December 14, 2019, 05:12:59 AM
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Topic: Relativistic effects on orbital/electron energies/oxidative potential of Gold  (Read 119 times)

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Offline owk9688

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Hi everyone

I'm having a hard time trying to uderstand how relativistic effects alter the electron energies/ orbital energies/ nucleophilicity of gold complexes relative to what you would expect in a non-relativistic atom.

I'm working with Gold catalysts (1+ and 3+) and one thing a lot of the literature discusses is the extremely low propensity for Au (I) to become oxidized into Au (III). The reason given is that relativistic expansion of the valence 5d orbitals in these species reduces electron/electron repulsion in these filled orbitals, making the electrons lower in energy and thus less nucleophilic than you would expect. This is confusing, because I thought that relativistic expansion of the 5d orbitals would RAISE the energy of those orbitals (since they are moving farther outward from the nucleus). I've found multiple online sources saying just that --relativistic effects cause the 6s orbital to drop in energy while the 5d orbitals are raised (creating a very small energy gap between the two levels which accounts for gold's color)

How am I thinking about this incorrectly? To me, gold's relativistic effects should cause its 5d orbitals to move farther outward from the nucleus, its 5d electrons to thus be higher in energy, less tightly held, and thus easier to oxidize than, say Silver or Copper, and yet the opposite is true.

Any help would be appreciated.

Offline Corribus

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Off the top of my head, I suspect you may be confusing the electronic structure of the neutral gold atom to the electronic structure of a gold cation. Which levels are contracted and expanded in the former may not be the same as those that are contracted and expanded in the latter, much less the quantified energetic interactions of electrons in these levels. In other words, as soon as you remove an electron from the valence shell of a gold atom, the interaction energies - and relativistic effects therein - of all the remaining electrons change.

To get a better idea of the answer I'd have to read through the literature.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

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