International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. C. ch. 9.6, p. 813
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The classification of metal–ligand bonds in Table 9.6.3.3 is based on the ligating contacting atom. Thus, all metal–boron distances appear in sections 2.1–2.3 of Table 9.6.3.3
, all metal–carbon distances in sections 3.1–3.22, and so on. Where intra-ligand interatomic distances (e.g. P—C distances in tertiary phosphines) are given in Table 9.6.3.3
, they are averaged over all metals and precede the individual metal–ligand interatomic distances for that ligand.
Table 9.6.3.3 is designated: (i) to appear logical, useful, and reasonably self-explanatory to chemists, crystallographers, and others who may use it; (ii) to permit a meaningful average value to be cited for each bond length. With reference to (ii), it was considered that a sample of bond lengths could be averaged meaningfully if: (a) the sample was unimodally distributed; (b) the sample standard deviation (σ) was reasonably small, ideally less than ca 0.04 Å; (c) there were no conspicuous outlying observations – those that occurred at > 4σ from the mean were automatically eliminated from the sample by STATS, other outliers were inspected carefully; (d) there were no compelling chemical reasons for further subdivision of the sample. It should be noted that Table 9.6.3.3
is not intended to be complete in covering all possible ligands. The purpose of the table is to provide information on the interatomic distances for ligands of the greatest chemical importance, notably for those that are simple and/or common.