Modifier to intermediate: alkalis and alkaline earths
Cs1+
8
1.74
0.10
0.7
Rb1+
8
1.61
0.11
0.8
K1+
8
1.51
0.12
0.8
Na1+
6
1.02
0.18
0.9
Li1+
4, 6
0.59, 0.76
0.26, 0.22
1.0
Ba2+
8
1.42
0.26
0.9
Sr2+
8
1.26
0.29
1.0
Ca2+
6, 8
1.00, 1.12
0.36, 0.33
1.0
Mg2+
4, 6
0.57, 0.72
0.53, 0.46
1.2
Be2+
4
0.27
0.75
1.5
Modifier to intermediate: selected others
Sn2+
8e
1.26
0.29
1.8
Pb2+
4, 8e
0.98, 1.29
0.37, 0.28
1.9
Mn2+
6
0.83f
0.42
1.5
Fe2+
6
0.78f
0.44
1.8
Zn2+
4, 6
0.60, 0.74
0.52, 0.45
1.6
Ni2+
4, 6
0.55, 0.69
0.55, 0.48
1.9
La3+
8
1.16
0.47
1.1
Nd3+
8
1.11
0.49
1.1
Er3+
8
1.00
0.54
1.2
Y3+
8
1.02
0.53
1.2
Sc3+
6
0.75
0.67
1.3
Sb3+
4e
0.76
0.67
1.9
Zr4+
8
0.84
0.83
1.4
U4+
6
0.89
0.79
1.7
Mo6+
4, 6
0.41, 0.59
1.92, 1.58
1.8
a Common coordination numbers; others may occur. Five‐coordinate states are also known for many cations listed with 4 and 6 coordination (e.g. Al, Si, Ti, Ni), which have intermediate radii and field strengths.
b Cation field strength, valence divided by square of cation–oxygen distance, with the radius of the latter taken as 1.36 Å, the typical value for three‐coordinated O.
c Pauling electronegativity, from Pauling, L. (1970). General Chemistry. San Francisco: W.H. Freeman.
d “Network former” description is generally most appropriate for lower coordination numbers.
e Lone‐pair electronic structure may lead to lower coordination than expected from radius.
