An obscure fact I never knew: All of the lanthanides except promethium exhibit a divalent state.

[NNadir]

I was wandering around the scientific literature today and came across this very cool fact:

For many years, only six of the lanthanide metals were thought to be able to form complexes with the metal in the +2 oxidation state: Eu, Yb, Sm, Tm, Dy, and Nd.(1?3) This belief was supported by extensive solid state and solution studies,(1?5) as well as calculations of the reduction potentials.(6?10) However, recent studies of rare earth reduction chemistry have shown that the divalent oxidation state is accessible for all the lanthanides (except radioactive promethium) by reduction of tris(cyclopentadienyl) metal complexes with potassium or potassium graphite in the presence of a chelate.(11?15) This was originally shown with La and Ce by reduction of Cp??3Ln precursors [Cp?? = C5H3(SiMe3)2],(11) and subsequently for all the lanthanides, using Cp?3Ln precursors, (Cp? = C5H4SiMe3).(4,5,12?14) These reactions, as well as results with Th,(16) U,(17,18) and Pu,(19) are summarized in eq 1,

I added the bold.

Trimethylsilyl versus Bis(trimethylsilyl) Substitution in Tris(cyclopentadienyl) Complexes of La, Ce, and Pr: Comparison of Structure, Magnetic Properties, and Reactivity (Chad T. Palumbo, Lucy E. Darago, Cory J. Windorff, Joseph W. Ziller, and William J. Evans, Organometallics 2018 37 (6), 900-905)



Most surprising in this equation is the fact that this holds true for three actinides, thorium, uranium and plutonium. Weird.

I'm glad I found that out before I died.

[Karadeniz]

1. And I'm glad for you!

[eppur_se_muova]

2. Well, cryptate-alkali metal complexes did give us alkali metal anions.

So that's some pretty powerful reducing going on.

[NNadir]

5. Thanks. To be perfectly honest I wasn't familiar with these cryptands, and it looks...

...like they've been around for quite some time.

At a first glance, they look like electrides, with which I have some familiarity in relation to radiation chemistry.

Some of the fun of writing here is that people sometimes tell me things I didn't know; often it's you who does so.

Thanks again.

[eppur_se_muova]

6. Yes, apparently it was electrides that led Dye et al. to try making alkalides originally.

IIRC, there was an article on this in Scientific American when I was in high school -- or maybe not. I just know I came across it at a time when I knew enough about chemistry to find such a thing almost unthinkable. Alkali metals were always cations! But someone thought otherwise. If I search my old notes I might find a record of a lecture from grad school on cryptands, so it's been brought to my attention a couple of times.

https://en.wikipedia.org/wiki/Alkalide

Then there's this:

Rare oxidation states

Less common oxidation states of gold include ?1, +2, and +5.

The ?1 oxidation state occurs in aurides, compounds containing the Au? anion. Caesium auride (CsAu), for example, crystallizes in the caesium chloride motif;[39] rubidium, potassium, and tetramethylammonium aurides are also known.[40] Gold has the highest electron affinity of any metal, at 222.8 kJ/mol, making Au? a stable species.[41]

https://en.wikipedia.org/wiki/Gold#Rare_oxidation_states

and this:

https://www.sciencedirect.com/science/article/pii/S129325580500230X

Apparently both BaPt and Cs2Pt are known.

Oh, and Pekka Pyykö (I love that name!) has predicted that Oganesson - element 118, a "noble gas" element, should form an anion - good thing IUPAC gave that name the nonmetallic -on ending!

[keithbvadu2]

3. I still do not know it.

[lastlib]

4. But can they dance with Ginger Rogers?

Ah, chemistry! (and I had to be a Math geek............)