A new silicogermanate, SU-12, |(CH 3 CH 2 CH 2 NH 3 ) 3 (H 2 O) 2.5 |[(Ge 6.44 Si 0.56 )O 14.5 F 2 ], with 24-ring channel systems was synthesized under hydro/solvothermal conditions, and its structure was determined by single-crystal X-ray diffraction. It is the first silicogermanate with extra-large 24-rings templated by a primary monoamine. Crystallographic data: tetragonal, space group I 4̄2 m, unit cell parameters a = 27.6460(22) Å and c = 17.0885(14) Å, V = 13060.8(17) Å 3, Z = 16, ρ calcd = 1.797 g/cm 3, R1 = 0.0512 [5471 observed reflections with I > 2σ( I )], wR2 = 0.1487, S (goodness-of-fit on F 2 ) = 1.08. SU-12 has a structure topology similar to that of the pure germanate ASU-16. However, the symmetry of SU-12 is higher than that of ASU-16, and the 24-rings become more circular than those in ASU-16. The interaction between the templates and framework is compared for ASU-16 and SU-12, and their thermal stabilities are studied. The orthorhombic ASU-16 is thermally less stable than the tetragonal SU-12 and transformed to SU-12 by heating. The ion-exchange property of SU-12 is also studied.
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