RAMAN STUDIES OF HYDRATION OF HYDROXY COMPLEXES AND THE EFFECT ON STANDARD PARTIAL MOLAR HEAT-CAPACITIES

Raman spectroscopic studies of aqueous hydroxy complexes B(OH)3, B(OH)4-, Al(OH)4-, Zn(OH)24-, and their deuterated analogues provide compelling evidence for the presence of strong hydrogen bonding of water in the outer solvation sphere to the oxygen of the hydroxy ligand in the first coordination sphere. The deuterated complexes are more strongly hydrogen bonded than the hydrogen complexes. The fact that these hydrogen-bonding effects for the hydroxy borates are much more pronounced than for the aluminate and zincate anions can account for the unexpectedly large differences in the standard partial molar heat capacities of B(OH)4- and Al(OH)4-. The extension of semi-empirical solvation models based on the Born approximation for aqueous hydrolyzed species will need to consider the rather large and specific effect of hydrogen bonding of water to the hydroxide ion.