Σldritch
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Some insight into transition metal-oxygen chemistry (MO4, MO6 ions)
A few years ago i stumbled across this line while browsing atomistry (link) :
| Quote: |
When a dilute solution of a nickel salt is electrolysed at 70° C. in the presence of chromic acid and an alkali pyrophosphate, the tetroxide, NiO4 is
obtained. |
At the time i thought such a compound could newer exist but revisiting it after having learnt more of superatoms i think it, along a few other similar
compounds, do exist. The key to finding these compounds is to consider the oxygen as a two electron ligand and then consider the stable geometries.
Beginning with tetrahedral the following compound/ions should exist (along with some heavier analogs):
NiO4 (8 electrons to reach 18, each O-atom contributes 2, 8 total) Atomistry lends some credance to its existance.
CoO4(-1) (9 electrons to reach 18, each O-atom contribute 2, 8 total, charge 1) This paper lends that prediction some credance. I would expect this ion to be far more stable in aqeous solution than ferrate too.
FeO4(-2) (10 electrons to reach 18, each O-atom contribute 2, 8 total, charge 2) I think we can all agree this ion most definitively exists.
MnO4(-3) (11 electrons to reach 18, O-atoms contribute 8, charge 2) This one exists too. I would guess the only reason this ion exists in
solution is becuase of the closed shell. Compare for instance Mn(IV) and Mn(III); they are far harder to get into solution even with lower oxidation
states. This also means MnO4(-1) is missing two electrons which is probably why it is so reactive.
As neutral superatoms these would be (in listed order): a noble gas, a halogen, a chalcogen and a pnictogen. CoO4 is probably be a beast of an
oxidizer then.
Then more more speculatively we could look at octahedral metal-oxygen clusters. Here we run out of electrons but these complexes can obviously not be
understood well with formal oxidation states so that may not be a problem. Still heavier elements may be better able to accomodate 6 ligands and the
post-lathanides do have enough electrons to actually reach their formal oxidation states. Because of that and to keep this brief i will just mention
the neutral cluster:
CrO6 (12 electrons to reach 18, each O-atom contributes 2, 12 total) I think this one is unlikely to exist but chances should be much better for the
tungsten analog WO6. This would also be the ultimate metal oxide for a thermite.
There could also be oxygen rich cations such as CuO4(+) and ReO6(+) which would be interesting from an energetics design point of view. Anyway i hope
this way of viewing oxometalates is useful, interesting, or both, even though i can make no experimental contribution to back this up at this time.
This does seem very accesible to the amateur though.
EDIT:
I think i found one of the cations in atomistry (link) :
| Quote: |
Electrolysis of Silver nitrate solution at 0° C. yields at the anode a black, crystalline substance of metallic lustre. It readily loses oxygen,
Silver nitrate entering into solution, and the residual crystals of silver peroxynitrate have the formula 2Ag3O4,AgNO3. It changes slowly, with
evolution of oxygen, into 3Ag2O,AgNO3. According to Weber, the presence of between 15 and 25 per cent, of nitric acid inhibits the deposition of the
peroxynitrate at the anode, but produces a brown solution. Weber regards the oxide portion of the salt as having the formula Ag(AgO2)2, analogous to
that of magnetic iron oxide, and considers it to be the silver salt of an unstable argentic acid, HAgO2. It is a compound of silver in which the metal
has a valency greater than unity. |
I think that brown solution is AgO4(+). Maybe the deposited compound is
AgO4NO3. It makes sense it would have low solubility similar to Potassium Nitrate.
[Edited on 22-9-2021 by Σldritch]
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Sulaiman
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Just out of curiosity ;
What tests could positively identify such products?
