Talk:Rhodocene

Medical applications of rhodocene or its derivatives?

I have come across reference to an intriguing paper:

Wenzel, M. (1988) Ferrocene, ruthenocene, and rhodocene analogs of haloperidol - Synthesis and organ distribution after marking with ¹⁰³Ru or ^103mRh. Applied Radiation and Isotopes, 39(12), 1237-1241.

I have not heard before of any medical / biological application of rhodocene, but this paper seems to indicate that there may be such applications. Unfortunately, I don't have access to the paper itself and looking at papers that have referenced it I find they were mostly looking at ferrocenes or ruthenocenes. Can anyone provide any useful information, and perhaps add to the article if there is content and sources to justify any such additions? Thanks, EdChem (talk) 15:46, 2 August 2010 (UTC)

Have now obtained the paper and included it in th article. This is the only topic of medical applications I have located. This material seems to me to be marginal relevance for an article; I added it because there seems little else to say about applications. EdChem (talk) 15:53, 9 September 2010 (UTC)

Cyclopentadienyls

Are those parallel, or antiparallel? Because that diagram sure looks like they're antiparallel. DS (talk) 18:00, 14 August 2010 (UTC)

In metallocenes, there is generally free rotation of the cyclopentadienyl moieties about the ring-metal-ring axis. Consequently, both staggered and eclipsed conformations are present and rapidly interconverting in most circumstances. The typical practice is to describe the conformation by the one present in the solid state, usually as established by X-ray crystallography. This is the reason that rhodocene (like ferrocene) is drawn in a staggered conformation whilst ruthenocene is drawn in an eclipsed conformation. The term 'parallel' is thus used to describe the planes in which the cyclopentadienyl ligands are present. 'Antiparallel' is used in chemistry for discussing spin states of electrons, where the distinction between it and parallel is important, but I wouldn't use it to describe ligand orientations in a situation such as this. Having said that, I am willing to stand corrected if others disagree with me. Regards, EdChem (talk) 02:45, 15 August 2010 (UTC)

I was thinking more of the term's use in an oligopeptide context, actually. But you're right - here they're freely interconvertible, and there's no substituents to force a stereoisomerism, so 'parallel' it is. DS (talk) 01:17, 26 August 2010 (UTC)

GA Review

This review is transcluded from Talk:Rhodocene/GA1. The edit link for this section can be used to add comments to the review.

Reviewer: Canada Hky (talk) 05:42, 6 September 2010 (UTC)

Quick fail criteria

No issues with these criteria, so I will continue with a full review below.

Good article review

GA review (see here for criteria)

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Taking a step into my work world to review this article, rather than the sports articles I usually review on my off hours. This is a quick, interesting read that is fairly close to GA criteria.

1. It is reasonably well written.

   a (prose): b (MoS for lead, layout, word choice, fiction, and lists):

   Just a few notes here:

• Rather than a parenthetical reference to the 18 electron rule (oh, how that brings back memories), a quick explanation would be helpful here. Something like "18 electron organometallic complexes are stable, and rhodocene with its 19 valence electrons is highly reactive...."
• Numbers and units should have non-breaking spaces ( ) inserted.

1. It is factually accurate and verifiable.

   a (references): b (citations to reliable sources): c (OR):

   All look good.

2. It is broad in its coverage.

   a (major aspects): b (focused):

   Possibly a brief mention on applications, or the lack thereof, just for completeness sake.

3. It follows the neutral point of view policy.

   Fair representation without bias:

   No problems here.

4. It is stable.

   No edit wars, etc.:

   No edit wars here.

5. It is illustrated by images, where possible and appropriate.

   a (images are tagged and non-free images have fair use rationales): b (appropriate use with suitable captions):

   No issues here.

6. Overall:

   Pass/Fail:

   These issues are quite minor, thus I will place it on hold

Additional comments

It is a well-written article, but is missing some essential parts (point 2. above), namely applications and health issues (history is somewhat covered in "Synthesis" but could be expanded). Please add whatever reliable material is available on that. Those parts will also make the article more accessible to a general reader - the article is rather technical now. Also, would it be possible to add basic information to the chembox, such as appearance, density, solubility, melting/boiling points, etc? Materialscientist (talk) 05:57, 6 September 2010 (UTC)

Yes, I had a similar concern regarding the breadth of coverage, particularly in relation to applications (if any), as well as the history of discovery and study of the compound. There is a little bit of information about the history in the "Synthesis" section, but there is probably more to say (maybe even a separate "History" section?). The lead also feels a bit short and a bit too technical as well. Perhaps a few sentences aimed at the lay reader could be added there. Nsk92 (talk) 06:14, 6 September 2010 (UTC)

