22.4: Naming Coordination Compounds

Naming Coordination Compounds:

Ligands That Are Part of a Complex: (never (rarely?) positively charged)

Ligands With No Charge:
H₂O = aqua
NH₃ = ammine
CO = carbonyl
en = ethylenediamine

Ligands With a Charge of –1:
CN^– = cyano
F^– = fluoro
Br^– = bromo
Cl^– = chloro
I^– = iodo
OH^– = hyrdoxo


Ligands With a Charge of –2:
O^2– = oxo
C₂O₄^2– = oxalato (only other bidentate ligand)
SO₄^2– = sulfato

With the exceptions of en and oxalato, all of these ligands are monodentate (one “bite”).

Rules For Naming:

1. The name of the cation comes first, the anion comes second. The name of the complex consists of two parts written together as one word. Ligands are named first and the metal atom is second.

2. Name and number the ligands in alphabetical order.
Prefixes for Numbering:
1 = mono
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona/ennea
10 = deca

3. Metal name stays intact if it is a cation. Add -ate to the end otherwise.

Name/Anion Name:
Copper/Cuprate
Gold/Aurate
Iron/Ferrate
Lead/Plumbate
Silver/Argentate
Tin/Stannate

4. Add “ion” if it is one.

Example:

What is the name of the following complex ion?

[Co(NH₃)₆]³⁺

First, name and number the ligands in alphabetical order. There is only one ligand, the NH₃, so no need to worry about alphabetizing here. This ligand is called ammine.

There are six of them, so it is hexaammine.

We know that the NH₃ molecule has no charge, and we see that the ion has a +3 overall charge, which means this must come from the cobalt, so we know the name of the metal is Cobalt(III). And since it is the cation, we can use this name instead of changing it.

The name of our complex ion then is hexaamminecobalt(III) ion.

What is the Coordination Number of this ion?

NH₃ is monodentate, and there are six of them. So C.N. = 6


Example:

[Fe(H₂O)₂(CN)₄]^2–

Name and number the ligands in alphabetical order:

(H₂O)₂ = diaqua
(CN)₄ = tetracyano

Name the metal:

H2O has no charge. CN has a –1 charge, and there are 4 of them. And the total charge on the complex ion is –2. So we have:

Charge on Fe + 0 + (–4) = –2
Charge on Fe = +2

So we know we have Iron(II). And since the complex ion is an anion, it's called ferrate(II).

The name of the complex ion is diaquatetracyanoferrate(II) ion.

All six ligands are monodentate, so C.N. = 6.


Example:

Na₃[Ti(O)₂(OH)F₂(SO₄)]

The name of the cation, Sodium, comes first.

Name and number the ligands in alphabetical order:

F₂ = difluoro
OH = hydroxo (the mono is unnecessary)
O₂ = dioxo
SO₄ = sulfato

Name the metal:

O has a charge of –2 and there are two of them. OH has a charge of –1. F has a charge of –1 and there are two of them. SO4 has a charge of –2. And since Na has a charge of +1, and it takes 3 of them to neutralize the anion, we know the charge on the anion must be –3. So:

Charge on Ti + (–2 x 2) + (–1) + (–1 x 2) + (–2) = –3
Charge on Ti = +6

So it is Titanium(VI). Since it is part of the anion, it is called titinate(VI).

The name of the complex ion is Sodium difluorohydroxodioxosulfatotitinate(VI).

It has six monodentate ligands, so the C.N. = 6.


Example:

[Os(C₂O₄)₂Cl₂]Cl₂

Notice that Cl₂ appears twice. The first time it is part of the complex. The second time, it is the anion. And just like with other ionic compounds, the Cl₂ denotes two Cl^– and not Cl₂ gas. And as the anion, chloride will be named after the complex ion.

Name and number the ligands in alphabetical order:

Cl₂ = dichloro
(C₂O₄)₂ = dioxalato

Name the metal:

C2O4 has a charge of –2 and there are two of them. Cl has a charge of –1 and there are two of them. And we know that it takes two of the Cl^– anion to neutralize the charge on the complex ion, which must be +2. So:

Charge on Osmium + (–2 x 2) + (–1 x 2) = +2
Charge on Osmium = +8

So it is Osmium(VIII). As part of the cation, it gets to keep this name.

So the name of the complex is dichlorodioxalatoosmium(VIII) chloride.


Example:

[Cd(en)₃][PtCl₆]

Here we have a complex ion as both the anion and the cation.

Special case with en:

When the name of the ligand also has a number prefix, as in ethylenediamine, there is a new set of prefixes that needs to be used to name it:
2 en = bis-
3 en = tris-
4 en = tetrakis-

Remember that Cadmium has only one oxidation state, and can only have a charge of +2, and en has no charge. So the charge on the cation is +2, which means the charge on the anion is –2. Cl has a charge of –1 and there are six of them. So:

Charge on Platinum + (–1 x 6) = –2
Charge on Platinum = +4

So, following the rules, the name of our complex compound is trisethylenediaminecadmium(II) hexachloroplatinate(IV).

Now try to write the notation for the complex ion from the name:

Example:

dicarbonyltrioxalatoaurate(IV) ion

When writing it this way, the metal comes first. Aurate(IV) = Au

dicarbonyl = (CO)₂
trioxalato = (C₂O₄)₃

charge on Au(IV) = +4
charge on (CO)₂ = 0 (neutral molecule)
charge on (C2O4)3 = –6
charge on ion = –2

[Au(CO)₂(C₂O₄)₃]^2–