This invention relates to a new synthetic porous crystalline material, designated MCM-68, a method and novel polycyclic organic cation for its preparation and its use in catalytic conversion of organic compounds. The new crystalline material exhibits a distinctive X-ray diffraction pattern and has a unique crystal structure which contains at least one channel system, in which each channel is defined by a 12-membered ring of tetrahedrally coordinated atoms, and at least two further, independent channel systems, in each of which each channel is defined by a 10-membered ring of tetrahedrally coordinated atoms, wherein the number of unique 10-membered ring channels is twice the number of 12-membered ring channels.