BromicAcid
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What do you know about the +5 oxidation state of nickel?
I've always been fascinated by high oxidation state compounds and once again something has caught my eye. Browsing around online today I ran
across some information on hard soft acid base chemistry, as I was reading through it, one thing caught my eye:
| Quote: | | For example, a metal in a low oxidation state, such as Ni(0), is a soft acid that is stabilized when surrounded by soft bases, such as CO in Ni(CO)4.
But in a high oxidation state, such as Ni(V), the metal is a hard acid that is stabilized by hard bases, such as oxide ions in NiO4(3–).
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So of course I was like, +5 nickel... I've heard of the +3 fluorides, maybe something on +4 compounds,
but +5 compounds? So I did some searching online, (Complicated by V also being a symbol for voltage and nickel hydride batteries being so popular).
Nickelate gave results for the +3 compound, usually sodium nickelate NaNiO2 but nothing really productive and other attempts were also met with
failure. It would be nice if there was a book entirely on high oxidation state compounds, I would read it cover to cover but I've yet to find
one. I might look at some of the common references in the library tomorrow, like "Advanced inorganic chemistry" and such but as for now,
does anyone know something about Ni (V) salts?
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JohnWW
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It appears very hard to search on Google for "Ni(V)". Their search engine disregards punctuation marks like brackets.
There is a possibility that Ni(V) just might exist, but it would be marginally stable only at low temperatures, and as an anion in an alkaline
environment. I think I have heard of NiO2, obtained electrolytically, but it may be a peroxide.
Co(V) would be more likely to exist, in view of the relative ease of obtaining Fe(VI), and the existence of CoO2.
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chemoleo
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Checking 'Advanced inorganic chemistry' by Cotton and Wilkinson, it makes NO mention of Ni +V compounds- even though this book goes on about
all the other oxidation states.
+IV
The alkali salts M2NiF6 made by fluorination are red or purple, and oxo speices like BaNiO3 have Ni IV+. Reference: on the M2NiF6 (and possibly
BaNiO3?) is W.W. Wilson and K.O. Christe, Inorg. Chem., 1984, 23, 3261. Maybe you find references inside this references referring to other +IV Ni
compounds.
Indeed, NiO2 is the "peroxide" rather than the true +IV oxide. It is prepared by oxidising alkaline nickel sulphate solutions with NaOCl,
giving a black precpitate of NiO2 * nH2O. This is unstable, being reduced by water, but it is also a useful oxidising agent for organic compounds.
I wonder HOW useful that is, i.e. better than the notoriuosly difficult to handle KMnO4 or H2O2 oxidations?
Brauer mentions only one IV compound, but no V compound. The IV compound is a complex salt.
III
THe compound NaNiO2 and several related ones seem to be genuine, they can be made by bubbling O2 through molten alkali metal hydroxides contained in
Ni vessels at about 800 deg C. Other oxides can by made by heating NiO with alkali or alkaline earth oxides in oxygen. These mixed oxides evolve O2 on
treatment with water or acid.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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BromicAcid
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It may well be that this compound was just mentioned to be an extreme example, maybe not even existing but reasoned with HSAB theory, I know not to
believe everything I see online, but it does appear to be from the ACS which I do give some credibility to, upon asking two chemistry teachers at
school about it today they admitted they have never heard about nickel in a +5 state (but only one of them had heard of a +3 compound). Regardless, I
found nothing on it today in my search through the library, if it does exist, from this information and comparing to other existing high oxidation
states and their preperations, I would guess that it would be fairly unstable, although interesting to learn about.
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chloric1
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If you had your sodium nickelate I wonder about its oxidizing powers. Would it convert alkaline iodide to iodate or even periodate?
Fellow molecular manipulator
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unionised
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OK, I know this is simplistic, but the ionisation potentials for Ni are
7.6, 18.2, 35.2, 54.9, 75.5 and 108 eV
I think Ni(V) is unlikely to occur in any normal comound.
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Kinetic
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Fun with Nickel
Actually, Ni (V) complexes do seem to exist.
According to Gmelin, there are some 23 compounds of nickel containing a Ni (V) cation. Apart from nickel hexafluoride, most appear to be stabilised by
nitrogen donor atoms; there are also a couple of Ni (V) salen based complexes. Your NiO4(3-) doesn't seem to be a known compound. But why not go
further? There are two references given in which Ni (VI) compounds are prepared: Organometallics, 16, 2209-2212 (1997) and
Organometallics, 18, 1597-1605 (1999).
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BromicAcid
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I was at the library today and decided to look up nickel compounds in the "Comprehensive Treatise on Inorganic Chemistry" series, although
inaccuracies do exist in the series, due to its attempts to be exhaustive, it does have quite a bit of interesting information including the
preparation of what are claimed to be +3, +4, +5, +6, and +8 compounds.
