{"id":13158,"date":"2014-12-07T10:28:22","date_gmt":"2014-12-07T10:28:22","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13158"},"modified":"2014-12-07T10:28:22","modified_gmt":"2014-12-07T10:28:22","slug":"halogen-bonds-4-the-strongest-halogen-bond","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2014\/12\/07\/halogen-bonds-4-the-strongest-halogen-bond\/","title":{"rendered":"Halogen bonds 4: The  strongest (?) halogen bond."},"content":{"rendered":"<p>\n\t<a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13136\" target=\"_blank\" title=\"Halogen bonds 3: \u201cNitrogen tri-iodide\u201d\">Continuing my hunt<\/a>, here is a candidate for a strong(est?) halogen bond, this time between Se and I.[cite]10.1021\/ic50038a006[\/cite]. <a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/12\/OXSELI.jpg\"><img decoding=\"async\" alt=\"OXSELI\" class=\"aligncenter size-full wp-image-13159\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/12\/OXSELI.jpg\" width=\"250\" \/><\/a> The features of interest include:\n<\/p>\n<ol>\n<li>\n\t\tThe six-membered ring is in the chair conformation.\n\t<\/li>\n<li>\n\t\tThe (relatively enormous) I&#8230;I substituent is <strong>axial<\/strong>!\n\t<\/li>\n<li>\n\t\tIt is attached to the Se rather than the O.\n\t<\/li>\n<li>\n\t\tThe Se&#8230;I distance is 2.75&Aring;, some 1.13&Aring; shorter than the combined atom ver der Waals radii (1.90 + 1.98 = 3.88)\n\t<\/li>\n<li>\n\t\tThe Wiberg bond index is 0.42 for the Se-I bond and 0.63 for the I-I bond (at the crystal geometry). It is tending towards a symmetrical disposition of the central iodine (a feat <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13136\" target=\"_blank\" title=\"Halogen bonds 3: \u201cNitrogen tri-iodide\u201d\">also achieved<\/a> by the iodine in the NI<sub>3<\/sub> complex).\n\t<\/li>\n<li>\n\t\tThe NBO E(2) perturbation involving donation from the Se lone pair into the I-I antibond is <strong>77<\/strong> kcal\/mol, almost twice the value of the one <a href=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13105\" target=\"_blank\" title=\"Halogen bonds 2: The DABCO-Iodine structure.\">involving DABCO&#8230;I-I<\/a>&nbsp;and way above the values found for the related hydrogen bond.\n\t<\/li>\n<li>\n\t\tThe B3LYP+D3\/Def2-TZVPP+PP(I) optimised structure expands the Se-I bond distance to 3.04 and contracts the I-I distance to 2.81&Aring; indicating (as with DABCO&#8230;I-I) that there may be compression of this bond induced by the lattice.\n\t<\/li>\n<li>\n\t\tThe NCI surface shows a classical &quot;strong&quot; interaction between Se and I (blue), but significant additional features arising from the axial hydrogens that might account for the axial orientation of the Se&#8230;I-I group. <figure id=\"attachment_13169\" aria-describedby=\"caption-attachment-13169\" style=\"width: 200px\" class=\"wp-caption aligncenter\"><img decoding=\"async\" alt=\"Click for  3D\" class=\"size-full wp-image-13169\" onclick=\"jmolInitialize('..\/Jmol\/');jmolSetAppletColor('white');jmolApplet([450,450],'load wp-content\/uploads\/2014\/12\/SeI_den.cub.xyz;isosurface colour red blue wp-content\/uploads\/2014\/12\/SeI_den.cub.jvxl translucent;');\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/12\/SeI1.jpg\" width=\"200\" \/><figcaption id=\"caption-attachment-13169\" class=\"wp-caption-text\">Click for 3D<\/figcaption><\/figure>\n\t<\/li>\n<li>\n\t\tFor good measure, here is the complete crystal structure search, defining any non-bonded contact between any element of group six and group seven that is &lt;0.5&Aring; shorter than the van del Waals contact. Our candidate is on the left hand edge of the plot. <a href=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/12\/Se-I.jpg\"><img decoding=\"async\" alt=\"Se-I\" class=\"aligncenter size-full wp-image-13160\" src=\"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/12\/Se-I.jpg\" width=\"400\" \/><\/a>\n\t<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>Continuing my hunt, here is a candidate for a strong(est?) halogen bond, this time between Se and I.[cite]10.1021\/ic50038a006[\/cite]. The features of interest include: The six-membered ring is in the chair conformation. The (relatively enormous) I&#8230;I substituent is axial! It is attached to the Se rather than the O. The Se&#8230;I distance is 2.75&Aring;, some 1.13&Aring; [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,11],"tags":[408,692],"class_list":["post-13158","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","category-interesting-chemistry","tag-chair","tag-crystal-structure-search"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/13158","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=13158"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/13158\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=13158"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=13158"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=13158"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}