Pore structure of (NH4)4SiW12O40 sponge crystal was successfully elucidated by means Ar adsorption isotherm analysis combined with molecular probe method and modeling. The pores consist spherical voids or “cages” diameter ca. 12 Å these are connected smaller “windows”. These “windows” clearly resolved in the pore size distribution for first time. Molecular is larger than 8.5 10.2 Å, being consi...