidated for the first time. This has allowed the calculation of
bond valence sums for the water oxygen atoms, and from this, it can be deduced that the key energetic factor
leading to loss of the additional water molecule upon pressure release is the poor coordination to sodium
cations within the pores.