CAUTION : Hobby Chemist, not Professional or even Amateur
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Σldritch
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Well as i said NiO4 should be a superatomic noble gas so it should be volatile. I would guess much more so than nickel carbonyl considering its lower
mass and the low polarizability of oxygen. It probably comes of as a coloured vapor from the electrolysis, and i bet that is how it was discovered. I
guess it would oxidize wet paper depositing NiO, that might make a good test otherwise. Perhaps CrO6 could form under the same conditions but you
should be able to disinguish the deposited metal oxides from eachother in solution.
As for the non-volatile anions i think titration might be the best bet. Something like fusing Potassium Hydroxide and Potassum Nitrate/Chlorate and
then titrating with something that does not react with Nitrate/Nitrite/Chlorate/Perchlorate in aqeous solution and finally precipitating the metal
sulfide or whatever. From there you can back calculate oxidation state.
As for the cations i have no idea how to make them or test for them. Haven't thought much about them until making this post actually.
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DraconicAcid
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Atomistry, in my experience, is full of non-vetted "facts". I don't believe for a minute that you can make nickel tetroxide or chromium hexoxide. If
you think you can isolate [AgO4]NO3 as a solid...be my guest- there will be a Nobel prize in it for you.
The 18-electron rule doesn't apply to metals in high oxidation states.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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valeg96
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From my very naive point of view this all sounds like some marvelous speculative chemistry only. Like how you can play with nomenclature and
technically say that thiosulphate is the anion of thiosulphoric acid... Well, technically yes but also no... This works wonderfully with oxosalts of
S, P and As but most compounds don't actually exist.
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Σldritch
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Quote: Originally posted by DraconicAcid  | Atomistry, in my experience, is full of non-vetted "facts". I don't believe for a minute that you can make nickel tetroxide or chromium hexoxide. If
you think you can isolate [AgO4]NO3 as a solid...be my guest- there will be a Nobel prize in it for you.
The 18-electron rule doesn't apply to metals in high oxidation states. |
I realize now that i misinterpreted the text. Also it makes no sense for AgO4NO3 to dissolve into additional nitric acid nor for it to decompose into
crystals. Also HNO3 should not be a strong enough acid.
I'm not sure the 18 electron rule is the deciding factor here for stability though it sure looks like it is a part of it to me. Another way of looking
at the tetrahedral complexes is as if they have four double bonds to the metal. That makes 8 pi electrons = 2(n + 1)2 so they are
spherically aromatic as well as 18 electron complexes. Not sure you can do that though, i have never seen this applied to a metal complex like this.
This speaks against the octahedral complexes since they would not be spherically aromatic. The carbonyls still exist though.
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DraconicAcid
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The 18 electron rule applies to low-valent metals with ligands such as carbonyls, alkenes, and phosphines. It does not apply at all with complexes
containing only halo- or oxo- ligands. Yes, you can have stable MO4 ions where M is a d-zero metal (V(V), Cr(VI), Mn(VII), Os(VIII)), but I can't see
how you can get 18 valence electrons in them. I count 16 at best.
"Spherically aromatic"? Where does this concept come from? I've never heard of aromaticity in anything but a planar ring.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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unionised
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"When a dilute solution of a nickel salt is electrolysed at 70° C. in the presence of chromic acid and an alkali pyrophosphate, the tetroxide, NiO4
is obtained"
Says who?
I don't believe it.
And my unevinced denial is just as valid as Atomistry's unevinced claim.
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DraconicAcid
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And I have now learned something from this thread.
https://www.wordsense.eu/evince/
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Boffis
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Mmmm. Has anyone got a reference to the NiO4? How was it detected in the first place? It probably has a have life of a few nano-seconds.
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Σldritch
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| Quote: Originally posted by DraconicAcid | The 18 electron rule applies to low-valent metals with ligands such as carbonyls, alkenes, and phosphines. It does not apply at all with complexes
containing only halo- or oxo- ligands. Yes, you can have stable MO4 ions where M is a d-zero metal (V(V), Cr(VI), Mn(VII), Os(VIII)), but I can't see
how you can get 18 valence electrons in them. I count 16 at best.
