Diol-Linked Microporous Networks of Cubic Siloxane Cages

A new class of inorganicorganic hybrid porous materials has been synthesized by a reaction between octa(hydridosilsesquioxane) (H8Si8O12), which has a double-four-ring (D4R) structure, and various diols, such as 1,3-propanediol (PD), 1,4-cyclohexanediol (CHD), and 1,3-adamantanediol (AD). Solid-state 29Si magic-angle-spinning NMR spectroscopic analysis confirmed that most of the corner Si-H groups reacted with diols to form Si-O-C bonds with retention of the D4R cage. Nitrogen adsorptiondesorption studies showed that the products are microporous solids with high BET surface areas (up to approximate to 580 m2g-1 for CHD- and AD-linked products). If n-alkanediols are used as linkers, the surface area becomes smaller as the number of carbon atoms is increased. The thermal and hydrolytic stability of the products strongly depend on the type of diol linkers. The highest stabilities are found for the AD-linked products, which are thermally stable up to around 400 degrees C and remain intact even after being soaked in water for 1 day. In contrast, the PD-linked product is easily hydrolyzed in water to give microporous silica. These results offer a new route toward a series of silica-based porous materials with unique structures and properties.