Hydrothermal reaction of sodium metatungstate with the surfactant temp
late cetyltrimethylammonium (CTA) hydroxide gave the salt (C19H42N)(6)
(H2W12O40). Despite the superficial similarity of TEM micrographs and
powder X-ray patterns of this material to those of mesoporous silicate
s, the salt contains unconnected Keggin ions H2W12O406-. These Keggin
ions pack in a puckered layer arrangement and create roughly spherical
cavities for the surfactant micelle counterions. Attempts to remove t
he template cations and condense the inorganic portion of the structur
e invariably lead to dense WO3-x phases. NbxW6-xO19(2+x)(x = 2, 3, 4)
clusters also formed layered salts with CTA cations, which were reacte
d with tetraethyl orthosilicate (TEOS). The TEOS molecules are absorbe
d, presumably into the hydrophobic portion of the structure, and can b
e hydrolyzed to form silica within the salt. Infrared and solid-state
NMR double-resonance spectra show that the silica network is anchored
to the clusters via covalent Nb-O-Si linkages. Extraction of the silic
a-modified salts with HCl/ethanol yields materials with both micropore
s and mesopores and specific surface areas up to 265 m(2)/g.