Thank you for creating the "History" section. Regarding "The discovery of ferrocene and its "remarkable stability" in 1951...": Perhaps expand this bit a little, explaining the discovery by whom and under what circumstances (during the study of something or other). Nsk92 (talk) 12:16, 12 September 2010 (UTC)

Thanks... it's a work in progress!  :) EdChem (talk) 12:52, 12 September 2010 (UTC)

Response from Nominator

Firstly, thank you to all three reviewers for their comments and suggestions. I have made the following changes:

• I have re-written the lede to include more content, and to reflect the historical context explained in the new 'History' section
• I have added a 'History' section, expanding on the context of the cobalticinium / rhodicinium work in light of ferrocene, and noting the contributions particularly of Fischer and Wilkinson. I have also referenced and linked to their 1973 Nobel Prize for sandwich compounds.
• I have expanded the structure section to better introduce the 18-electron rule.
• I have added a section on a biomedical application involving a radioactive ruthenocenyl-haloperidol compound that beta-decays to the rhodocenyl-haloperidol compound that then oxidises to the rhodicinium-haloperidol.
• I am unaware of any other medical / technological application, but would be happy to add more if anyone can direct me towards reliable sources that I have missed
• I am also unaware of any data on health consequences of ingestion - again, happy to add if anyone can find references, I can get the sources and add the data
• I have no information to add to the infobox... likely, MP, BP, etc are unknown given the dimerisation of rhodocene and its rapid protonation in solution. The 1953 JACS paper does given the colours of solutions of several salts and elemental analysis data, but not other data on those compounds - not sure if any of that is useful
• I have added & nbsp ; everywhere I think I am supposed to... happy to be corrected
• As far as "too technical" goes, I recognise that I have troubles here, and I hope I am improving. Any further suggestions welcomed, or if anyone knows of other editor(s) with whom I might collaborate who could help in this regrad
• I am going to post to the talk pages of each reviewer to advise that I have made changes, and to ask for further input. Sorry if this is the incorrect protocol - this is my first article from scratch and my first GA nomination, so please excuse any ignorance. Thanks, EdChem (talk) 07:36, 13 September 2010 (UTC)

I am impressed with how far you have brought the article based on the guidance offered here. I will have to give it a thorough read over, and I will wait for input from the other reviewers, but I think we are well on the way to making this a good article. Canada Hky (talk) 19:48, 13 September 2010 (UTC)

I think everyone has had an opportunity to say anything they might have wanted to say, and I believe most of the concerns have been addressed. I'm going to promote Rhodocene to GA. Canada Hky (talk) 23:36, 22 September 2010 (UTC)

Thank you to Canada Hky for the review work, and to everyone else who provided input. I am gratified that the article has been judged as GA-standard.  :) EdChem (talk) 07:47, 23 September 2010 (UTC)

History section

Rhodocene#History is very well written but most of it is not about rhodocene!

The first two paragraphs belong at Organometallic chemistry#History, Ferrocene#History or perhaps Metallocene. These articles could be linked to, but there is no need to repeat the history of organometallic chemistry and of metallocenes in each and every article about a metallocene. The content in these first two paragraphs should be moved to the articles mentioned and merged with the existing content there.

Similarly, the lead (or lede) doesn't need such an in-depth discussion of how organometallic chemistry developed before rhodocene was discovered. It can simply say that interest in ferrocene (link to Ferrocene#History) led chemists to try different transition metals, and rhodocenium was discovered.

Ben (talk) 17:33, 6 February 2011 (UTC)

Ben, just fyi, this content has been added in response to comments / requests at the on-going FAC into the article. EdChem (talk) 17:39, 6 February 2011 (UTC)

Fair enough. Sounds like the FA criteria are somewhat dubious if they don't allow you refer readers to a separate article for the deep background.

Love the article though, it's great.

Ben (talk) 23:15, 6 February 2011 (UTC)

Thanks. The problematic criterion is: "Introductory language in the lead and initial sections of the article should be written in plain terms and concepts that can be understood by any literate reader of Wikipedia without any knowledge in the given field before advancing to more detailed explanations of the topic." For organometallic chemistry, this is a major (frankly, impossible) challenge, but I do think the present article is much more understandable (stand alone) for non-chemists with the background spelled out. I agree, though, that having such discussion in every metallocene article would be absurd, so there is a tension here that would take a large community discussion to hope to resolve. In the meantime, if you wanted to stop by the FAC and comment or even express support or opposition for the nomination for FA-status, that would be most welcome. EdChem (talk) 23:25, 6 February 2011 (UTC)

Lead difficulty

Congrats on your FA. Also congrats on the article itself and especially all the work in drawing structural formulas and orbitals and the like.

