{"id":25581,"date":"2022-09-15T06:43:28","date_gmt":"2022-09-15T05:43:28","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=25581"},"modified":"2022-09-15T07:51:07","modified_gmt":"2022-09-15T06:51:07","slug":"examples-of-inverted-or-hemispherical-carbon","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=25581","title":{"rendered":"Examples of inverted or hemispherical carbon?"},"content":{"rendered":"
\n

In previously asking what the largest angle subtended at four-coordinate carbon might be<\/a>, I noted that as the angle increases beyond 180\u00b0, the carbon becomes inverted, or hemispherical (all four ligands in one hemisphere). So what does a search for this situation reveal in the CSD? The query can be formulated as below, in which the distance from the centroid of the four ligands to the central carbon is specified to be in e.g.<\/em> the range 0.8 to 1.1\u00c5.\u00a0For tetrahedral carbon surrounded by four carbon ligands, the value would be close to zero, so any value larger than say 0.8\u00c5 is worth inspecting.
\n\"\"<\/p>\n

Many of the 101 hits are false positives for inverted carbon (by inspection),\u00a0but five turn out to be propellanes and eight contain the unusual motif shown below:<\/p>\n

\"\"<\/p>\n

Here I give one example of each. SADHUA[1]<\/a><\/span> is a crystalline [1.1.1]propellane in which the “central” bond length is a normal looking 1.558\u00c5. In fact there is positive (experimental) difference electron density on both “exo” ends of this bond and negative difference density in the “endo” region, suggesting the bond is indeed unusual (FAIR DOI: 10.14469\/hpc\/11159<\/a>).<\/p>\n

\"\"\u00a0<\/p>\n

One example of the other motif is SEWZID[2]<\/a><\/span>, where the four ligands to the inverted carbon comprise two\u00a0C-C bonds and two apparent C-Fe bonds of length 2.04\u00c5. A typical C-Fe bond length is in the region 1.8\u00c5, so these are longish C-Fe bonds. Indeed, their\u00a0Wiberg bond orders emerge as ~0.3, so they would not normally count as a “bond”.\u00a0Nonetheless, they are indexed as such in the\u00a0CSD! This highlights an interesting aspect of how to construct a searchable crystal structure database. You have to make a decision on whether any pair of atoms is “bonded” or not. And the decision for bonds with orders\u00a0<1 can be particularly difficult, especially if calculations of these properties are not part of your assignment toolkit.<\/p>\n

\"\"<\/p>\n

So we might conclude that inverted or hemispherical four-coordinate carbon is a rare beast; all the more surprising that the best known examples, the [1.1.1]-propellanes are so stable! Apart from the metallocarbons, one of which is illustrated above, are there any others?<\/p>\n

