Die Deprotonierung von Metall-Aquoionen I.: Be · aq2+ Solvatations-Isomerie

The reaction of Be · aq²⁺ with OH^? leeds not only to loss of protons by the metalaquo ion but also to structural changes in the solvation sphere. These can be studied by following the pH variations during the first decisecond after mixing the solutions of metal salt and alkali hydroxide. The equilibrium Be²⁺ ? BeOH⁺ is reached within 5 milliseconds if acid free Beryllium solutions are used. If the metal solution is strongly acidic, however, the establishment of the equilibrium needs more time because of the slowness of the process H⁺ + BeOH⁺ → Be²⁺ (k ～ 10⁵ M^?1, s^?1). The extraction of two protons produces in the first instance an unstable Be(OH) species which transforms into the stable isomer Be(OH)₂ (solvatation isomerism) in a first-order reaction of half-life of 7 ms. This isomerisation causes almost complete disappearance of BeOH⁺ from the equilibrium Be²⁺ ? BeOH⁺ ? Be(OH)₂. (KAKIHANA & SILLEN state that the relaxed solutions contain only Be²⁺, Be(OH)₂, Be₃(OH) and some Be₂OH³⁺.) The formation of the polynuclear species Be₃(OH) needs about 30 seconds to go to completion.