While getting into the meat of this topic, requires chemical undeerstanding, I disagree that it's impossible to write at least the lead in a more acessible manner. This article lead actually seems a little tougher than Greenwood and Earnshaw, for example. And that is really targetted at inorganic chemists as an audience.

I think if you did the following, the lead would be more accessible:

• Cut it in half, textwise. I didn't think five paras were even allowed. And yours are a little long. The nutshell of rhodocene is that it's a metal atom sandwhiched between two ringed organic molecules. It's the same thing as ferrocene, which is the most famous sandwich molecule, but swap ou the iron for rhodium. It's got a color. The guy who made it got a Nobel prize. Etc. Realize people are going to look at your lead and give up on even getting their arm around the key aspects of the topic. And it's not needed. It IS possible to write a simple executive summary (maybe containing less detail on the chemistry, but fine) that gives a businessman what he needs to know to have a "feel" for this molecule. Think more basic science article, less "abstract of a review article in the literature".
• Cut the evolution of organometallics as a field within the lead. I think in article discussion of some of the field overall, might be useful, but even the English major businessman recognizes it as digression within the lead. Mentioning ferrocene is fine, though.
• Cut as many chemical formulas as possible from the lead. Really other than the formula for rhodocene itself, do we need the others? In a lead that is supposed to be an easier read for non-chemists? Like ferrocene: showing the formula for that in lead is just cruft, when we already describe in text that rhodo and ferro are analogues (plus we have the structural diaram of rhodo to the right). Not sure we need more formulas for the salts and such (in the lead, fine in article). I think even I technicaly trained, grasp the stuff faster, with less of the chemical formulas shown.
• Cut a lot of the blue-linking in lead (do more in the text). Blue is one more thing that slows people down text-wise. Also, people have learned that there is a (bad) tendancy for science writers on Wiki to "define by blue link" and also to write articles that expect people to learn the whole terminology of their field, and basically "have to read 20 articles to understand one". So unfortunately people have the reaction of hesitation rather than joy when they see a lot of blue in a Wiki article. Other than ferrocene and Wilkinson, what else really needs to be blue-linked in lead? Grignard doesn't since it shouldn't be in your lead anyhow (it's basic enough to the story, but is too technical a term, to use as such). Analagous is a junk link (for the lead). The reader just understanding a dictionary definition of the word does fine. If you feel the need to make that link do it in article.
• The last two paras on applications would be both tighter and simpler if you made them into 2-3 sentences. Something along the line of "Rhodocene has been looked at for a medical blabla. Also 4-membered rhodocene has been studied for electronics nd catalysis. Basic understanding of bonding is the primary reason for studying rhodocene, more than immediate applications." For instance, even a non-technical reader will recognize the "the applications of rhodium compounds in medicine[18]" as not enough on topic for a lead. (The rest of the sentence is fine.) And it's fine if in article, you mention that the medical application of rhodocene was studied as part of looking at rhodium in general. But tighter for the lead.

P.s. Please don't take any of this as aggressive. I honestly give you props for all the work here. It's your baby! I just think the reader misses out by not having an easier lead.

TCO (talk) 15:46, 9 February 2011 (UTC)

Hi TCO... thanks for your comments. I don't see them as aggressive, and I don't own the article. I have initiated a discussion at the FA contributions talk page about how to reconcile FA requirements with comments such as yours and Ben's (above). The discussion is here and I invite you to participate. I realise that this does not cover all of the points that you have raised, but I see it as an important part of the issues to be considered. EdChem (talk) 01:50, 12 February 2011 (UTC)

I just saw this thread. I can't agree enough. I know diddly squat about chemistry, but I know Wikipedia, I know FAs and I know how to edit. Even the opening paragraph is ridiculously inaccessible. Why link to Gas phase, which leads to a dreadfully dense and impenetrable redirect (that redirect should have been picked up at FAC) instead of just writing that it can be detectable when it's a gas or when it's frozen? Then use the body copy to pile on the science jargon and data. Why the strange wording "It is considered an organometallic compound "? (my emphasis). Why not just say it is one? You're implying it might not be one. If that's the case, and it's contentious, say so. At room temperature, is it a solid? liquid? gas? You say what it is at "elevated" temperatures (not specified) but not at any other temperatures. Really, I can't believe this slipped through FAC. By comparison, 0.999..., which is about another scientific topic I don't understand, was a pleasure, with a Lead that introduced the subject gently and comprehensibly. --Dweller (talk) 21:43, 14 February 2011 (UTC)

Is it necessary to include the formulae in the lead? Could we say "ferrocene, the iron analogue of rhodocene" or "Organometallic chemistry first came to prominence with the discovery Zeise's salt, a platinum-containing organic chemical" or something like that?

