{"id":10733,"date":"2013-07-03T11:19:07","date_gmt":"2013-07-03T10:19:07","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=10733"},"modified":"2013-07-03T14:23:15","modified_gmt":"2013-07-03T13:23:15","slug":"is-dicarbon-c2-a-molecule-of-chemical-interest","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733","title":{"rendered":"Is dicarbon (C2) a molecule of chemical interest?"},"content":{"rendered":"
\n

C2<\/sub>\u00a0(dicarbon) is certainly interesting<\/a> from a theoretical point of view. Whether or not it can be described as having a quadruple bond<\/em> has induced much passionate discussion[1]<\/a><\/span>,[2]<\/a><\/span>,[3]<\/a><\/span>,[4]<\/a><\/span>. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly reactive species (cyclobutadiene<\/a> is a well-known example) can often be tamed by trapping<\/a> as a ligand coordinated to a metal and so one might speculate upon how C2<\/sub> responds to the proximity of a metal. As is noted here[2]<\/a><\/span>, dicarbon as a ligand has been known a long time as part of what is referred to as carbide chemistry. In this regard it is thought of as the di-anion, C2<\/sub>2-<\/sup> (and isoelectronic therefore with dinitrogen). Thus calcium carbide, but in fact the degree to which the dicarbon can absorb electrons is thought to be wide (as judged by the resulting C-C bond length, see[2]<\/a><\/span>). Here I take a look at just one metal carbide[5]<\/a><\/span> that caught my eye (there are hundreds of others, many no doubt equally interesting!).<\/p>\n

\"dicarbon\"<\/p>\n

One first notices that the standard attempt at a representation above does not do it justice; a Lewis valence bond drawing (in which electrons are accounted by partitioning into bonds) it most certainly is not. Nine carbons and four osmiums have absorbed 21 electrons, donated (formally) from seven lanthanum atoms. But easily discerned is that of the nine carbons, four are dicarbon and five are mono carbon. It is worth exploring the immediate environment of each of these types. The monocarbon is in fact hexa-coordinate<\/a>d by two Os and four La, a form of carbon coordination that was only relatively recently identified.<\/p>\n

\"Click

Click for 3D<\/p><\/div>\n

But the dicarbon unit is if anything even stranger. The C-C bond length is ~1.316\u00c5 (a relatively long distance compared to many carbides) more or less commensurate with a double bond. The carbons are both end-on \u03c3-coordinated and also triply \u03c0-coordinated. with one more metal coordinating in a manner somewhat in-between these two modes. One carbon is 5-coordinate, the other 6-coordinate. The Os-C bond length has a relatively short value of 1.93\u00c5 (the sum of the double bond covalent radii for Os and C is 1.83, the single bond radii 2.04), and so it might be tempting to represent it as Os=C=C.<\/p>\n

\"Click

Click for 3D<\/p><\/div>\n

This one example reminds us that even an element such as carbon, where one might imagine the bonding environments would be well-known, can still reveal unusual behaviours. Taking a look at the histogram below, which indicates C-C lengths in Metal-CC-Metal complexes (where the carbon coordination is restricted to 2) indicates the diversity of behaviour possible with this simple little ligand.<\/p>\n

