Water in the solid phase ices

Solid H20 has 11 known crystalline forms, as listed in Table 16.3.1. 

Ordinary hexagonal ice Ih and cubic ice Ic are formed at normal pressures, the latter being stable below — 120°C. Their hydrogen bonding patterns are 

Ice Space group Parameters of unit cell (pm) Z Hydrogen positions Density (g cm-3) Coordination number Hydrogen bond distance (pm) Nearest nonbonding distance (pm) 

In both Ih and Ic, the hydrogen-bonded systems contain cyclohexane-like buckled hexagonal ring motifs chair form in Ic and boat form in Ih. An important distinction is that in Ic all four hydrogen bonds are equivalent by symmetry. In Ih, the hydrogen bond in the direction of the hexagonal axis can be differentiated from the other three. 

A neutron diffraction analysis of H2O and D2O ice Ih at different temperatures has shown that, in addition to the disordered hydrogens, the oxygen atoms are also disordered about sites 6 pm off the hexagonal axis. 

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