{"id":18277,"date":"2017-05-06T19:23:48","date_gmt":"2017-05-06T18:23:48","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=18277"},"modified":"2017-05-06T19:23:48","modified_gmt":"2017-05-06T18:23:48","slug":"how-does-carbon-dioxide-coordinate-to-a-metal","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=18277","title":{"rendered":"How does carbon dioxide coordinate to a metal?"},"content":{"rendered":"
\n

Mention carbon dioxide (CO2<\/sub>) to most chemists and its properties as a metal ligand are not the first aspect that springs to mind. Here thought I might take a look at how it might act as such.<\/p>\n

There are up to\u00a0five binding modes with one metal that one might envisage:<\/p>\n

    \n
  1. Bonded\u00a0interaction with the metal via<\/em> just one oxygen atom,<\/li>\n
  2. Bonded\u00a0interaction via<\/em> just the central carbon atom,<\/li>\n
  3. Bonded\u00a0interaction via<\/em> the\u00a0\u03c0-face of one C=O double bond,<\/li>\n
  4. A weaker non-bonded interaction via<\/em> carbon, or<\/li>\n
  5. via<\/em> oxygen.<\/li>\n<\/ol>\n

    Search queries of the Cambridge structure database (CSD) for these five modes are illustrated below (dataDOI:\u00a010.14469\/hpc\/2524<\/a>), with the constraints being applied to how many bonds (of unspecified type) each atom carries, along with no disorder and no errors. Thus query 1<\/strong> is constrained by 1-coordination on one oxygen, and two on the carbon and other oxygen.\u00a0<\/p>\n

    \"\"<\/p>\n

      \n
    1. This query yields four hits:\u00a010.5517\/ccvcdq9<\/a>, 10.5517\/cc12nq6n<\/a>,\u00a010.5517\/cc12nq5m<\/a>,\u00a010.5517\/cc12nq4l<\/a>. The angle subtended at the central carbon of the\u00a0CO2<\/sub>\u00a0ranges from 172-176\u00b0, a very modest bending of the linear CO2<\/sub>. There are no examples where the metal is bonded to both oxygens.\"\"<\/li>\n
    2. The next category involves the metal binding just to the central carbon. Two examples are known, differentiated from O-coordination by a more acute angle at the central carbon of 121-132\u00b0.\"\"<\/li>\n
    3. The\u00a0\u03c0-coordinated type requires a slightly more complex search query, shown below. The \u03c0-complex is defined as adding one coordination to each of one oxygen and the carbon.\u00a0\n

      \"\"<\/p>\n

      This reveals 16 examples:
      \n \"\"<\/p>\n

      The sine of the angle subtended at the centroid of one C-O bond shows that for most of the examples, the metal is\u00a0close to perpendicular to this bond. The angle subtended at the central carbon ranges from 128-138, rather larger than the examples where the metal is bound just to the carbon. I have picked these two for illustration. The first (dataDOI:\u00a010.5517\/cc86r17<\/a>) contains both CO2<\/sub> and CO coordinated to the metal.\"\"This one (dataDOI: 10.1021\/ic101652e<\/a>) contains a short metal-centroid distance of 1.78\u00c5 (as also does\u00a010.5517\/ccz34kr<\/a>).\u00a0
      \n \"\"<\/p>\n

      There are two examples where\u00a0BOTH\u00a0\u03c0-CO bonds are coordinated to a metal;\u00a010.5517\/ccqlv7c<\/a>\u00a0and\u00a010.5517\/ccqlv8d<\/a>\u00a0(Ni-centroid distance 1.9\u00c5) but these are intriguing because the two\u00a0\u03c0-complexes are co-planar and not orthogonal.
      \n \"\"<\/p>\n<\/li>\n

    4. The final two cases are defined in the CSD database by having not so much bonds between metal and either C or O, as close intermolecular contacts typical of e.g.<\/em> hydrogen bonds. This one (dataDOI:\u00a010.5517\/cc12nq9r<\/a>) is to Fe, with a metal-C distance of 2.87\u00c5 which is significantly shorter than the anticipated sum of the van der Waals radii of the two atoms.\"\" The next (dataDOI:\u00a010.5517\/cc12npn2<\/a>) has a close approach of Co to O of 2.23\u00c5.\u00a0The angles subtended at the carbon range from 174-180\u00b0. There are no convincing examples of close non-bonded approaches of the metal to both oxygen atoms simultaneously.\"\"<\/li>\n<\/ol>\n

      It is striking that the searches (as defined above) reveal relatively few examples. This might simply be a result of how\u00a0the compounds are indexed in the CSD, reflected in the coordination constraints applied in the searches. Nevertheless, we see three quite different types of ligand-metal coordination in which bonds can be said to form and a more diffuse spectrum of weaker interactions to carbon dioxide. As a metal ligand, it is certainly interesting! Several deserve their wavefunctions looked at and I might report back on this aspect.<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      Mention carbon dioxide (CO2) to most chemists and its properties as a metal ligand are not the first aspect that springs to mind. Here thought I might take a look at how it might act as such. There are up to\u00a0five binding modes with one metal that one might envisage: Bonded\u00a0interaction with the metal via […]<\/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":[1754],"tags":[1412,2134,60,510,1416,2158,1587,2173,246,2179,2185,1741,733,2195],"class_list":["post-18277","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining","tag-carbon","tag-carbon-capture-storage","tag-carbon-dioxide","tag-chemical-bonding","tag-chemistry","tag-environment","tag-ligand","tag-ligand-metal-coordination","tag-metal","tag-metal-ligand","tag-propellants","tag-search-queries","tag-search-query","tag-short-metal-centroid-distance"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-4KN","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18277","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=18277"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/18277\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=18277"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=18277"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=18277"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}