An ordered form of the extra-large-pore zeolite UTD-1: Synthesis and structure analysis from powder diffraction data

A highly crystalline sample of the extra-large-pore, high-silica zeolite UT D-1 has been prepared in fluoride medium. The resulting product (UTD-1F) ha s a powder diffraction pattern remarkably different from that published for the calcined; form of conventionally prepared UTD-1, and it could only be indexed on a monoclinic unit cell. The crystal structure was determined ab initio in the Space group P2(1)/c from synchrotron Powder diffraction data collected on a textured sample. The resulting structure, with 69 non-H atom s in the asymmetric unit, is by far the largest structure solved directly f rom powder diffraction data to date. Subsequent Rietveld refinement of the structure in Pc, with 349 positional parameters and 464 geometric restraint s, proved to be surprisingly stable and converged with R-F = 0.041 and R-wp = 0.134 (R-exp = 0.101). In contrast to the structure reported for calcine d UTD-1, no evidence of disorder was; found in the UTD-1F framework (struct ure type code DON). There is a strict up-down;alternation of the orientatio n of the Si tetrahedra in the 14-rings, and double crankshaft chains link a djacent 14-ring channels. Not only the framework, but also the (Cp*)(2)Co c omplex, which appeared very clearly on the difference electron density map, was found to be fully ordered in the channels with the 5-fold axis paralle l to the channel direction.