Mechanistic investigations of Al(OH)₃ oligomerization mechanisms.

Aluminum aerogels have extremely low thermal conductivities, and are ideal candidates for use in thermal superinsulators, adsorbents, sensors, catalyst carriers, and inorganic fillers. In the present work, the oligomerization mechanisms of Al(OH)3 were investigated systematically with the Gaussian 03 package at the B3LYP/6-311++G(d,p) level in combination with CPCM single-point energy calculations. The results of our theoretical model showed that: (1) the Al atoms are tetracoordinate and pentacoordinate; (2) in alkaline solution, Al(OH)3 tends to condense into more soluble polyhydroxy compounds; (3) the neutral dimerization of Al(OH)3 and the transfer of the hydrogen on the bridging hydroxyl are energetically favorable, but the most stable geometry is a four-membered Al-O ring structure linked by two bridging hydroxyls; (4) Al(OH)3 is inclined to form tetracoordinate oligomers, which develop into three-dimensional structures connected by four-membered Al-O rings.