Penkvilksite-2O: Na2TiSi4O11.2H2O.

The crystal structure of synthetic penkvilksite-2O, disodium titanium tetrasilicate dihydrate, Na(2)TiSi(4)O(11).2H(2)O, a microporous titanosilicate, confirms the major features of a previous model that had been obtained by order-disorder (OD) theory from the known structure of penkvilksite-1M. An important difference from the previous model involves the hydrogen bonding of the water molecule which, on the basis of a Raman spectrum and the finding of only one of the two H atoms, is proposed to be disordered about a fixed O-H direction. The structure of penkvilksite-2O is based on (100) silicate layers linked by isolated TiO(6) octahedra to form a heteropolyhedral framework. The layer is strongly corrugated, based on interlaced spiral chains, and is crossed by two different channels that have an effective channel width of about 3 A.