Similarly, while Dweller's simplification to "detectable when it's a gas or when it's frozen" is okay, I don't think that specifying the temperatures at which this takes place is necessary for the lead.

(Ed—I do think this is a cool molecule. It's not surprising that you find it interesting, and I'm glad that you wrote this article.) WhatamIdoing (talk) 00:49, 15 February 2011 (UTC)

Proposal for a new lead

In an attempt to move this forward, I've chopped out some of the technical stuff from the lead and offer it here for your perusal. Ed, please indicate if I've removed anything you think is essential, and other readers, please suggest other simplications,/text alternations that will help to make this lead accessible to all. (I've removed the citations for ease of editing, they can go back in later) Sasata (talk) 15:18, 15 February 2011 (UTC)

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Rhodocene, formally known as bis(η⁵-cyclopentadienyl)rhodium(II), is a chemical compound with the condensed structural formula [Rh(C₅H₅)₂]. Each molecule contains an atom of rhodium, a transition metal, bound between two planar systems of five carbon atoms known as cyclopentadienyl rings. It is an organometallic compound because the rhodium – carbon bonds are covalent in nature. Rhodocene has a sandwich molecular structure and it is an example of a metallocene, the most famous of which is ferrocene. The [Rh(C₅H₅)₂] radical can exist as a gas or a xxxxid, depending on its temperature. At room temperature, pairs of these radicals combine to form a more stable dimer with diamagnetic properties.

Interest in the field of organometallic chemistry was piqued in the 1950s following the discovery of ferrocene, which was found to have unusually high stability. Soon after, analogous chemical structures with similarly high stability were reported, including cations of rhodocene and cobaltocene. Organometallic species such as these were of great interest because bonding models of the time were unable to explain their formation, let alone their stability. Aqueous solutions of the salt rhodocenium perchlorate undergo one-electron reduction under polarographic conditions to form the neutral rhodocene species, but this is too unstable to be isolated. Work on sandwich compounds, including the rhodocenium / rhodocene system, earned Geoffrey Wilkinson and Ernst Otto Fischer the 1973 Nobel Prize for Chemistry.

Owing to their stability and relative ease of preparation, rhodocenium salts are the usual starting material for preparing rhodocene and substituted rhodocenes. The original synthesis made use of a Grignard-generated carbanion and tris(acetylacetonato)rhodium(III) and numerous other approaches have since been reported, including gas-phase redox transmetalation and using half-sandwich precursors. Octaphenylrhodocene was the first substituted rhodocene to be isolated at room temperature, even though it decomposes rapidly in air. X-ray crystallography confirmed that octaphenylrhodocene has a sandwich structure with a staggered conformation. Unlike cobaltocene, which has become a useful one-electron reducing agent in the research laboratory setting, no rhodocene derivative yet discovered has sufficient stability for such applications.

A ruthenocenyl – haloperidol radiopharmaceutical has been developed that binds strongly to tissues in the lungs but not the brains of mice and rats. Beta-decay of the metal centre in this substance produces a metastable radioactive isotope that may have biomedical applications. Like other rhodocene derivatives, the compound is unstable and rapidly oxidises to a more stable cationic rhodocenium – haloperidol species. A more recent use of rhodocene derivatives has been the synthesis of linked metallocenes, which are interesting for the insights they provide into metal – metal interactions. Such materials could find applications in molecular electronics and the exploration of the boundary between heterogeneous and homogeneous catalysis.

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I was having a go at this offline and have pasted in my working version above (and then reverted). I am not a specialist in this area, but also not frightened by the technical language. I just think the lead section needs to be written with the lay reader in mind (ideally the same approach would be adopted further into the article to the extent feasible, particularly in the introductory section on history).

