Abstract
Bond-length distributions are examined for three configurations of the H+ ion, 16 configurations of the group 14–16 non-metal ions and seven configurations of the group 17 ions bonded to oxygen, for 223 coordination polyhedra and 452 bond distances for the H+ ion, 5957 coordination polyhedra and 22 784 bond distances for the group 14–16 non-metal ions, and 248 coordination polyhedra and 1394 bond distances for the group 17 non-metal ions. H...O and O—H + H...O distances correlate with O...O distance (R 2 = 0.94 and 0.96): H...O = 1.273 × O...O – 1.717 Å; O—H + H...O = 1.068 × O...O – 0.170 Å. These equations may be used to locate the hydrogen atom more accurately in a structure refined by X-ray diffraction. For non-metal elements that occur with lone-pair electrons, the most observed state between the n versus n+2 oxidation state is that of highest oxidation state for period 3 cations, and lowest oxidation state for period 4 and 5 cations when bonded to O2−. Observed O—X—O bond angles indicate that the period 3 non-metal ions P3+, S4+, Cl3+ and Cl5+ are lone-pair seteroactive when bonded to O2−, even though they do not form secondary bonds. There is no strong correlation between the degree of lone-pair stereoactivity and coordination number when including secondary bonds. There is no correlation between lone-pair stereoactivity and bond-valence sum at the central cation. In synthetic compounds, PO4 polymerizes via one or two bridging oxygen atoms, but not by three. Partitioning our PO4 dataset shows that multi-modality in the distribution of bond lengths is caused by the different bond-valence constraints that arise for Obr = 0, 1 and 2. For strongly bonded cations, i.e. oxyanions, the most probable cause of mean bond length variation is the effect of structure type, i.e. stress induced by the inability of a structure to follow its a priori bond lengths. For ions with stereoactive lone-pair electrons, the most probable cause of variation is bond-length distortion.
Highlights
A large number of inorganic crystal structures have been refined to relatively high degrees of accuracy and precision in the past few decades
We have examined the distribution of bond lengths for 135 ions bonded to oxygen in 462 configurations using 180 331 bond lengths extracted from 9367 refined crystal structures (Gagne & Hawthorne, 2016, 2018; Gagne, 2018); these data involve most ions of the periodic table and all coordination numbers in which they occur
The metalloid and poor-metal ions are treated with their respective families in our series on bondlength distributions for ions bonded to O2À (Gagne & Hawthorne, 2018), it is appropriate to briefly review the data for all ions here. In their analysis of lone-pair stereoactive ions, Galy et al (1975) give examples for which the lone-pair electrons are ‘fully stereoactive’, but state that in the majority of cases, they are observed in an ‘intermediate state’ between stereoactivity and inertness. This is what we observe in our data; there is a minority of cases for which longer interatomic distances to the anions are 2–3Â that of the mean bond length for the short bonds, leading to coordination numbers [2] to [4] and where the lone-pair electrons are arguably ‘fully stereoactive’
Summary
A large number of inorganic crystal structures have been refined to relatively high degrees of accuracy and precision in the past few decades. A comprehensive examination of the variation in interatomic distances of ions has yet to be done for inorganic crystal structures, despite the pivotal influence that these kinds of studies have played in organic and organometallic chemistry (e.g. Allen et al, 1987; Mayer, 1988; Orpen et al, 1989) In the first paper of this series (Gagne & Hawthorne, 2016), we reported bond-length distributions for the alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) and alkaline earth metal ions (Be2+, Mg2+, Ca2+, Sr2+ and Ba2+) in all observed coordination numbers where bonded to O2À, and gave a detailed introduction and rationale for this work and a description of the data-collection and data-filtering methods
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