Covalent bonds between the heavy metal cations and the aluminosilicate framework have been discovered to be the cause of distinct structural characteristics in anhydrous sodalites Ag-6[AlSiO4](6) and Tl-6[AlSiO4](6) that differ significantly from their alkali metal containing analogues. Evidence of guest-framework bonding interactions include interatomic distances, shifted IR bands, and quadrupole coupling of aluminum. This bonding results in a reduction of the unit cell size, and a locked in static disorder of the cations. Also of interest are the short Tl-Tl distances seen in Tl-6[AlSiO4](6). These could indicate the formation of Tl-3(3+) species in each cage, resulting in a bce lattice of ionic thallium clusters. Low-temperature synchrotron powder diffraction data, multiple quantum magic-angle spinning (MQ-MAS) NMR, and FTIR studies are presented.