The crystal structure of giuseppettite, the 16-layer member of the cancrinite - sodalite group.

Giuseppettite, chemical formula Na42K16Ca6Si48Al48O192(SO4)10Cl2·5H2O, space group P31c, a=12.856, c=42.256 Å, is the 16-layer member of the cancrinite–sodalite group. It is characterised by an ABABABACBABABABC… stacking sequence of layers. The crystal structure of giuseppettite was solved and refined against data collected at the Elettra synchrotron facility, using a 0.3×0.2×0.2 mm3 single crystal, twinned on (001), lambda=0.9989 Å, R=0.074 for 3769 reflections, R=0.073 for 3706 reflections with Fo>4sigma(Fo). The structure contains two big cages (“giuseppettite” cages) along [0,0,z], and sequences CCSCCCS of “cancrinite” (C) and “sodalite” cages (S) both along [1/3,2/3,z] and [2/3,1/3,z]. Four sulphate groups surrounded by sodium cations, and alternated with potassium cations, are located within the giuseppettite cages, whereas a partially ordered distribution of sulphate groups and chlorine anions occurs within the sodalite cages. The cancrinite cages host sodium cations and water molecules.