Single-bond conversion between valence and distance for oxides and fluorides, from the 2020 accumulated parameter table.
| CN | s = V/CN | R (Å) | Δ vs. current R |
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Parameters. Every value here is taken verbatim from a single source: the accumulated table of bond valence parameters compiled by I. D. Brown, bvparm2020.cif (dated 2020-11-25), distributed by the IUCr. Nothing is merged in from any other edition of that table or from any other compilation. It contributes 718 parameter sets — 488 for O2− and 230 for F− — over 91 cations and 367 cation–anion–valence combinations, drawn from 59 references. Where a combination has several published sets they appear in the compiler’s own order of decreasing reliability, and the first is selected by default.
Reading the numbers. A bond valence is dimensionless but is conventionally quoted in valence units (v.u.). The relation is an empirical fit, not a physical law: it is calibrated on bonds near their equilibrium length, and extrapolation to very short or very long contacts (roughly s < 0.04 or s > 2) is unsupported by the underlying data. B is not uniformly 0.37 Å in this edition — 291 of the 718 sets use a fitted B, including 88 of the 367 default selections, largely from the Gagné & Hawthorne (2015) refinement, which contributes 135 sets and is the single largest source in the O/F part of the table. R0 and B are strongly correlated, so never pair R0 from one reference with B from another.
Scope. This computes a single bond only. It does not sum over a coordination sphere, apply a distortion or lone-pair correction, or account for the second-neighbour terms used in the Adams (2001) parameterisation, whose sets are marked here with their own cut-off.