See the difference between our attempts in this diff. I think the right approach must be:

• an introductory paragraph saying what it is
• one paragraph on the history leading to its discovery and the Nobel prize
• one paragraph on how it can be made
• one paragraph on how it might be used

I would go for a rather more radical shortening of the last two paragraphs than Sasata did - indeed, perhaps they could be merged - but would leave in more of the history (essentially the first two sentences of the second paragraph). Looking back, perhaps it would be more consistent to shorten the second paragraph too. I have also tried to simplify the language a bit more for the non-specialist. If this is unwelcome, then feel free to revert. -- Testing times (talk) 20:39, 15 February 2011 (UTC)

• Hi, thanks for offering an alternate version; I'm putting it below so we can see it better. Hopefully other will offer their opinions too. Sasata (talk) 02:05, 16 February 2011 (UTC)

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Rhodocene, formally known as bis(η⁵-cyclopentadienyl)rhodium(II), is a chemical compound with the condensed structural formula [Rh(C₅H₅)₂]. Each molecule of rhodocene contains an atom of rhodium, a transition metal, linked by covalent bonds to two coplanar systems of five carbon atoms, known as cyclopentadienyl rings. It is considered an organometallic compound and described as having a sandwich molecular structure. It is an example of a metallocene, the most famous of which is ferrocene - the iron analogue of rhodocene. [At atmospheric pressure?], the rhodocene radical can be detected as a gas [at elevated temperatures [define - above 200C? 500C? 1,000C? more?] or [as a solid?] when cooled to the temperature of liquid nitrogen (−196 °C). At room temperature, pairs of rhodocene radicals link to form a more stable, diamagnetic dimer, which is a yellow solid.

Organometallic chemistry first came to prominence with the discovery in the 1820s of a platinum compound now known as Zeise's salt. By the 1880s, Ludwig Mond had developed an industrial process for purification of nickel using the organometallic compound nickel tetracarbonyl. Interest in the field greatly expanded in the 1950s following the discovery of ferrocene - the first metallocene - which was found to have unusually high stability. Soon after, analogous chemical structures with similarly high stability were reported, including ions of rhodocene with a single positive electric charge,^{[Note 1]} and cobaltocene. Organometallic compounds were of great interest at the time because contemporary models of chemical bonds were unable to explain their formation, let alone their stability. Work on sandwich compounds - including the rhodocenium [what is this?] / rhodocene system - earned Geoffrey Wilkinson and Ernst Otto Fischer the 1973 Nobel Prize for Chemistry.

Rhodocene was first created in the laboratory using a Grignard-generated carbanion and tris(acetylacetonato)rhodium(III). Several other approaches have since been reported, including gas-phase redox transmetalation and using half-sandwich precursors. Owing to their stability and relative ease of preparation, rhodocenium salts are the usual starting material for preparing rhodocene and substituted rhodocenes.

Biomedical researchers have examined the applications of rhodium compounds and their derivatives in medicine and reported one potential application for a rhodocene derivative as a radiopharmaceutical to treat small cancers. Rhodocene derivatives can also be used to synthesise of other metallocenes, which can provide interesting insights into metal–metal interactions, and could find applications in molecular electronics and research into the mechanisms of catalysis. The value of rhodocenes may not be in their direct use in applications, but instead in the insights they provide into the bonding and dynamics of novel chemical systems.

References

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Thanks to both editors offering suggested re-drafts. I have yet to look at either in detail, but am grateful for the input / suggestions. I was planning to try a re-write as well, but I want to emphasise my belief that consensus should determine which draft (or combination) is most appropriate. I know we all know but I want to state definitively that I do not WP:OWN the article, and that any and all improvements and talk page suggestions are welcome. One important reminder coming out of the WT:FAC discussion is that FA's remain works in progress, just as any other article, so normal collaborative editing processes apply. I'll comment more later - just wanted people to know I am aware of suggestions and coments having been made. EdChem (talk) 03:52, 16 February 2011 (UTC)
I offer here a redraft of the first three paragraphs. I suspect others will do better than I combining and shortening the fourth and fifth paragraphs. EdChem (talk) 12:41, 16 February 2011 (UTC)

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Rhodocene, formally known as bis(η⁵-cyclopentadienyl)rhodium(II), is a chemical compound with the formula [Rh(C₅H₅)₂]. Each molecule contains an atom of rhodium, a transition metal, bound between two planar systems of five carbon atoms known as cyclopentadienyl rings, an arrangement typical of sandwich compounds. It is an organometallic compound as it has covalent rhodium–carbon bonds. The [Rh(C₅H₅)₂] radical is found above 150 °C in the gas state or when trapped by cooling to liquid nitrogen temperatures (−196 °C). At room temperature, pairs of these radicals combine to form a dimer, [Rh(C₅H₅)₂]₂, with two of the cyclopentadienyl rings joined.

