Question

How do I explain this aquation?

Answer 1

Q: The aquation rate (substitution with water) of Ru (III) chloro complexes vary enormously: The complex hexachloro ruthenium (III) -> [RuCl6]3- has a half lifetime of a few seconds, whereas the half lifetime of pentaaquachloro Ruthenium (II) -> [RuCl(H2O)5]2+ was measured to be about one year. How do you explain this? Which mechanism would you argue this follows (association or dissociation)?



I am really unsure about the answer to this. This is what I THINK could be a possible answer:
Seeing as how RuCl6] 3- and RuCl(H2O)5] 2+ both have different electron count, RuCl6] 3- has 9 electrons in it's d-orbital, while RuClH2O5]2+ has 6? And since both ligands (H2O and Cl) as high-spin, weak field ligands, the hexachloro complex would exhibit a faster substitution (Jahn-Teller), based on it's crystal field splitting. I also argued that since the hexachloro complex has a 3- charge while the pentaaquachloro complex has a 2+ charge, there's a higher chance of exchange since the metal to ligand bonding would tend to increase the rate. Less of a stronger metal to ligand bond due to the high negative charge.
As far as what mechanism it would undergo, I am really unsure but I am guessing dissociation? To lower the ligand field stabilization energy in the t2g?