The Nature of Hydrogen Bonding Involving the Siloxane Group

Variation of the Si–O–Si angle in siloxane compounds is a way to tune their basicity from highly hydrophobic systems at linear geometry to hydrophilic systems at small angles. This has great potential in the design of new siloxane materials with properties distinct from those of known silicones. We investigate hydrogen bonds with the siloxane linkage as an acceptor in a large range of Si–O–Si angles for the two hydrogen-bonded complexes disiloxane?silanol [(H3Si)2O?HOSiH3] and disiloxane?water [(H3Si)2O?HOH] with free disiloxane [H3SiOSiH3] as reference in a quantum-mechanical ab-initio study. Geometry, electron density, and the electron localizability indicator provide several complementary indicators of hydrogen bonding which show how Si–O–Si angle variation affects the nature and strength of these unusual hydrogen bonds.