The history of organometallic chemistry includes the 19th century discoveries of Zeise's salt and Ludwig Mond's discovery of nickel tetracarbonyl. These compounds posed a challenge to chemists as they did not fit with chemical bonding models as they were then understood. A further challenge arose with the discovery of ferrocene, the iron analogue of rhodocene and the first of the class of compounds now known as metallocenes. Ferrocene was found to be unusually chemically stable, as were analogous chemical structures including rhodocenium, the unipositive cation of rhodocene^{[Note 1]} and its cobalt and iridium counterparts. The study of organometallic species including these ultimately led to the development of new bonding models that explained both their formation and their stability. Work on sandwich compounds, including the rhodocenium / rhodocene system, earned Geoffrey Wilkinson and Ernst Otto Fischer the 1973 Nobel Prize for Chemistry.

Owing to their stability and relative ease of preparation, rhodocenium salts are the usual starting material for preparing rhodocene and substituted rhodocenes, all of which are unstable. The original synthesis used a Grignard-generated carbanion and tris(acetylacetonato)rhodium(III); numerous other approaches have since been reported, including gas-phase redox transmetalation and using half-sandwich precursors. Octaphenylrhodocene was the first substituted rhodocene to be isolated at room temperature, though even it decomposes rapidly in air. X-ray crystallography confirmed that octaphenylrhodocene has a sandwich structure with a staggered conformation. Unlike cobaltocene, which has become a useful one-electron reducing agent in the research laboratory setting, no rhodocene derivative yet discovered has sufficient stability for such applications.

References

Some issues on parag 1:

• Why explain what rhodium is, but not carbon? Drop "a transition metal" from the Lead as excessive detail.
• Gas state redirects to gas. Redirects breach FA quality - and why not just say "gas", a term everyone is familiar with?
• Are you saying that it only exists at high and low temperatures, but at room temperature, Rhodocene, erm, isn't Rhodocene, or are you saying it's only detectable at extremes of temperature?
• It should be possible for the Lead to be mostly or entirely citation-free, which aids reading, as all facts in the Lead should be in the body of the article.

Back later. --Dweller (talk) 12:59, 16 February 2011 (UTC)

Dweller, thanks for your comments - responses below. I look forward to future input.  :)

1. Dropping "a transition metal" is fine with me, but to answer your question, I expect the "average" reader to have heard of carbon and hydrogen but not of rhodium so I provided some additional detail on rhodium. Alternative suggestions as to how to offer some support in this area for readers (if appropriate) are welcome.
2. Ok, but how? Changing "is found above 150 °C in the gas state" to "in gas" is ungrammatic. Options like "in gas state" and "in gas phase" are ruled out by earlier suggestions. An alternative wording would be welcome.
3. I'm saying it has a monomer and dimer form and the dimer form predominates at room temperature. It can be detected at room temperature when generated electrochemically, but rapidly reacts either back to the dimer or to a derivative. In gaseous state where molecules are widely separated the monomer form is much more stabilised, as is the case when frozen out in liquid nitrogen. Whether rhodocene "only exists" at high and low temperatures is kind of a matter of definition. If rhodocene refers only to the monomer then the answer is sort-of yes (sort-of because it has a very short lifetime at room temperature but it can be formed); if it refers to the system including both the monomer and dimer then the answer is no. In systems which spontaneously interconvert between differing forms trying to describe only one of those forms is problematic.
4. There is no cite in the lede that is not repeated in the body so theoretically they could all be removed, but my understanding was the decision to include or not was stylistic. If the consensus is to not reference the lede I'll accept that, but my personal preference (for what that is worth) is that referencing the lede is desirable.

EdChem (talk) 13:29, 16 February 2011 (UTC)

• Comments Sasata (talk) 20:57, 16 February 2011 (UTC)
• does atom really need to be linked? I would think the average 13-year-old would know that word. I think I feel the same about "molecule".
• is it necessary to include the formula of the dimer?
• since there's a lot of discussion about chemical stability, perhaps that should be linked?
• regarding citations in the lead, I prefer them without, but yeah, its a personal preference
• regarding the gas phase, how about leaving it out? Thus, "The [Rh(C5H5)2] radical can be detected above 150 °C or when trapped by cooling…"
• would it be worthwhile to gloss a definition of octaphenylrhodocene? e.g. "Octaphenylrhodocene (a derivative with eight phenyl groups attached) was the first substituted rhodocene to be isolated at room temperature…"
• otherwise, it looks fine to me, but then again, I understand the words :) At some point, it might be a good idea to add a link to the FAC talk page and invite non-experts to critique before replacing it "officially". Sasata (talk) 20:57, 16 February 2011 (UTC)
  • Thanks for the suggestions / comments, Sasata. My thoughts...

