{"id":13987,"date":"2015-04-26T18:25:23","date_gmt":"2015-04-26T17:25:23","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13987"},"modified":"2023-09-16T18:10:04","modified_gmt":"2023-09-16T17:10:04","slug":"allotropic-halogens","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987","title":{"rendered":"Allotropic halogens."},"content":{"rendered":"
\n

Allotropes<\/a> are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes.<\/p>\n

Firstly, I am not aware of much discussion on the topic. But ClF3<\/sub> is certainly well-known<\/a>, and so it is trivial to suggest BrBr3<\/sub>, i.e.<\/em> Br4<\/sub> as an example of a halogen allotrope. Scifinder for example gives no literature hits on such a substance (either real or as a calculation; it is not always easy nowadays to tell which). So, is it stable? A B3LYP+D3\/6-311++G(2d,2p) calculation reveals a free energy barrier of 17.2 kcal\/mol preventing Br4<\/sub> from dissociating to 2Br2<\/sub>.[1]<\/a><\/span> The reaction however is rather exoenergic, and so to stand any chance of observing Br4<\/sub>, one would probably have to create it at a low temperature. But say -78\u00b0 would probably be low enough to give it a long lifetime; perhaps even 0\u00b0.<\/p>\n

\"Br4c\"<\/a>
\n<\/a>\"Br4\"<\/a><\/p>\n

So how to make it? This is pure speculation, but the red colour of bromine originates from (weak, symmetry forbidden) transitions, with energies calculated (for the 2Br2<\/sub> complex) as\u00a0504, 492nm. Geometry optimisation of the first singlet excited state of 2Br2<\/sub> produces the structure below, not that different from Br4<\/sub>.
\n\"2Br2-excited\"<\/a><\/p>\n

At least from these relatively simple calculations, it does seem as if an allotrope of bromine might be detectable spectroscopically, if not actually isolated as a pure substance.<\/p>\n