At least a page is devoted to pernickelate salts, K2NiO4 and others and goes on to compare their stability to ferrates, saying that "They
resemble the corresponding ferrates, but are more stable. In aq. soln., the alkali ferrates are decomposed in 20 to 30 mins., but the alkali
nickelates decomposed under similar conditions in a few hours." The book also calls the compound K2NiO5 pernickelate, saying that it is made
"....by fusing in a silver vessel a mixture of nickel monoxide and potassium nitrate, and adding potassium dioxide to the hot fused
product."
Also mentioned are nickel hemipentoxide, Ni2O5 and nickel tetroxide NiO4, since I've never really heard about any of this in my advanced books,
most of these compounds are heavily in doubt, but it is interesting none the less, nickel compounds that react readily with room temperature water to
liberate oxygen and such, there are 5 pages on the subject, I will most likely make a PDF and post it here as it is definitely a good read, make some
popcorn and have fun, you know, that kind of fun.
| Quote: | | There are two references given in which Ni (VI) compounds are prepared: Organometallics, 16, 2209-2212 (1997) and Organometallics, 18, 1597-1605
(1999). |
These are not necessarily nickel +5 compounds, they may be complexes, for example in Ni(CO)4 nickel
is zero valent, just accepting the electrons from the donor atom in a dative bond, but not really making a nickel ion, just accepting the electrons in
the empty D orbitals.
[Edited on 1/20/2005 by BromicAcid]
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JohnWW
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Bromic Acid said, "These are not necessarily nickel +5 compounds, they may be complexes, for example in Ni(CO)4 nickel is zero valent, just
accepting the electrons from the donor atom in a dative bond, but not really making a nickel ion, just accepting the electrons in the empty D
orbitals."
This is not quite correct; in Ni metal, and similarly in Pd, the ground state has all 5 3d orbitals completely filled with 10 electrons. This accounts
for the relative inertness of Ni (and of Pd, and of Pt), and their very low positions in the electrochemical series. The one 4s and three 4p orbitals
are vacant, and of sufficiently low energy to allow complete filling by 4 electron pairs from 4 strong ligands, in this case CO, to form the
zerovalent carbonyl, Ni(CO)4, which has sp3 hybridization and no unpaired electrons.
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JohnWW
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Also, I would think that Ni(V) would be about the maximum possible oxidation state of Ni, having in this case most likely 5 unpaired electrons in the
5 3d orbitals, a configuration lending stability to the oxidation state similarly to Fe(III), Mn(II), and Co(IV). This is also in view of Fe(VI) being
a strong oxidant comparable to permanganate, and Co(V) and (VI) and Fe(VII) and (VIII) being of as yet unproven existence; Cu(III) compounds
(steel-blue in color, 8 d electrons) are strong oxidants. The ionization potentials of the respective electrons are a guide. Ni(VI) and (VIII) can be
ruled out; any such claimed compounds would be peroxides.
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JohnWW
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I found two references to "nickel hexafluoride" on Google, but on looking at them they appear to refer to salts of anions like NiF6-- and
NiF6(4-), containing Ni(IV) and (II) respectively.
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BromicAcid
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John WW, I can't find a single website or book showing nickels electron configuration as [Ar] 3d10 it's always listed as [Ar] 4s 2 3d 8
showing that it has one empty d orbital, copper is often the sterotypical element that chooses to have a full d orbital for greater stability,
abandoning one of it's 4s slots. Besides, none of this is relevent to what I posted, the main point was confirmed by you, that nickel could
accept these electron pairs to add to its shell without really being a +5 compound.
| Quote: | | Ni(VI) and (VIII) can be ruled out; any such claimed compounds would be peroxides. |
Exactly as I thought and
stated in my most recent post. And please just edit your first post instead of having three in a row.
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JohnWW
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Except with strong ligands, where the metal-ligand bond strength preferentially forces electron pairing so that the maximum number of pairs of ligand
electrons can be donated, and except very near to all 5 d orbitals being completely filled to form a symmetrical subshell of 10 d electrons, electrons
in d orbitals of transition metals usually prefer to be unpaired wherever possible, as I understand. Look up "ligand field stabilization
energy" (LFSE) in Leslie Orgel's Transition Metal Chemistry.
I am fairly sure that at least in the case of Pd the ground state is 4d-10 with no outer 5s or 5p electrons (this also accounting for the fact that Ag
has a particularly high first ionization potential). So even if Ni is 4s-2 3d-8, it would have two unpaired d electrons, and there would be very
little energy difference between this and the 3d-10 state.
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BromicAcid
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| Quote: | | So even if Ni is 4s-2 3d-8, it would have two unpaired d electrons, and there would be very little energy difference between this and the 3d-10
state. |
Which shows even more that the distinction between S and D orbitals in this case was really not woth
noting, the ONLY point that I was trying to make is that nickel can form complexes.
Back on topic I just scanned in the information from the book, however the scans were huge and crappy so I copied it in by hand. There may be some
very minor spelling errors but I doubt it, I went back over it a few times. If anyone wants I can send the origional scanned document, but below 1.4
megs it's hard to read. Enjoy! 
Attachment: nickeloxides.htm (27kB)
This file has been downloaded 1110 times
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