1. Unlinking atom and molecule is fine with me.
2. I gave a formula for the dimer because I thought readers might find the term unfamiliar, but if consensus is that the explanation is sufficiently clear then the formula can go
3. Good ideas on linking chemical stability, defining octaphenyl and removing gas phase entirely - such a simple solution! :)
4. Yes, inviting comment from FAC is probably necessary - I just fear getting further trampled. :(

EdChem (talk) 23:02, 16 February 2011 (UTC)

Working version combining various proposals

Rhodocene, formally known as bis(η⁵-cyclopentadienyl)rhodium(II), is a chemical compound with the formula [Rh(C₅H₅)₂]. Each molecule contains an atom of rhodium bound between two planar systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has covalent rhodium–carbon bonds. The [Rh(C₅H₅)₂] radical is found above 150 °C or when trapped by cooling to liquid nitrogen temperatures (−196 °C). At room temperature, pairs of these radicals combine to form a dimer, a yellow solid in which two of these cyclopentadienyl rings are joined.

The history of organometallic chemistry includes the 19th century discoveries of Zeise's salt and Ludwig Mond's discovery of nickel tetracarbonyl. These compounds posed a challenge to chemists as they did not fit with chemical bonding models as they were then understood. A further challenge arose with the discovery of ferrocene, the iron analogue of rhodocene and the first of the class of compounds now known as metallocenes. Ferrocene was found to be unusually chemically stable, as were analogous chemical structures including rhodocenium, the unipositive cation of rhodocene^{[Note 1]} and its cobalt and iridium counterparts. The study of organometallic species including these ultimately led to the development of new bonding models that explained both their formation and their stability. Work on sandwich compounds, including the rhodocenium / rhodocene system, earned Geoffrey Wilkinson and Ernst Otto Fischer the 1973 Nobel Prize for Chemistry.

Owing to their stability and relative ease of preparation, rhodocenium salts are the usual starting material for preparing rhodocene and substituted rhodocenes, all of which are unstable. The original synthesis used a cyclopentadienyl anion and tris(acetylacetonato)rhodium(III); numerous other approaches have since been reported, including gas-phase redox transmetalation and using half-sandwich precursors. Octaphenylrhodocene (a derivative with eight phenyl groups attached) was the first substituted rhodocene to be isolated at room temperature, though even it decomposes rapidly in air. X-ray crystallography confirmed that octaphenylrhodocene has a sandwich structure with a staggered conformation. Unlike cobaltocene, which has become a useful one-electron reducing agent in the research laboratory setting, no rhodocene derivative yet discovered has sufficient stability for such applications.

Biomedical researchers have examined the applications of rhodium compounds and their derivatives in medicine and reported one potential application for a rhodocene derivative as a radiopharmaceutical to treat small cancers. Rhodocene derivatives are also used to synthesise linked metallocenes so that metal–metal interactions can be studied; potential applications of these derivatives include molecular electronics and research into the mechanisms of catalysis. The value of rhodocenes tend to be in the insights they provide into the bonding and dynamics of novel chemical systems, rather than their direct use in applications.

References

I will give it a wack when sober. Happy to see us all playing together in the sandbox. My contribution will be even less sciencey, but I think fine for the lead (body still has all the science). Anyhow, at least I won't do it in a lippogram. Toodles.TCO (talk) 03:14, 17 February 2011 (UTC) P.s. don't let the wiki get to ya.  ;)

I have instituted the new lede. Others may, as always, alter if they wish. Maybe it's better. EdChem (talk) 13:13, 22 February 2011 (UTC)

Formula

The lead says that the formula is [Rh(C5H5)2] while the infobox says C₁₀H₁₀Rh. Can someone clarify this? --89.76.224.253 (talk) 10:48, 28 March 2011 (UTC)

Thanks, they are the same formula algebraically - the lead formula just shows the two groups attached to the metal explicitly, while the infobox gives the simplest formula (2 x 5 = 10 for C and H both). Ruhrfisch _><>°^° 10:59, 28 March 2011 (UTC)

