{"id":11538,"date":"2013-11-05T17:40:43","date_gmt":"2013-11-05T17:40:43","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=11538"},"modified":"2013-11-05T17:40:43","modified_gmt":"2013-11-05T17:40:43","slug":"multiple-personalities-of-magnesium","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=11538","title":{"rendered":"Multiple personalities of  Magnesium."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"11538\">\n<p>The following is a short question in a problem sheet associated with introductory organic chemistry.<\/p>\n<ul>\n<li><strong>Q<\/strong>: &#8220;<em>Show curly arrows for the formation of the product of the following reaction, together with a Lewis representation of that product: Et<sub>2<\/sub>O + MgBr<sub>2<\/sub><\/em>&#8220;.<\/li>\n<li><strong>A<\/strong>:\u00a0<em>Et<sub>2<\/sub>O<sup>+<\/sup>-Mg<sup>&#8211;<\/sup>Br<sub>2<\/sub><\/em> (a product by the way that is known as magnesium bromide ethyl etherate, and which is commercially available as a solution).<\/li>\n<\/ul>\n<p>First a few tutor-like comments. The Mg is tri-coordinate in this simple representation, and if we assume that the bonds are covalent, has six electrons in the Mg valence shell. In modern notation, the Mg has a formal charge of -1 and the oxygen +1. The Mg thus does not have a filled 3s\/3p valence shell, which would be eight.\u00a0But few (students or tutors) go on to apply a reality check.\u00a0So here is one.<\/p>\n<p>The reality check involves a search for a crystal structure, which is really trivial to set up. And what we find are the following.<\/p>\n<ol>\n<li>The first hit with exactly this stoichiometry has the CCDC code\u00a0<strong>TOQKIT<\/strong> and a polymeric structure as below. Each Mg is coordinated by four (bridged) bromines and one oxygen, giving <em>trigonal bipyramidal<\/em> penta-coordination. The valence electron count at Mg is now eight, but distributed around five bonds, not four. Since we no longer have formal Lewis two-electron covalent bonds, it is difficult to assign a Lewis-like charge to the atoms.\u00a0<br \/>\n<div id=\"attachment_11541\" style=\"width: 317px\" class=\"wp-caption aligncenter\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-11541\" data-attachment-id=\"11541\" data-permalink=\"https:\/\/www.rzepa.net\/blog\/?attachment_id=11541\" data-orig-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?fit=512%2C344&amp;ssl=1\" data-orig-size=\"512,344\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;}\" data-image-title=\"TOQKIT\" data-image-description=\"\" data-image-caption=\"&lt;p&gt;Click for  3D&lt;\/p&gt;\n\" data-medium-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?fit=300%2C201&amp;ssl=1\" data-large-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?fit=450%2C302&amp;ssl=1\" class=\" wp-image-11541 \" onclick=\"jmolInitialize('..\/Jmol\/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([500,500],'load wp-content\/uploads\/2013\/11\/TOQKIT.mol;');\" alt=\"Click for  3D\" src=\"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?resize=307%2C206\" width=\"307\" height=\"206\" srcset=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?w=512&amp;ssl=1 512w, https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/TOQKIT.jpg?resize=300%2C201&amp;ssl=1 300w\" sizes=\"auto, (max-width: 307px) 100vw, 307px\" \/><p id=\"caption-attachment-11541\" class=\"wp-caption-text\">Click for 3D<\/p><\/div>\n<\/li>\n<li>The next hit actually corresponds to the stoichiometry 2R<sub>2<\/sub>O + MgBr<sub>2<\/sub> (R=thf). This again is polymeric, but differs from the first structure in having <em>octahedral<\/em> Mg (six coordination).<br \/>\n<div id=\"attachment_11544\" style=\"width: 303px\" class=\"wp-caption aligncenter\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-11544\" data-attachment-id=\"11544\" data-permalink=\"https:\/\/www.rzepa.net\/blog\/?attachment_id=11544\" data-orig-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?fit=544%2C536&amp;ssl=1\" data-orig-size=\"544,536\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;}\" data-image-title=\"MGBEET\" data-image-description=\"\" data-image-caption=\"&lt;p&gt;Click for  3D.&lt;\/p&gt;\n\" data-medium-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?fit=300%2C295&amp;ssl=1\" data-large-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?fit=450%2C443&amp;ssl=1\" class=\" wp-image-11544  \" onclick=\"jmolInitialize('..\/Jmol\/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([500,500],'load wp-content\/uploads\/2013\/11\/MGBEET.mol2;');\" alt=\"Click for  3D.\" src=\"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?resize=293%2C290\" width=\"293\" height=\"290\" srcset=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?w=544&amp;ssl=1 544w, https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/MGBEET.jpg?resize=144%2C144&amp;ssl=1 144w\" sizes=\"auto, (max-width: 293px) 100vw, 293px\" \/><p id=\"caption-attachment-11544\" class=\"wp-caption-text\">Click for 3D.