Talk:Thiocyanatoiron

Infobox problems

Besides the fact that this article is desperately in need of expansion, I'm not sure any of the infobox is right. That structural formula and name appear to be for a completely different compound. Related, maybe, but not the same. -- 2ReinreB2 (talk) 01:29, 29 March 2016 (UTC)

Strike that, it's just a hydrate. Should've noticed that. Article still needs to be expanded, though. -- 2ReinreB2 (talk) 01:36, 29 March 2016 (UTC)

One possibility

I looked around. This species has never been isolated. It is referred to in hundreds of papers, many either old-fashioned or just old. It is mentioned as an test for Fe(III) in samples. The spot test for Fe(III), mentioned in some textbooks, involves adding SCN- to Fe(III) solution, but there is no discussion in the two books I consulted of what the species really is. A JACS paper from the 1940's shows that it is a 1:1 complex, probably [Fe(NCS)(H₂O)₅]²⁺ (as depicted). A lot of the present article appears to be intelligent conjecture, probably is overstepping what is known, since the literature is so thin on details.

My proposal is to compress the content and shift it to the article ferric, since it is a test for that oxidation state of iron. But counter proposals are welcome. --Smokefoot (talk) 22:42, 6 May 2016 (UTC)

If insufficient data exists then compress back to what is known. That said, it might be worth mentioning the bonding - it looks (to me) like a lovely example of the stabilizing effects of back-bonding, I can't think of many other simple anionic N ligands which are water stable. --Project Osprey (talk) 09:08, 9 May 2016 (UTC)

Actually... how sure are we that this structure is correct? Would isothiocyante (Fe-S) not be more likely? I can find examples in the literature of stabilized complexes containing either version of the ligand but no mention of ligand tautomerisation. It seems like they assume that whichever tautomer the starting material is, then that's the tautomer the complex will possess. I'm not sure it's as clear cut as that and if you're not looking it would be easy to miss. There's probably a good paper in there somewhere. --Project Osprey (talk) 09:42, 9 May 2016 (UTC)

Good feedback. SCN is almost always N-bonded to hard metals, that is settled. There is no discussion of bonding much less backbonding (which would not be expected in h.s. complexes). The literature is old-timey, or 3rd worldly and very applied stuff. People have far better ways to assay Fe. I'll plan to compress and move this junker.--Smokefoot (talk) 12:59, 9 May 2016 (UTC)

That seems best. (Surely there's some back-bonding? The intense colour would strongly suggest a charge transfer complex and that usually means d→π* interactions) --Project Osprey (talk) 13:58, 9 May 2016 (UTC)

Zero back bonding is likely. High spin → never/rarely any pi-backbonding that I know of. One way to think about it (IMHO here and elsewhere) is that bonding in high spin complexes is more ionic whereas pi-back bonding is characteristic of covalent bonding. High oxidation state → rarely any backbonding. For high oxidation states, the t2g levels, which are the donor orbitals in pi-backbonding, are especially low in energy (as are all filled levels), so the energy gap between those levels and the p* levels on the ligand is great, leading to weaker interactions. Charge transfer must be operative because the intensity is so great (hence it is an easily visualized spot test) and all d-d transitions are spin- and Lapporte-forbidden in high spin d5. I would guess that, the band is LMCT, given the high oxidation state. One of these days, we could draw pictures of these things - better explanations could come from User:Dirac.--Smokefoot (talk) 18:33, 9 May 2016 (UTC)

Thanks for taking the time to explain that. --Project Osprey (talk) 13:28, 10 May 2016 (UTC)

Last week I checked the CSD for Fe-SCN and Fe-NCS species. There are a handful of examples of the former, and hundreds of the latter. No smoking gun, though - i.e. no [Fe(NCS)(H₂O)₅]²⁺. --Ben (talk) 23:03, 11 May 2016 (UTC)

The structures wouldnt be in CSD. They'd be in the Karlruhe one. I had checked it. Nada. Kinda weird. Tempted to grow crystals myself.--Smokefoot (talk) 01:44, 12 May 2016 (UTC)

If there are organic cations or solvent molecules, they would be, and the CSD is much easier to search by structure. I tried Karlsruhe, too, and got nothing. Do it! Although I'm surprised it hasn't been done already, which makes me think maybe there's more to this species than meets the eye. --Ben (talk) 11:33, 12 May 2016 (UTC)

If all else fails, Google/Google Scholar. D. R. Dinsdale et al, Dalton Trans. 2015, 44, 11077-11082. They crystallised an [Fe₂(SCN)₁₀]⁴⁻ ion. There's also this, O. I. Kucheriv et al, Acta Cryst. E 2015, 71, 374-376, a co-crystal of a pyrazine and [Fe(NCS)₃(H₂O)₃]. FInally, here's a very old paper from 1941 that seems to be the original of the formula [Fe(NCS)]²⁺: H. E. Bent, C. L. French, J. Am. Chem. Soc. 1941, 63, 568-572. It's old fashioned but they do explain their reasoning in detail. --Ben (talk) 12:01, 12 May 2016 (UTC)

The reaction, Fe³⁺(aq) + SCN⁻(aq) ⇌ [Fe(SCN)]²⁺(aq) is a classic school experiment to show Le Chatelier's principle. One ref here[1] which cover the subject in details, it says the reaction has been used in 125 years (in 1953). Christian75 (talk) 09:23, 15 May 2016 (UTC)

There are more modern education references, including the following: 1998 - ionic strength effect on equilibrium and 2011 - colorimetric determination of K. --Ben (talk) 11:38, 15 May 2016 (UTC)

Great catches all! Well we seem to have enough material. I might try to do the move today. The focus is not only any SCN-Fe(III) species but the 1:1 complex, which is/was used in the colorimetric test. --Smokefoot (talk) 13:30, 15 May 2016 (UTC)