Ruthenocenyl–haloperidol

Could someone please provide the structural formula of ruthenocenyl–haloperidol under the haloperidol formula (image already provided) so that they may be compared? Thanks a lot. I'd also like to know the pros and cons of using ruthenocenyl–haloperidol in medicine (if this is already stated, it should be made more explicit). --Eleassar ^{my talk} 19:35, 28 March 2011 (UTC)

I do not know the specifics, but since the Ru takes the place of the Fe, it should be (C₅H₅)Ru(C₅H₄)–C(=O)–(CH₂)₃–N(CH₂CH₂)₂C(OH)–C₆H₄Cl. For more details, please see reference number 19: Wenzel, M.; Wu, Y. (1988). "Ferrocen-, Ruthenocen-bzw. Rhodocen-analoga von Haloperidol Synthese und Organverteilung nach Markierung mit 103Ru-bzw. 103mRh" (in German). Int. J. Rad. Appl. Instrum. A. 39 (12): 1237–1241. doi:10.1016/0883-2889(88)90106-2. PMID 2851003. Ruhrfisch _><>°^° 21:24, 28 March 2011 (UTC)

TFA image question

At the moment (some hours before Rhodocene goes TFA), Wikipedia:Main Page/Errors § Tomorrow's FA has a post by Dying that most likely belongs here. I'll copy/paste it here for talkflow & history saving reasons. It has my earlier reply too. -DePiep (talk) 20:05, 2 November 2021 (UTC)

* apologies in advance, both for bringing up an issue more technical than usual, and if i have misinterpreted something below. i cannot claim expertise on the subject matter; most of what i know of organometallic chemistry i learned while reading the associated article.

i am wondering if it is appropriate to use the image in the blurb as is. from what i understand, the model appears to show rhodocene in an eclipsed conformation, as opposed to a staggered conformation, as seen in this model of ferrocene, another metallocene containing two cyclopentadienyl rings in a sandwich structure. (very roughly, the difference is similar to the difference between hand steepling and hand clasping.) the nominator, EdChem, has previously mentioned on the article's talk page that metallocenes are typically described by its conformation in the solid state, which is why rhodocene and ferrocene tend to be illustrated with a staggered conformation, while ruthenocene tends to not be.

from what i understand from the article, although rhodocene molecules may rapidly convert between the two conformations, the monomeric form of the compound in its solid state exhibits a staggered conformation, so i worry that the current blurb may be misleading for those who are familiar with the standard of presenting metallocenes in their solid state conformations. (a similar issue appears to have also been brought up as the last point in the article's review.) the image in question appears to have been added comparatively recently, years after the article's promotion to featured status, so i am assuming that EdChem has not had the opportunity to review it.

if my worry is not unfounded, offhand, i can think of two solutions. the current image may be replaced by this one illustrating rhodocene in a staggered conformation, as used in an earlier blurb. (note that this older image appears to be a transparent png, so it may be a good idea to remove the transparency beforehand to avoid an issue previously reported with such images on the main page.) alternatively, the caption may be changed to "Structure of rhodocene in an eclipsed conformation", which may more clearly suggest that the eclipsed conformation is not the conformation usually exhibited by rhodocene in a solid state. dying (talk) 17:31, 2 November 2021 (UTC)

@Dying: For starters, to get your point: you write about the current blurb image being eclipsed conformation not staggered conformation. Is that a chemical issue (pertaining to the molecule itself), or a presentation issue (i.e., the image could be improved)? (interested chem people could check the "3D model (JSmol)" interactive entry in the {{Chembox}}. Caveat: since ferrocene is mentioned in relation to this: I remember the |Jmol= did not function with ferrocene SMILES inpuit - see f. Chembox code ;-) ).

Apart from this, AFAIU[nderstand], in any case the question & improvement should be in the article itself. -DePiep (talk) 19:56, 2 November 2021 (UTC)

Why monomeric rhodocene is unstable?

This issue is fully explained in Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8., p. 939. The unpaired electron in RhCp₂ occupies an antibonding orbital; its removal produces the stable cation [RhCp₂]⁺ which has the same electronic structure as ferrocene. Given that the monomer is stable only at temperatures well below 0 C, the title of this article is seriously misleading. Petergans (talk) 10:45, 3 November 2021 (UTC)

I wonder what makes monomeric rhodocene that bit less stable than monomeric cobaltocene, then. Double sharp (talk) 20:37, 24 November 2021 (UTC)