{"id":4479,"date":"2011-06-26T18:30:55","date_gmt":"2011-06-26T18:30:55","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=4479"},"modified":"2011-06-27T06:35:38","modified_gmt":"2011-06-27T06:35:38","slug":"hexavalent-carbon-revisited","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=4479","title":{"rendered":"Hexavalent carbon revisited (and undecavalent boron thrown in)."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"4479\">\n<p>A little while ago, <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=878\" target=\"_blank\">I speculated<\/a> (blogs are good for that sort of thing) about hexavalent carbon, and noted how one often needs to make (retrospectively) obvious connections between two different areas of chemistry. That post has attracted a number of comments in the two years its been up, along the lines: <em>what about carboranes?<\/em> So here I have decided to explore that portal into boron chemistry. The starting point is the reported crystal structure of a molecule containing a CH<sub>12<\/sub>B<sub>11<\/sub><sup>&#8211; <\/sup>anion<sup> <\/sup>(DOI:\u00a0<a href=\"http:\/\/dx.doi.org\/10.1021\/ja00201a073\" target=\"_blank\">10.1021\/ja00201a073<\/a>). This differs from the molecule I previously reported in having not so much 5C-C + 1C-H bonds around a single carbon, but instead 5B-C + 1C-H bonds. The basic cluster is much in fashion (as\u00a0B<sub>12<\/sub>Cl<sub>12<\/sub><sup>2-<\/sup>) for its properties as a non-coordinating counterion.<\/p>\n<p><div id=\"attachment_4483\" style=\"width: 229px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-4483\" class=\"size-full wp-image-4483 \" title=\"CB11\" onclick=\"jmolInitialize('..\/Jmol\/',true);jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2011\/06\/VEFMAU-aim.mol;');\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11.jpg\" alt=\"\" width=\"219\" height=\"217\" srcset=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11.jpg 365w, https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11-150x150.jpg 150w, https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11-300x297.jpg 300w\" sizes=\"auto, (max-width: 219px) 100vw, 219px\" \/><p id=\"caption-attachment-4483\" class=\"wp-caption-text\">The CH12B11 (-) anion. AIM analysis. Click for 3D.<\/p><\/div>Above is the QTAIM topological analysis of the electron density (<a href=\"http:\/\/hdl.handle.net\/10042\/to-9118\" target=\"_blank\">B3LYP\/6-311G(d,p) calculation<\/a>) which reveals all 11 borons and the single carbon atom as being surrounded by six bond critical points. ELF tells us how many electrons populate the synaptic basins.<\/p>\n<p><div id=\"attachment_4489\" style=\"width: 341px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-4489\" class=\"size-full wp-image-4489 \" title=\"CB11-elf\" onclick=\"jmolInitialize('..\/Jmol\/',true);jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2011\/06\/CB11.mol;');\" src=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11-elf.jpg\" alt=\"\" width=\"331\" height=\"335\" srcset=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11-elf.jpg 551w, https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2011\/06\/CB11-elf-295x300.jpg 295w\" sizes=\"auto, (max-width: 331px) 100vw, 331px\" \/><p id=\"caption-attachment-4489\" class=\"wp-caption-text\">The CH12B11 (-) anion ELF basins. Click for 3D.<\/p><\/div>This clearly reveals that the bonding to the carbon and all the boron atoms is non-Lewis, <em>i.e.<\/em> that of the six bonds to each of the non-hydrogens, five are not of the Lewis two-electron pair type. The carbon for example is surrounded by five C-B basins, each of 1.02e, with its valence shell occupied by ~7.2e in total. The boron involved in each of the C-B bonds also has five bonds, with basins corresponding to 1.01, 2*0.95 and 2*0.73e. The boron directly opposite the carbon has five basins corresponding to five B-B two-centre bonds of 0.6e each, and a further five basins of 0.3e corresponding to 3-centre BBB bonds (shown as yellow spheres above). Arguably, that particular boron atom has eleven bonds to it!<\/p>\n<p>This molecule reveals quite clearly how sterile the debate is about whether carbon can be hypervalent.\u00a0If the Lewis definition of a bond as an electron pair is removed, then hypervalency exceeding four can easily be obtained. What is certainly sacrosanct is the valence shell octet for carbon (and boron).<\/p>\n<p>Finally, I throw\u00a0<a href=\"http:\/\/hdl.handle.net\/10042\/to-9119\" target=\"_blank\">B<sub>12<\/sub>H<sub>12<\/sub><sup>2-<\/sup><\/a> in. This has the wonderful icosahedral symmetry, and as you might expect, each boron is defined by five two-centre B-B bonds (~0.66e) and five three-centre BBB bonds (~0.24e), as well as a conventional two-electron B-H bond. Each boron is <strong>undecavalent<\/strong>! Not seen that particular valency before!!<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 4479 -->","protected":false},"excerpt":{"rendered":"<p>A little while ago, I speculated (blogs are good for that sort of thing) about hexavalent carbon, and noted how one often needs to make (retrospectively) obvious connections between two different areas of chemistry. That post has attracted a number of comments in the two years its been up, along the lines: what about carboranes? [&hellip;]<\/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":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[7],"tags":[11,571],"ppma_author":[2661],"class_list":["post-4479","post","type-post","status-publish","format-standard","hentry","category-hypervalency","tag-elf","tag-qtaim"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Hexavalent carbon revisited (and undecavalent boron thrown in). - Henry Rzepa&#039;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=4479\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Hexavalent carbon revisited (and undecavalent boron thrown in). - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"A little while ago, I speculated (blogs are good for that sort of thing) about hexavalent carbon, and noted how one often needs to make (retrospectively) obvious connections between two different areas of chemistry. That post has attracted a number of comments in the two years its been up, along the lines: what about carboranes? 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