References<\/h2>\n
  1. P. Seiler, J. Belzner, U. Bunz, and G. Szeimies, \"Crystal Structure and Electron\u2010Density Distribution of Two [1.1.1] Propellane Derivatives at 81 K\", Helvetica Chimica Acta<\/i>, vol. 71, pp. 2100-2110, 1988. https:\/\/doi.org\/10.1002\/hlca.19880710827<\/a>\n\n<\/li>\n
  2. R. Rumin, F. Petillon, L. Manojlovic-Muir, and K.W. Muir, \"Reactions of di- and polynuclear complexes. 6. Reaction of [(.eta.5-C5H5)(CO)Fe{.mu.-C(CF3)=C(CF3)SMe}2Fe(CO)(.eta.5-C5H5)] with [Fe3(CO)12]. Ligand exchange between metals: synthesis and characterization of di- and trinuclear iron-alkyne complexes. Crystal structure of [{Fe(CO)3}2{.mu.-(CF3)CCC[Fe(.eta.5-C5H5)(CO)2]}]\", Organometallics<\/i>, vol. 9, pp. 944-952, 1990. https:\/\/doi.org\/10.1021\/om00118a008<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    In previously asking what the largest angle subtended at four-coordinate carbon might be, I noted that as the angle increases beyond 180\u00b0, the carbon becomes inverted, or hemispherical (all four ligands in one hemisphere). So what does a search for this situation reveal in the CSD? The query can be formulated as below, in which […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_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}},"categories":[],"tags":[],"ppma_author":[2661],"class_list":["post-25581","post","type-post","status-publish","format-standard","hentry"],"yoast_head":"\nExamples of inverted or hemispherical carbon? - 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=25581\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Examples of inverted or hemispherical carbon? - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"In previously asking what the largest angle subtended at four-coordinate carbon might be, I noted that as the angle increases beyond 180\u00b0, the carbon becomes inverted, or hemispherical (all four ligands in one hemisphere). 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This is characterised by a central carbon with five coordinated ligands. The original suggestion included two astatine atoms as ligands (X=At), but in my post I suggested an alternative\u2026","rel":"","context":"In "Hypervalency"","block_context":{"text":"Hypervalency","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=7"},"img":{"alt_text":"The Sn2 transition state","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2009\/09\/sn2.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":14548,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14548","url_meta":{"origin":25581,"position":1},"title":"Deviations from tetrahedral four-coordinate carbon: a statistical exploration.","author":"Henry Rzepa","date":"September 6, 2015","format":false,"excerpt":"An article entitled \"Four Decades of the Chemistry of Planar Hypercoordinate Compounds\" was recently reviewed by Steve Bacharach on his blog, where you can also see comments. Given the recent crystallographic themes here, I thought I might try a search of the CSD (Cambridge structure database) to see whether anything\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":8048,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8048","url_meta":{"origin":25581,"position":2},"title":"Trimethylenemethane Ruthenium benzene","author":"Henry Rzepa","date":"October 17, 2012","format":false,"excerpt":"Every once in a while, one encounters a molecule which instantly makes an interesting point. Thus Ruthenium is ten electrons short of completing an 18-electron shell, and it can form a complex with benzene on one face and a ligand known as trimethylenemethane on the other. This four-carbon molecule has\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":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/10\/JODLIX.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":14560,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14560","url_meta":{"origin":25581,"position":3},"title":"Deviations from planarity of trigonal carbon and from linearity of digonal carbon.","author":"Henry Rzepa","date":"September 13, 2015","format":false,"excerpt":"Previously, I explored deviation from ideal tetrahedral arrangements of four carbon ligands around a central (sp3) carbon using crystal structures. Now it is the turn of digonal (sp1) and trigonal (sp2) carbons.\u00a0 Firstly, the digonal C\u2261C case. Attached to each carbon of the C\u2261C unit are two saturated carbon ligands;\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":30548,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=30548","url_meta":{"origin":25581,"position":4},"title":"Molecules of the year 2025: Benzene-busting inverted sandwich.","author":"Henry Rzepa","date":"January 1, 2026","format":false,"excerpt":"Sandwich compounds are the colloquial term used for molecules where a metal atom such as an iron dication is \"sandwiched\" between two carbon-based rings as ligands, most commonly cyclopentadienyl anion (the \"bread\") as in e.g. Ferrocene - a molecule first discovered in 1951. An \"inverted\" sandwich is where the carbon\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":17063,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=17063","url_meta":{"origin":25581,"position":5},"title":"The largest C-C-C angle?","author":"Henry Rzepa","date":"November 1, 2016","format":false,"excerpt":"I am now inverting the previous question by asking what is the largest angle subtended at a chain of three connected 4-coordinate carbon atoms? Let's see if further interesting chemistry can be unearthed. Specifying only angles > 130\u00b0, the following distribution is obtained. Note the maximum at ~138\u00b0. This is\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"vajhap","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2016\/10\/VAJHAP.jpg?resize=350%2C200","width":350,"height":200},"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\/25581","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=25581"}],"version-history":[{"count":17,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/25581\/revisions"}],"predecessor-version":[{"id":25610,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/25581\/revisions\/25610"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25581"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25581"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25581"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=25581"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}