SME
Inorganic Chemistry
Coordination chemistry
Use this for “Find the oxidation state of iron, its d count and the coordination number in K₃[Fe(CN)₆].”
Diagram
Co with 5 NH₃ and 1 Cl: coordination number 6, octahedral.
This is an example. Type your own values to start a new problem.
ox
+
(
L
)
=
q
q is the charge on the whole bracketed complex ion and L the sum of its ligands’ charges; ox is what is left for the metal.
G
Group of the metal
example
d
d electrons
calculated
CN
Coordination number
example
Formulas
ox
=
q
−
L
+3 = 2 − (−1)
d
=
G
−
ox
6 = 9 − 3
Assumptions
•
Neutral ligands (NH₃, H₂O, CO, en) bring 0; Cl⁻, CN⁻ and OH⁻ bring −1 each; the ligand charge is their sum.
•
The d count is the metal’s group number less its oxidation state: a metal ion keeps no s electrons.
•
The coordination number counts the donor atoms bound to the metal (en gives two).
•
The picture starts from [Co(NH₃)₅Cl]²⁺ and draws as many donor atoms as the coordination number: the Cl⁻ stays, NH₃ fills the rest.
Step-by-step
WE KNOW
q = +2, L = −1, G = 9, CN = 6
FIND
oxidation state of the metal (ox), d electrons (d)
Step 1 · Find oxidation state of the metal (ox)
Use ox = q − L
The ion’s charge is the metal’s charge plus the ligands’, so take the ligands’ away.
ox = 2 − (−1)
ox = +3
Step 2 · Find d electrons (d)
Use d = G − ox
The group number counts the metal’s valence electrons; each unit of charge removes one.
d
=
9
−
3
d
=
6
→
d
6
:
6
electrons
in
the
d
orbitals.
Check
Put the numbers back in. Both sides should match.
+3 = 2 − (−1) ✓
6 = 9 − 3 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.