\"LaOsCC-hist\"<\/p>\n

References<\/h2>\n
  1. S. Shaik, D. Danovich, W. Wu, P. Su, H.S. Rzepa, and P.C. Hiberty, \"Quadruple bonding in C2 and analogous eight-valence electron species\", Nature Chemistry<\/i>, vol. 4, pp. 195-200, 2012. https:\/\/doi.org\/10.1038\/nchem.1263<\/a>\n\n<\/li>\n
  2. S. Shaik, H.S. Rzepa, and R. Hoffmann, \"One Molecule, Two Atoms, Three Views, Four Bonds?\", Angewandte Chemie International Edition<\/i>, vol. 52, pp. 3020-3033, 2013. https:\/\/doi.org\/10.1002\/anie.201208206<\/a>\n\n<\/li>\n
  3. G. Frenking, and M. Hermann, \"Critical Comments on \u201cOne Molecule, Two Atoms, Three Views, Four Bonds?\u201d\", Angewandte Chemie International Edition<\/i>, vol. 52, pp. 5922-5925, 2013. https:\/\/doi.org\/10.1002\/anie.201301485<\/a>\n\n<\/li>\n
  4. D. Danovich, S. Shaik, H.S. Rzepa, and R. Hoffmann, \"A Response to the Critical Comments on \u201cOne Molecule, Two Atoms, Three Views, Four Bonds?\u201d\", Angewandte Chemie International Edition<\/i>, vol. 52, pp. 5926-5928, 2013. https:\/\/doi.org\/10.1002\/anie.201302350<\/a>\n\n<\/li>\n
  5. E. Dashjav, Y. Prots, G. Kreiner, W. Schnelle, F.R. Wagner, and R. Kniep, \"Chemical bonding analysis and properties of La7Os4C9\u2014A new structure type containing C- and C2-units as Os-coordinating ligands\", Journal of Solid State Chemistry<\/i>, vol. 181, pp. 3121-3130, 2008. https:\/\/doi.org\/10.1016\/j.jssc.2008.08.005<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    C2\u00a0(dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion,,,. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly reactive species (cyclobutadiene is a […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[157,1088,1089],"ppma_author":[2661],"class_list":["post-10733","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-metal","tag-metal-coordinating","tag-os-c"],"yoast_head":"\nIs dicarbon (C2) a molecule of chemical interest? - Henry Rzepa's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Is dicarbon (C2) a molecule of chemical interest? - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"C2\u00a0(dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion,,,. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly reactive species (cyclobutadiene is a […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2013-07-03T10:19:07+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2013-07-03T13:23:15+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/07\/dicarbon1.svg\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Is dicarbon (C2) a molecule of chemical interest? - Henry Rzepa's Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10733","og_locale":"en_GB","og_type":"article","og_title":"Is dicarbon (C2) a molecule of chemical interest? - Henry Rzepa's Blog","og_description":"C2\u00a0(dicarbon) is certainly interesting from a theoretical point of view. 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The diatropic\/paratropic inversion.","author":"Henry Rzepa","date":"October 26, 2013","format":false,"excerpt":"The 1H NMR spectrum of an aromatic molecule such as benzene is iconic; one learns that the unusual chemical shift of the protons (~\u03b4 7-8 ppm) is due to their deshielding by a diatropic ring current resulting from the circulation of six aromatic \u03c0-electrons following the H\u00fcckel 4n+2 rule. 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Both compounds exhibit (approximately) linear chains of iodine atoms in their crystal structures, a connection which was discovered\u2026","rel":"","context":"In "Chiroptics"","block_context":{"text":"Chiroptics","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2644"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/10\/Screenshot-925-1024x248.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":14601,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14601","url_meta":{"origin":10733,"position":2},"title":"Yes, no, yes. Computational mechanistic exploration of (nickel-catalysed) cyclopropanation using tetramethylammonium triflate.","author":"Henry Rzepa","date":"October 1, 2015","format":false,"excerpt":"A fascinating re-examination has appeared of a reaction first published in 1960 by Wittig and then repudiated by him in 1964 since it could not be replicated by a later student. According to the new work, the secret to a successful replication\u00a0seems to be\u00a0the presence of traces of a nickel\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":22578,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=22578","url_meta":{"origin":10733,"position":3},"title":"The Willgerodt-Kindler Reaction: mechanistic reality check 2.","author":"Henry Rzepa","date":"August 14, 2020","format":false,"excerpt":"Continuing an exploration of the mechanism of this reaction, an alternative new mechanism was suggested in 1989 (having been first submitted to the journal ten years earlier!). Here the key intermediate proposed is a thiirenium cation (labelled 8 in the article) and labelled\u00a0Int3 below. The model chosen is the same\u2026","rel":"","context":"In "reaction mechanism"","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":13387,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13387","url_meta":{"origin":10733,"position":4},"title":"How-open-is-it?","author":"Henry Rzepa","date":"February 12, 2015","format":false,"excerpt":"The title of this post refers to the site\u00a0http:\/\/howopenisit.org\/\u00a0 which is in effect a license scraper for journal articles. In the past 2-3 years in the UK, we have been able to make use of grants to our university to pay publishers to convert our publications into Open Access (also\u2026","rel":"","context":"In "Chemical IT"","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":17205,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17205","url_meta":{"origin":10733,"position":5},"title":"Molecules of the year? The most polar neutral compound synthesized…","author":"Henry Rzepa","date":"December 18, 2016","format":false,"excerpt":"This, the fourth candidate provided by C&EN for a vote for the molecule of the year\u00a0as discussed here,\u00a0lays claim to the World's most polar neutral molecule (system 1 shown below). Here I explore\u00a0a strategy for extending that record. The claim for 1 (3 in\u00a0) is on the basis of its\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/10733","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=10733"}],"version-history":[{"count":11,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/10733\/revisions"}],"predecessor-version":[{"id":10794,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/10733\/revisions\/10794"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10733"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10733"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10733"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=10733"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}