Abstract
The two end‐member series of hydro‐sodalites show different structural expansion characteristics during dehydratation at elevated temperatures (300–900 K). The anomalous expansion in cell volume which is observed for series Na6[AlSiO4]6 · nH2O upon loss of 0 < n ≤ 8 H2O is correlated to the destruction of the significant hydrogen bonding system between non‐framework and framework oxygen atoms of the corresponding sodalite structures. The contraction of the unit cell of the basic sodalites Na8[AlSiO4]6(OH)2 · nH2O upon loss of 0 < n ≤ 4 H2O, however, is well understood in terms of space filling of the non‐framework constituents and some special stereochemical features amongst sodium, oxygen and hydrogen atoms.

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