MURATAITE, A UB12 DERIVATIVE STRUCTURE WITH CONDENSED KEGGIN MOLECULES

The crystal structure of murataite, space group <F(4)over bar 3m>, a 1 4.886(2) Angstrom, has been solved by Patterson methods and refined to an R of 4.91 (wR 4.71%) for 265 observed reflections (MoK alpha radia tion). The ideal formula is (Y,Na)(6)(Zn,Fe)(5)Ti12O29(O,F)(10)F-4 wit h Z = 4, but its simple appearance conceals extensive cation disorder within the structure. There are four distinct cation sires: the X site is [8]-coordinated and contains (Y,HREE,Na,Ca,Mn); the T site is tetr ahedrally coordinated and contains (Zn,Si); the M1 site is octahedrall y coordinated and contains (Ti,Nb,Na); the M2 sire is [5]-coordinated by a triangular bipyramid and contains (Zn,Fe3+,Ti,Na). Three M1 octah edra share edges to form a compact M(3) phi(13) group. Four of these M (3) phi(13) groups link by sharing corners to form a tetrahedral cage in the center of which is the T site. The resulting Keggin-structured [M(12)T phi(40)](n-) unit may be considered as the fundamental buildin g block of the structure. The net formed by linkage of the M1 polyhedr a is topologically the same as the B net of UB12, which accounts for t he similarity of X-ray properties of murataite and this compound.