<\/p><\/div>\n<\/li>\n<li>OK, even more ether: 4R<sub>2<\/sub>O + MgBr<sub>2<\/sub>. Finally, non polymeric but again with six-coordinate <em>octahedral<\/em> Mg. The Mg again has a filled valence octet, and again the bonds are not two-electron ones, hence no charges are attempted.\u00a0So just a change in the stoichiometry can result in fascinating changes to the resulting structure.<br \/>\n<div id=\"attachment_11545\" style=\"width: 317px\" class=\"wp-caption aligncenter\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-11545\" data-attachment-id=\"11545\" data-permalink=\"https:\/\/www.rzepa.net\/blog\/?attachment_id=11545\" data-orig-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?fit=568%2C560&amp;ssl=1\" data-orig-size=\"568,560\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;}\" data-image-title=\"ZZZ\" data-image-description=\"\" data-image-caption=\"&lt;p&gt;Click for  3D&lt;\/p&gt;\n\" data-medium-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?fit=300%2C295&amp;ssl=1\" data-large-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?fit=450%2C444&amp;ssl=1\" class=\" wp-image-11545  \" onclick=\"jmolInitialize('..\/Jmol\/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([500,500],'load wp-content\/uploads\/2013\/11\/ZZZVBQ.mol2;');\" alt=\"Click for  3D\" src=\"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?resize=307%2C302\" width=\"307\" height=\"302\" srcset=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?w=568&amp;ssl=1 568w, https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/ZZZ.jpg?resize=300%2C295&amp;ssl=1 300w\" sizes=\"auto, (max-width: 307px) 100vw, 307px\" \/><p id=\"caption-attachment-11545\" class=\"wp-caption-text\">Click for 3D<\/p><\/div>\n<\/li>\n<li>Finally, a variation; benzyl magnesium bromide (a Grignard reagent) shows<em> tetrahedral<\/em> coordination.<\/li>\n<\/ol>\n<div id=\"attachment_11557\" style=\"width: 312px\" class=\"wp-caption aligncenter\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-11557\" data-attachment-id=\"11557\" data-permalink=\"https:\/\/www.rzepa.net\/blog\/?attachment_id=11557\" data-orig-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?fit=560%2C432&amp;ssl=1\" data-orig-size=\"560,432\" data-comments-opened=\"1\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;}\" data-image-title=\"XECTOQ\" data-image-description=\"\" data-image-caption=\"&lt;p&gt;Click for 3D&lt;\/p&gt;\n\" data-medium-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?fit=300%2C231&amp;ssl=1\" data-large-file=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?fit=450%2C347&amp;ssl=1\" class=\" wp-image-11557  \" onclick=\"jmolInitialize('..\/Jmol\/','JmolAppletSigned.jar');jmolSetAppletColor('white');jmolApplet([500,500],'load wp-content\/uploads\/2013\/11\/XECTOQ.mol2;');\" alt=\"Click for 3D\" src=\"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?resize=302%2C233\" width=\"302\" height=\"233\" srcset=\"https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?w=560&amp;ssl=1 560w, https:\/\/i0.wp.com\/www.rzepa.net\/blog\/wp-content\/uploads\/2013\/11\/XECTOQ.jpg?resize=300%2C231&amp;ssl=1 300w\" sizes=\"auto, (max-width: 302px) 100vw, 302px\" \/><p id=\"caption-attachment-11557\" class=\"wp-caption-text\">Click for 3D<\/p><\/div>\n<p>Students (and tutors) who get as far as this are amply rewarded I hope!<\/p>\n<!-- kcite active, but no citations found -->\n<\/div> <!-- kcite-section 11538 -->","protected":false},"excerpt":{"rendered":"<p>The following is a short question in a problem sheet associated with introductory organic chemistry. Q: &#8220;Show curly arrows for the formation of the product of the following reaction, together with a Lewis representation of that product: Et2O + MgBr2&#8220;. A:\u00a0Et2O+-Mg&#8211;Br2 (a product by the way that is known as magnesium bromide ethyl etherate, and [&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,"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":[6],"tags":[1145,1151,287,1152,355],"class_list":["post-11538","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-grignard","tag-octahedral","tag-pence","tag-pentagonalbipyramid","tag-tetrahedral"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-306","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11538","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=11538"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/11538\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11538"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11538"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11538"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}