Why Doesn't Calcium Form CaN2?

[ProjectFringe]

I know calcium nitride is Ca₃N₂, but why doesn't CaN₂ exist (or at least not that I can find)?

 

[Borek]

Why should it?

 

[ProjectFringe]

Why should it?

*update: sorry this was a mistake (kind of)...

I was thinking about the 2 nitrogen atoms having a double bond with each other and then an ionic bond with the Ca. Is this possible?

 

[Borek]

The answer always lies in stability and energy (free Gibbs energy to be exact).

Taking into account fact metallic Ca can be safely kept under nitrogen, the answer is obviously "no" - even if you will manage to produce such a compound it will happily decompose into a stable mixture.

 

[snorkack]

The answer always lies in stability and energy (free Gibbs energy to be exact).

Taking into account fact metallic Ca can be safely kept under nitrogen, the answer is obviously "no" - even if you will manage to produce such a compound it will happily decompose into a stable mixture.

Does not follow.
NaN₃ violently decays, releasing metal Na:
2NaN₃=2Na+3N₂
not, for example
3NaN₃=Na₃N+4N₂
But just because NaN₃ stores a large amount of energy and, once set off, violently expands airbags does not prevent NaN₃ from being produced and stored in airbags, in large amounts. Ditto about PbN₆. I expect CaN₆ to be likewise stable.
Does N have any other anions that are stable unless set off?
N₂H₂ is well known, unstable and an important chemical intermediary. Does N₂H₂ form any anions?

 

[Borek]

I am not sure what you mean. The question was not about any Ca/N compound, but about a very specific formula and structure - so while you are right azides are kinetically stable, they are not what the OP asked about.

 

[snorkack]

I am not sure what you mean.

My point is that absence of spontaneous formation does not prove a specific compound cannot be kinetically stable.
I found references to diimide, but not comments as to whether diimide anion is stable.

 

[ProjectFringe]

Thanks for the feedback!

 

[EigenState137]

I know calcium nitride is Ca₃N₂, but why doesn't CaN₂ exist (or at least not that I can find)?

Greetings,

CaN2 (Ca[N2]) Crystal StructureES

 

[TeethWhitener]

And here's the paper with the original discovery:
https://pubs.acs.org/doi/10.1021/ic2023677

 

[TeethWhitener]

Taking into account fact metallic Ca can be safely kept under nitrogen, the answer is obviously "no" - even if you will manage to produce such a compound it will happily decompose into a stable mixture.

This confuses thermodynamics with kinetics. You can mix 2 mol hydrogen and 1 mol oxygen at room temperature even though 1 mol water is far more stable than the H₂/O₂ mix, from a thermodynamic (Gibbs energy) perspective. The reason is because the kinetics--the reaction of hydrogen and oxygen at room temperature--is extremely slow. CaN₂ ends up being the same situation: a kinetic barrier prevents the decomposition of the compound into its constituents (although in this case, the kinetic barrier is likely far lower than in the case of the hydrogen-oxygen mixture).

 

[ProjectFringe]

Greetings,

CaN2 (Ca[N2]) Crystal StructureES

Thanks!

1.) I don't have an account with this website so I can't see the structure.
What do the [brackets] around N₂ mean? Does this represent a double covalent bond between the nitrogen atoms in comparison with an ionic bond between Ca and N₂?

2.) Is it also possible for HK[N₂] to exist as well? By this I mean two nitrogen atoms with a double covalent bond and then both a hydrogen atom and a potassium atom forming ionic bonds with the nitrogen atoms. Or will this compound break down into N₂ + HK (potassium hydride)?

 

[EigenState137]

Thanks!

1.) I don't have an account with this website so I can't see the structure.
What do the [brackets] around N₂ mean? Does this represent a double covalent bond between the nitrogen atoms in comparison with an ionic bond between Ca and N₂?

2.) Is it also possible for HK[N₂] to exist as well? By this I mean two nitrogen atoms with a double covalent bond and then both a hydrogen atom and a potassium atom forming ionic bonds with the nitrogen atoms. Or will this compound break down into N₂ + HK (potassium hydride)?

Greetings,

The reference provided by @TeethWhitener shows the crystal structure. I assume that the bracket notation indicates that the nitrogen is structurally N₂ as opposed to two N's. But that is an assumption although one consistent with the crystal structure.

As for HK[N₂], I do not know. The only results I get on Google are to a Hong Kong flu virus. ES

 

[ProjectFringe]

Greetings,

The reference provided by @TeethWhitener shows the crystal structure. I assume that the bracket notation indicates that the nitrogen is structurally N₂ as opposed to two N's. But that is an assumption although one consistent with the crystal structure.

As for HK[N₂], I do not know. The only results I get on Google are to a Hong Kong flu virus. ES

I'm not sure why but I can't see the structure with that article either. Maybe you have to be logged in as well, or maybe I have no idea what I'm doing. Anyway, I think I know what it looks like. Thanks again

 

[EigenState137]

Try the link below which should be the structures. Ca[N₂] is the one on the top left.

Structures

 

[Borek]

Folks, just a quick reminder: the OP admitted in the past they have not even a basic training in chemistry, yet they have tendency to combine random atoms into random compounds. While you are in many ways right, IMHO you are doing the OP disservice reinforcing their misunderstandings of the basic concepts. Discussing exotic cases as if they were a standard and basic chemistry doesn't help to build a required intuition :(

In other words: let's first help the OP define where the box is, then we can start thinking outside of the box. Other way around is calling for problems.

 

[ProjectFringe]

Try the link below which should be the structures. Ca[N₂] is the one on the top left.

Structures

Got it. Thanks again!

 

[TeethWhitener]

IMHO you are doing the OP disservice reinforcing their misunderstandings of the basic concepts. Discussing exotic cases as if they were a standard and basic chemistry doesn't help to build a required intuition :(

OK but the intuition you supplied in post 4 was incorrect. @snorkack gave a better way of thinking about it in post 5 and I pointed out the classic freshman disconnect between thermodynamics and kinetics that plagues beginner chemists. I don't really see anything wrong with how this thread's gone.

 

[ProjectFringe]

Thank you again for all your feedback! I'm grateful that everyone here takes the time to respond to my questions, seeing as how nobody is paid to do so. Any type of feedback is always valuable to me because there is always something I can learn from it. And even if I can't understand anything, maybe someone else can see the response and learn something from it. One great thing I think about having a forum like this is being able to get so many varying opinions. In the end, it is my responsibility to determine the validity of any information provided by others, so nobody else can be held accountable for that. I'm sorry that my questions often seem extreme, but I do think my understanding has grown a lot since joining this forum. I hope one day I will be able to help others by answering some of their questions, but that day is probably a long way off.