"Spherically aromatic"? Where does this concept come from? I've never heard of aromaticity in anything but a planar ring. |
The point is the 18 electron complexes are more stable than they have any right to be. Ferrate is an insanely strong oxidizer yet it can form in
aqeous solution. Vanadate, Chromate, Permanganate and Osmates do not come close to the oxidizing power of Ferrate. In acidic solution Ferrate's
standard electrode potential is as close to Fluorine as it is to Dichromate. It should not exist, yet it does. Stars (electrons) would need to align
for it, and i am trying to figure out how to align them so more similar compounds can be found. CoO4(-) and NiO4 seem to be stabilized the same way as
Ferrate. The first has been predicted to be stable and the second has a synthesis on atomistry. What i am saying is if you go looking for these
compounds i think you have a good chance of finding something interesting.
As for aromaticity i suggest you simply take a look at the wikipedia page.
Also, about CoO4(-), i changed my mind. It should be less stable than Ferrate in solution being a stronger oxidizer but more stable as a anhydrous
salt due to its greater acidity. It probably does not exist in acidic solution because Ferrate forms right before Hydroxyl radical formation under the
same conditions.
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wg48temp9
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Complexes are just so oddball to me. I guess ultimately the atoms will share electrons and if the sharing is low energy than the not sharing it can
happen.
Here is the paper from one of the links above:
Attachment: sup-halogens-srivastava2015.pdf (842kB)
This file has been downloaded 262 times
The paper is an interesting read. Apparently NiO4 is actually NiO2 complexed with O2. From the paper:
"Ferromagnetic metals such as Fe, Co and Ni belong to the 3d transition metal series. Gutsev etal. [22] have estimated the EA of
FeO4, 3.8eV, which is higher than that of Cl. Therefore, FeO4 belongs to the class of superhalogens. Recently, we have performed a systematic
study on the nickel group transition metal oxides [23]. We have noticed that the EAs of NiOn for n≥3 are higher than those of
halogen. However, for n=4, NiOn exists in the form of (NiO2)O2 complex rather than in tetra-oxide form. A natural question arises about Co,
can it form stable tetra-oxide, i.e., CoO4"? Note that Co possesses valence configuration of 3d74s2 and hence its oxidation state ranges from +2 to
+5. In present study, we discuss the structures of neutral and anionic CoOn up to n=5. Their stabilities are analyzed by considering the
dissociations to O atom and O2 molecule.
I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
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Σldritch
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Im not sure i would trust those calculations too much. In the paper (link) where FeO4(-) was proved to exist they say the following:
"Early claims of the existence of Fe(VIII) of the experimentally prepared FeO4 have been proven to be incorrect[9,17]. Both anion
photoelectron spectroscopy and matrix-isolation infrared spectroscopic experiments indicate that the observed FeO4 species in solid argon is due to
(η2-O2)FeO2 peroxide complex of iron dioxide with Fe in oxidation state VI, and that the tetrahedral
Fe(VIII)O4 is not formed[26,27]. The previous theoretical calculations predicted that tetrahedral Fe(VIII)O4 isomer
was stable[26,29], but recent more advanced theoretical studies has revealed that Fe(VIII)O4 is only meta-stable when
comparing with (η2-O2)FeO2 in gas phase."
It was published a few years after the other one i think. They seem to have had a lot of trouble getting accurate computational results in this study.
Whether that is applicable to the other clusters i am not sure. It may have been mostly because FeO4(-) has two isomers with very close
energy that interconvert photochemically but the non-existance of FeO4 says otherwise. The fact that this group did experimental in
addition to computations adds to their credibility.
Still matrix isolation is not that impressive either. I have not been able to find any other information on FeO4(-). I wonder if it could
be related to those reports of perferrate? Perferrate is supposed to be green but i saw nothing close to visible light in that paper.
[Edited on 25-9-2021 by Σldritch]
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