Hello,
I need to estimate the bond distances of atoms in metal complexes by using the covalent and/or van-der-Waals radii.
Currently my wild guess after some thoughts is to weigh the sum of the van-der-Waals radii with the mean relation of the covalent radii to the van-der-Waals radii:
d = (rvdw1 + rvdw2) * (rcov1/rvdw1 + rcov2/rvdw2) * 0.5
This way the covalent bond distance for the same atoms are achieved. For different atoms the bond distance is somewhere between the covalent and van-der-Waals bond distance. This seemed to be a good guess, as I heard that the bond distances from the metal centre to a ligand is relatively large.
Is there any other proper way to estimate the bond distance?
Thanks and best regards,
Leonhard Niemann
In a coordination compound there many factors affecting the M-L bond. These are: the oxidation state of the metal, electronic configuration of the metal, the type of ligands, monoatomic or polyatomic, the mode of bonding of the ligand, coordination number of the complex and etc. Therefore, I am not sure that you can use a specific formula to estimate the metal ligand bond length. However، the reference suggested by Al-Noor seems to be useful and might give you interesting information.
Hi
Following up on the previous answers, I would like to stress that bond distances and atomic radii are not intrinsic properties of atoms, and hence they will change depending on each case. However, having an appreciation of bond orders by simply analysing the bond distances is a useful tool in a lot of research areas, so there have been attempts to generate lists of atomic radii that allow to get an estimation of bond distances between elements. However, there are several lists that are currently used by the research community (Pauling, Pyykkö and Alvarez are arguably some of the most popular). The bond distances are then simply calculated as the sum of the two covalent radii.
Van der Waals radii are not really meant to be used to estimate bond distances and they usually provide distances much larger than the real bonds. Therefore, I would avoid using these. In summary, there is no need to make complicated approximations to estimate the bond distances. Simply use the sum of covalent radii. If you use the three papers I mentioned earlier, you will get a range of distances which will probably provide an acceptable approximation to the real bond lengths. Here you have the references. Hope this helps.
Pauling, L. J. Am. Chem. Soc. 1947, 69, 542–553. https://pubs.acs.org/doi/abs/10.1021/ja01195a024
Pyykkö, P.; Atsumi, M. Chem. Eur. J. 2009, 15, 186–197. https://chemistry-europe.onlinelibrary.wiley.com/doi/full/10.1002/chem.200800987
Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.; Echeverría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Dalton Trans. 2008, 2832–2838. https://pubs.rsc.org/en/content/articlelanding/2008/DT/b801115j#!divAbstract
Kind regards,
Martí
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