Shannon Effective Ionic Radii

This page presents electronic versions of the table of crystallographic and effective ionic radii by R.D. Shannon. Examples of usage listed below.
Please send comments to: David Van Horn.

Link to Acta Crystallographica for Original Article

"Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides." R. D. Shannon Acta Cryst. A32, 751-767.

Copyright © International Union of Crystallography. Reproduced with permission.

Choose an electronic version of the Table

Tab Delimited Text File. (.txt - Import into your favorite software package)

Excel Spreadsheet. (.xls - It's just so dang useful.)

Notes and comments on Electronic Version

You are welcome to freely use the electronic tables.  If you utilize one of the files above and make public reference, please reference the original article and "Electronic Table of Shannon Ionic Radii, J. David Van Horn, 2001, downloaded MO/DA/YEAR."

The electronic version differs from the original in the inclusion of a record number for the first column. Also added is a column of charge/ionic radius; see Example 1 below.

Abbreviations used: HS=high spin, LS=low spin,R from r3 vs V plots, C=calculated, E=estimated, ?=doubtful, *=most reliable, M from metallic oxides.

Example 1:  How is Iron(III) like Plutonium(IV)?

In designing sequestering agents for waste cleanup or decorporation agents for accidental ingestion of actinides, researchers often turn to ‘model’ metal cations to avoid the costs and risks associated with using actinide elements.  Lanthanides are sometimes used as actinide mimics, and are well suited for the later elements in the row (compare Nd(III) to Am(III) or Cm(III)). However, the early actinides are multifaceted elements with many fine points in their chemistry. The biological activity of Pu(IV) in mimicking Fe(III) pointed to similar characteristics in these two cations, which can be highlighted by comparison of their ‘charge to radius ratio’. Compare:

Record #

ION

Ox. State

Coord. Num.

Crystal Radius

Ionic Radius

Z/Ionic Radius

77

Ce +4

4

6

1.01

0.87

4.598

280

Np +4

4

6

1.01

0.87

4.598

158

Fe +3

3

6 (H.S.)

0.785

0.645

4.651

231

Mn +3

3

6 (H.S.)

0.785

0.645

4.651

343

Pu +4

4

6

1

0.86

4.651

463

V +3

3

6

0.78

0.64

4.688

While oxidation state and ionic radius are different for Ce(IV), Fe(III), and Pu(IV), their charge to radius ratios (a rough surface charge measure) are similar. Ce(IV) is the best non-radioactive model for Pu(IV), as might be expected. While models have their use, ultimately the actinides should be studied directly.

Exercise:Another better guide might be to compare charge to surface area (A = 4 p r2); this is readily done using the spreadsheet. A) Set up an extra column on the spreadsheet, and enter the equation, Z/A (Z=charge, A=area (see above)). B) Compare charge to surface ratios of Pu(IV) to Fe(III), to Ce(IV)[coordination numbers 6 and 8, or others]. What is the result? Which cations are most alike? Different?

Example 2: Can the ionic radius of Pb(II) be linked to its toxicity?

Lead poisoning of children in major cities is a continuing problem. While lead-based paint is thought to be the major factor, urban sites with contaminated soil may be a major source of the observed human exposure. Lead is thought to coordinate to free (lone) sulfhydryl (-SH) groups on proteins in the body, thus potentially altering their function. Additionally, there is evidence that lead affects processes in the body that involve calcium. Some of the effects of lead poisoning include metabolic disorders, problems with nervous system development and functioning, and other diseases.

Can a survey of lead ion characteristics point to a partial explanation of its deleterious effects? The table below lists a number of (+2) cations, both biologically healthful and harmful.

ION

Coord. #

Ionic Radius

Z/I.R.

Pb+2

6

1.19

1.68

Pb+2

8

1.29

1.55

Pb+2

10

1.40

1.43

Ca +2

6

1.00

2.00

Ca +2

8

1.12

1.79

Ca +2

10

1.23

1.63

Zn+2

4

0.60

3.33

Zn+2

6

0.74

2.70

Zn+2

8

0.90

2.22

Mg+2

4

0.57

3.51

Mg+2

6

0.72

2.78

Mg+2

8

0.89

2.25

Cd +2

4

0.78

2.56

Cd +2

6

0.95

2.11

Cd +2

8

1.10

1.82

Cd +2

12

1.31

1.53


The first noticeable thing in this comparison is the difference in ionic radii of lead and calcium versus zinc and magnesium; the latter ions are significantly smaller. Highlighted in red are lead(II), calcium(II) and cadmium(II) with coordination number 8. The similarity suggests a role for lead in replacing calcium, potentially affecting processes associated with calcium. A comparison of charge to radius ratios (last column) also points to similarities between the metals that may be clues to their activities in biological systems.

Exercise: A) Compare charge to surface area, as in the example above. B) Is there literature comparing the physical characteristics of lead(II) to calcium(II)? (Internet, Literature database, Library) C) Investigate how lead poisoning is treated. Do chelating agents target ion size, charge, ligand affinities, or other features of heavy metals?
 

Page and Spreadsheet created by
David Van Horn.
Last updated 1/31/07