Variable-Temperature and Variable-Pressure 17O-NMR Study of Water Exchange of Hexaaquaaluminium(III)

✍ Scribed by Deirdre Hugi-Cleary; Lothar Helm; André E. Merbach

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 595 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680302

✦ Synopsis

The transverse relaxation rate of H 2 0 in AI(H20)F has been measured as a function of temperature (255 to 417 K) and pressure (up to 220 MPa) using the I70-NMR line-broadening technique, in the presence of Mn(I1) as a relaxation agent. At high temperatures the relaxation rate is governed by chemical exchange with bulk H,O, whereas at low temperatures quadrupolar relaxation is prevailing. Low-temperature fast-injection I70-NMR was used to extend the accessible kinetic domain. The samples studied contained A13+ (0.5 m), Mn2+ (0.24.5 m). H+ (0.2-3.1 m ) and "0-enriched (2040%) H,O. Non-coordinating perchlorate was used as counter ion. The following H,O exchange parameters were obtained: k::* = (1.29 f 0.04) s-', AH* = (84.7 * 0.3) kJ mol-I, AS* = + (41.6 f 0.9) J K-' mol-', and AV:, = + (5.7 ?C 0.2) cm3 mol-I, indicating a dissociative interchange, I,, mechanism. These results of H 2 0 exchange on Al(H,O)P are discussed together with the available complex-formation rate data and permit also the assignment of I, mechanisms to these latter reactions.