Bond valence parameters
Information about 'bvparmxxxx.cif' (xxxx is the year of revision of the file)
bvparmxxxx.cif files are text files that list the parameters Ro and B in the equation:
where R is the length of a bond between the two given atoms and the bond valence is a measure of the strength of the bond. The bond valence has the property that its sum around each atom in a compound is equal to the valence (oxidation state) of that atom. The bond valence is frequently used to validate newly determined crystal structures, but it has many other uses in the analysis and modelling of crystal structures.
Full details of the bond valence model can be found in I. D. Brown, The Chemical Bond in Inorganic Chemistry: The Bond Valence Model, published by Oxford University Press, 2002.
I have compiled this list from values of bond valence parameters reported in the papers cited in the file. The list is reasonably comprehensive, but I omitted some earlier parameter determinations that did not differ significantly from values that were already in the list. Where significantly different values have been reported in the literature, I have listed them in what I believe to the decreasing order of reliability. In that way a reading program can default to a bond's first occurrence in the list. In some cases, where no parameters are available in the literature I have suggested values. These carry the comment 'unchecked' and should be used with caution.
I do not warrant the accuracy of any of these numbers. The responsibility lies with the user to ensure that the values used are appropriate. Ro and B are not independent of each other, and using a different value of B necessarily requires a different value of Ro. The parameters also depend on the maximum distance that is considered to be a bond, see for example reference c in the bvparmxxxx.cif file. In most cases this distance can be taken as around 3 Å. Eqn (1) works well provided the range of bond lengths is not too large. For bonds such as O-H that are known with a wide range of distances, eqn (1) is only valid if different parameters are used for different ranges.
Bond valence parameters for bonds formed by atoms whose oxidation state is given as 9 do not have an oxidation state specified in the original paper. They may apply to a particular, but unspecified, oxidation state or they may be intended to apply to all oxidation states.
The ammonium ion is listed under the symbol NH.
All values on the right hand side of eqn (1) are in ångström units. The bond valence is given in valence units (vu) which represent the number of electron pairs that form the bond.
The list is formatted and is designed to be read either as a crystallographic information file (CIF) or, if the text is stripped out, as a fixed format file.
I. David Brown
Hamilton, Ontario, Canada
bvparm2016.cif: 2016 version, additional references (bl to bs) (posted 2016-11-03)
bvparm2013.cif: 2013 version, some references corrected (posted 2016-03-18)
bvparm2013.cif: 2013 version (posted 2013-10-16)
bvparm2011.cif: 2011 version