Ice VI

Phase diagram of water

• Can be formed from liquid water at 11 kbar by lowering the temperature to approx. -3 °C
• Density: 1.31 g/cm³

Structural features

Crystal structure of Ice VI

• Ice VI is a proton-disordered phase
• it is composed of two independent interpenetrating networks of H-bonded water molecules (shown above in blue and red, respectively)
• the main structural motif is a tricyclic, cage-like water hexamer, similar as in liquid water

A tricyclic water hexamer composed of four-membered rings

• This motif is also found for the silicon atoms in the zeolite edingtonite, see here for comparison.
• The respective topology of the underlying net is edi, a binodal (4,4)-c net with transitivity pqrs = 2343
• Space group: P4₂/nmc (No. 137)
• Crystal system: Tetragonal
• Lattice parameters:
  • a = b = 6.116(1) Å, c = 5.689(1) Å
  • α = β = γ = 90°

Literature:

[1] W. F. Kuhs, J. L. Finney, C. Vettier and D. V. Bliss, Structure and hydrogen ordering in ices VI, VII and VIII by neutron powder diffraction. J. Chem. Phys. 1984, 81, 3612-3623.
DOI: 10.1063/1.448109

Here, you can download the CIF.

Atomistic structure figures were created with:

VESTA
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).

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