The Periodic Table

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1:36 AM

Q: Why are there two infrared vibrational frequencies for the terminal CO ligands of Fe2(CO)9?

I am struggling to rationalise why there are two Infrared vibrational frequencies ($\pu{2082 cm^-1}$ and $\pu{2019 cm^-1}$) for the stretching of the terminal $\ce{CO}$ ligands of $\ce{Fe2(CO)9}$. From my understanding of the structure, all 6 terminal $\ce{CO}$ ligands are equivalent and thus I w...

14 hours later…

Loong

3:53 PM

waiting for the 2021: a year in moderation meta post …

ah, here it is

1,3-feeds

Q: 2021: a year in moderation

As we say goodbye to the old year and welcome the new one, we have a tradition of sharing moderation stats for the preceding calendar year. As most of you here are aware, sites on the Stack Exchange network are moderated somewhat differently to other sites on the web: We designed the Stack Exch...

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4:11 PM

> Please don't call me "u", "y'all"...

6 hours later…

barlop

9:53 PM

@Mithoron you know the definition of molecule that says about one vibrational state.. I know an ionic monomer matches that, but would an ionic lattice match that too?

Mithoron

10:26 PM

@barlop Huh? Molecule needs to be able to withstand vibrations, but that's about very weakly bound atoms - so called van der Waals molecules aren't "true" molecules because they easily fall apart.

barlop

are ionic monomers van der waals molecules?

Mithoron

Molecular NaCl sure does have rowibrational spectrum

barlop

what about 3d polymer / lattice NaCl?

i'm basically trying to see if an ionic lattice matches that definition of molecule that says "An electrically neutral entity consisting of more than one atom (n>1). Rigorously, a molecule, in which n>1 must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state."

Mithoron

While such things are bond like molecules and can be considered extremely large molecules, typically they aren't called like tha =t.

barlop

though technically they do match the definition (there)?

Mithoron

10:31 PM

@barlop That's the definition excluding vdW molecules, not very large ones

Thing is calling a huge monocrystal a molecule is kinda dumb

barlop

when you say excluding vdW molecules, do you mean you'd exclude vdW molecules, or the definition is?

Mithoron

Or misleading, or pointless

barlop

i.e. is the definition flawed in technically including a large crystal?

Mithoron

@barlop This definition^ is precisely for that

barlop

ok so a large crystal fails the vibrational state criteria, while a monomer matches it?

Mithoron

10:34 PM

Oh for the love of... the definition you mention does not exclude big crystals

barlop

ok thanks

Mithoron

You know you're a weird guy?

More to the point there is no clear cut off for big stuff

barlop

yeah.. you are welcome to post an answer to this question chemistry.stackexchange.com/questions/162044/… and I will accept it.. The guy that answered it did contradict himself on another answer. So i'd rather accept an answer from you and you can mention about the lattice technically meeting that defintion and so that definition having an issue.

or if you don't want to that's fine.. either way is good, thanks

Mithoron

No place where you can say this is too big to be a molecule

So I don't think there's a good way to make a definition with upper constraint.

barlop

this tag for molecule chemistry.stackexchange.com/tags/molecules/info mentions that definition though also says "It is, therefore, a necessary requirement to be a molecule, that the atoms are covalently bound to each other, i.e. covalent-compounds."

Though I think you once said, all bonds are covalent in some sense.. or to some extent?

Mithoron

10:39 PM

@barlop Yeah

barlop

So does that quote really mean that to be a molecule it shouldn't be within the ionic area of the electronegative difference spectrum, it has to be within the portion labelled covalent?

Mithoron

I mean that all molecules have covalent component

No matter how "ionic" or metallic or whatever

barlop

And let's say we go by the definition used by the molecule tag, I guess they mean molecules that are called covalent.. But even then the definition is a bit flawed because it is possible to have a "giant covalent structure " with lots of atoms and that wouldn't be a molecule.

Mithoron

Eyeroll you could go on like that forever

barlop

heh ok just being thorough.

thanks

Mithoron

10:46 PM

Bye

barlop

bye thanks

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