Ice Ic

Ice Ic ( Ice one cubic)

• can be formed by condensation of water vapour at reduced pressure well below -80 °C
• is metastable with respect to Ice Ih (approx. + 50 J/mol)
• it seems to be very difficult to grow large phase-pure Ic ice crystals; they contain, to a certain extent stacking-disordered or hexagonal ice

Structural features:

• like hexagonal ice cubic ice is a proton-disordered phase
• every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
• tetrahedrally coordinated
• O-D bond length approx. 101 pm
• D …. O-D distance approx. 174 pm
• O … O distance approx. 275 pm
• 6-membered rings (exclusively chair conformation)

• sometimes also called “cristobalite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO₂ phase cristobalite
• it would be also justified to call it diamond-like ice 🙂
• Space group Fd-3m
  • a = b = c = 6.3510 Å
  • α = β = γ = 90°

 

  Here, you can download the CIF.

[Atomic structure figures 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).]

Advertisement

Ice Ih

Ice I_h (Ice one hexagonal)

Structural features:

• single molecule and molecular arrangement

• Ice Ih is a proton-disordered phase

• every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
• tetrahedrally coordinated
• O-H bond length approx. 99 pm
• H …. O-H distance approx. 175 pm
• O … O distance approx. 275 pm
• H-bond strength: approx. 21 kJ/mol
• 6-membered rings
  • chair-like conformation in the (a,b) plane
  • boat-like conformation along the c direction

(graphic 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).

• sometimes called “tridymite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO₂ phase tridymite
• Space group P6₃/mmc
  • a = b = 4.4975 Å, c = 7.3224 Å
  • α = β = 90°, γ = 120°

 Here, you can download the CIF.