LIST OF PARTICIPANTS
The recently reported  crystal structure of hexacoordinate carbon now firmly identifies a species first speculated about in 1973.. I here propose an iso-electronic species which leads directly to an analogous pentacoordinated nitrogen. The logic can be expressed as follows.
- The challenge then to the synthetic community is to see if the pentacoordinate nitrogen species can be made and characterised.
- A second challenge would be whether penta-coordinated oxygen could be achieved.
Here I report some simple searches of CSD (Cambridge structure database).
- A simple search specifying merely that a single carbon have at least five other bonded (coordinated) atoms leads to 5910 hits.
- Specifying that no C-B (any bond type) must exist in the structure reduces this to 3931.
- Specifying that at least five C-C bonds to the central C must exist (any bond type) gives 8 hits, of which five do appear to be errors (the other three relate to the crystal structure discussed above).
- Specifying that at least five C-C or C-H bonds of any type must exist gives 36 hits, of which most are again probably errors. One genuine example is the recent structure of the norbornyl cation.
- Specifying that at least five N-C or N-H bonds of any type to a central N atom results in zero hits.
- Specifying that at least five O-C or O-H bonds of any type to a central O atom results in one hit, the coordination being a clear error due to disorder.
To a certain extent at least these results indicate how difficult it can sometimes be to index a structure in the CSD for the bonds it carries. I suspect the indexing is sometimes done by a human based on their own interpretations, with guidelines of course.
- M. Malischewski, and K. Seppelt, Angewandte Chemie International Edition, 2016, 56, 368-370, DOI:10.1002/anie.201608795 . The crystal structure can be viewed at DOI:10.5517/CCDC.CSD.CC1M71QM
- H. Hogeveen and P. W. Kwant, Tet. Lett., 1973, 1665. DOI:10.1016/S0040-4039(01)96023-X
- H. S. Rzepa, 2017, DOI:10.14469/hpc/2348
- H. S. Rzepa, 2017, DOI:10.14469/hpc/2747
- H. S. Rzepa, 2017, DOI:10.14469/hpc/2872
- H. S. Rzepa, 2017, DOI:cbpt
- H. S. Rzepa, 2017, DOI:cbpx
- H. S. Rzepa, 2017, DOI:10.14469/hpc/2746 and DOI:cbpx
- DOI:10.1126/science.1238849 .