\n

Acknowledgments<\/h4>\n

This post has been cross-posted in PDF format at Authorea<\/a>.<\/p>\n

References<\/h2>\n
  1. H.S. Rzepa, \"Br4\", 2015. https:\/\/doi.org\/10.14469\/ch\/191228<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic. But […]<\/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":[1086],"tags":[1435,1436,1440,1432,1395,206,1438,1437,1441,1431,1434,1433,1439,74],"ppma_author":[2661],"class_list":["post-13987","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2","tag-allotropy","tag-bromine","tag-carbon","tag-chemical-elements","tag-chemistry","tag-free-energy-barrier","tag-fullerene","tag-halogen","tag-hypobromite","tag-matter","tag-nonmetals","tag-oxidizing-agents","tag-oxygen","tag-pence"],"yoast_head":"\nAllotropic halogens. - 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=13987\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Allotropic halogens. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic. But […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2015-04-26T17:25:23+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2023-09-16T17:10:04+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif\" \/>\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=\"1 minute\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Allotropic halogens. - 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=13987","og_locale":"en_GB","og_type":"article","og_title":"Allotropic halogens. - Henry Rzepa's Blog","og_description":"Allotropes are differing structural forms of the elements. The best known example is that of carbon, which comes as diamond and graphite, along with the relatively recently discovered fullerenes and now graphenes. Here I ponder whether any of the halogens can have allotropes. Firstly, I am not aware of much discussion on the topic. But […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987","og_site_name":"Henry Rzepa's Blog","article_published_time":"2015-04-26T17:25:23+00:00","article_modified_time":"2023-09-16T17:10:04+00:00","og_image":[{"url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"1 minute"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Allotropic halogens.","datePublished":"2015-04-26T17:25:23+00:00","dateModified":"2023-09-16T17:10:04+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987"},"wordCount":265,"commentCount":9,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif","keywords":["Allotropy","Bromine","Carbon","Chemical elements","Chemistry","free energy barrier","Fullerene","Halogen","Hypobromite","Matter","Nonmetals","Oxidizing agents","Oxygen","pence"],"articleSection":["reaction mechanism"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987","name":"Allotropic halogens. - Henry Rzepa's Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif","datePublished":"2015-04-26T17:25:23+00:00","dateModified":"2023-09-16T17:10:04+00:00","author":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"breadcrumb":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#primaryimage","url":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif","contentUrl":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2015\/04\/Br4c.gif"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13987#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"Allotropic halogens."}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa's Blog","description":"Chemistry with a twist","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Person","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281","name":"Henry Rzepa","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g370be3a7397865e4fd161aefeb0a5a85","url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","caption":"Henry Rzepa"},"description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.","sameAs":["https:\/\/orcid.org\/0000-0002-8635-8390"],"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?author=1"}]}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pDef7-3DB","jetpack-related-posts":[{"id":7601,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7601","url_meta":{"origin":13987,"position":0},"title":"The Sn2 reaction: followed up.","author":"Henry Rzepa","date":"September 12, 2012","format":false,"excerpt":"An obvious issue to follow-up my last post on the (solvated) intrinisic reaction coordinate for the Sn2 reaction is how variation of the halogen (X) impacts upon the nature of the potential. X=FX=Cl X=BrX=I X=FX=Cl X=BrX=I The change in slope of the gradient norm along the IRC is hardly noticeable\u2026","rel":"","context":"In \"potential energy surfaces\"","block_context":{"text":"potential energy surfaces","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=potential-energy-surfaces"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":18993,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=18993","url_meta":{"origin":13987,"position":1},"title":"VSEPR Theory: Octet-busting or not with trimethyl chlorine, ClMe3.","author":"Henry Rzepa","date":"November 12, 2017","format":false,"excerpt":"A few years back, I took a look at the valence-shell electron pair repulsion approach to the geometry of chlorine trifluoride, ClF3 using so-called ELF basins to locate centroids for both the covalent F-Cl bond electrons and the chlorine lone-pair electrons. Whereas the original VSEPR theory talks about five \"electron\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":13488,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=13488","url_meta":{"origin":13987,"position":2},"title":"How many water molecules does it take to ionise HI?","author":"Henry Rzepa","date":"February 28, 2015","format":false,"excerpt":"Why is this post orphaned from the previous? In order to have the opportunity of noting that treating iodine computationally can be a little different from the procedures used for F, Cl and Br. As the nuclear charge increases proceeding down the periodic table, the inner electron shells start becoming\u2026","rel":"","context":"In "General"","block_context":{"text":"General","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":7580,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=7580","url_meta":{"origin":13987,"position":3},"title":"The Sn2 reaction and the anomaly of carbon.","author":"Henry Rzepa","date":"September 6, 2012","format":false,"excerpt":"It was three years ago that I first blogged on the topic of the Sn2 reaction. Matthias Bickelhaupt had suggested that the Sn2 reaction involving displacement at a carbon atom was an anomaly; the true behaviour was in fact exhibited by the next element down in the series, silicon. The\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\/09\/sn2-Na1.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":16497,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16497","url_meta":{"origin":13987,"position":4},"title":"A wider look at chlorine trifluoride: crystal structures and data mining.","author":"Henry Rzepa","date":"June 10, 2016","format":false,"excerpt":"A while ago, I explored how the 3-coordinate halogen compound ClF3\u00a0is conventionally analyzed using\u00a0VSEPR (valence shell electron pair repulsion theory). Here I (belatedly) look at other such tri-coordinate halogen compounds using known structures gleaned from the\u00a0crystal structure database (CSD). The search query specifies\u00a07A as the central atom, defined with just\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":"","src":"","width":0,"height":0},"classes":[]},{"id":2687,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2687","url_meta":{"origin":13987,"position":5},"title":"Hypervalency: Third time lucky?","author":"Henry Rzepa","date":"October 23, 2010","format":false,"excerpt":"One approach to reporting science which is perhaps better suited to the medium of a blog than a conventional journal article is the opportunity to follow ideas in unexpected, even unconventional directions. Thus my third attempt, like a dog worrying a bone, to explore hypervalency. I have, somewhat to my\u2026","rel":"","context":"In "Hypervalency"","block_context":{"text":"Hypervalency","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=7"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/10\/I8.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\/13987","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=13987"}],"version-history":[{"count":6,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/13987\/revisions"}],"predecessor-version":[{"id":26454,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/13987\/revisions\/26454"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=13987"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=13987"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=13987"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=13987"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}