Porous silica and polysilsesquioxane with covalently linked phosphonates and phosphonic acids

In this paper we report on synthesis and characterisation of the first phosphonate and phosphonic acid-modified porous silicas and polysilsesquioxanes. The organosilicon phosphonates [(EtO)(3)Si(CH2)(3)PO(OEt)(2)] 1 and [(EtO)(3)Si(CH2)(2)PO(OEt)(2)] 2 have been used to introduce phosphonate and phosphonic acid functionalities to silica and a polysilsesquioxane. Compounds 1 and 2 have been fully characterised (H-1, Si-29, P-31 and C-13 NMR and elemental analysis). Xerogels [from tetraethylorthosilicate (TEOS) or 1,4-bis(triethoxysilyl)benzene (BTESB), and 1 or 2] bearing functionality of the type [O-n/2(EtO)(3 - n)Si(CH2)(m)PO(OEt)(2)] and, after treatment with concentrated HCl, functionality of the type [O-n/2(EtO)(3 - n)Si(CH2)(m)PO(OH)(2)], (n can be 0-2, m = 2 or 3) were synthesised and characterised using solid state Si-29, P-31 and C-13 NMR spectroscopy, elemental analyses and porosimetry measurements. High surface area mesoporous phosphonic acid-modified silicas with a narrow pore size distribution are described.