Acta Crystallographica Section B

Structural Science

Volume 59, Part 1 (February 2003)

research papers

Acta Cryst. (2003). B59, 51-59 [ doi:10.1107/S0108768102019353 ]

Crystal chemistry and binding of NO₂, SCN and SeCN to Co in cobalamins

G. Garau, S. Geremia, L. G. Marzilli, G. Nardin, L. Randaccio and G. Tauzher

Abstract: Results of the accurate crystal structure determination of NO₂Cbl·2LiCl (1), NO₂Cbl·NaCl (2), NCSCbl (3) and NCSeCbl (4), based on synchrotron diffraction data collected at 100 K, are described. The nitro group in (1) was found to be disordered with two orientations that differ by a rotation of 60° about the Co-NO₂ bond, whereas in (2) the nitro group has only one orientation. The first X-ray structural determination of a cobalamin with a Co-Se bond is reported. Comparison of the axial distances indicates that SeCN has a bond length of 2.384 (3) Å and that the trans influence on the Co-N bond is only slightly greater than that of SCN. The crystals of the thiocyanate cobalamin contain both the S- and N-bonded coordination isomers in a 3:2 ratio. The structural features of the Co-S bond in cobalamins are discussed. The crystal chemistry of cobalamins is discussed in terms of packing of roughly spherical molecules. The unit-cell parameters can be used to group the cobalamins' crystal structures in different arrays intermediate between distorted hexagonal close packing and primitive hexagonal arrangements. The structural features of cobalamins, and of cobaloximes that have the same axial fragment as the cobalamins, are reviewed and discussed in terms of the cis influence of the equatorial ligand.

Keywords: cobalamins; cobaloximes; crystal packing.


	Structure factor file (CIF format) (795.3 kbytes) Contains datablock NO2Cbl2LiCl

	Structure factor file (CIF format) (734.5 kbytes) Contains datablock NO2CblNaCl

	Structure factor file (CIF format) (931.5 kbytes) Contains datablock SCNCbl

	Structure factor file (CIF format) (796.0 kbytes) Contains datablock SeCNCbl

Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.