The molecular sieve MCM-22 contains structural features previously uno
bserved in this class of materials. Its framework topology, derived fr
om high-resolution electron micrographs and refined with synchrotron x
-ray diffraction powder data, contains two independent pore systems, b
oth of which are accessed through rings composed of ten tetrahedral (T
) atoms (such as Si, Al, and B). One of these pore systems is defined
by two-dimensional, sinusoidal channels. The other consists of large s
upercages whose inner free diameter, 7.1 angstroms, is defined by 12 T
-O species (12-rings) and whose inner height is 18.2 angstroms. These
coexisting pore systems may provide opportunities for a wide variety o
f catalytic applications in the petrochemical and refining industries.
Another structural feature is an unusual-T-O-T-chain that passes thro
ugh the center of a modified dodecasil-1H [4(3)5(6)6(3)] cage.