Question

what's the easiest way to give names to coordination compounds
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Answer 1

Naming Coordination Compounds

A complex is a substance in which a metal atom or ion is associated with a group of neutral molecules or anions called ligands.Coordination compounds are neutral substances (i.e. uncharged) in which at leastone ion is present as a complex. You will learn more about coordination compounds in the lab lectures of experiment 4 in this course.

The coordination compounds are named in the following way. (At the end of this tutorial we have some examples to show you how coordination compounds are named.)

A. To name a coordination compound, no matter whether the complex ion is the cation or the anion, always name the cation before the anion. (This is just like naming an ionic compound.)

B. In naming the complex ion:

1. Name the ligands first, in alphabetical order, then the metal atom or ion. Note: The metal atom or ion is written before the ligands in the chemical formula.

2. The names of some common ligands are listed in Table 1.

� For anionic ligands end in "-o"; for anions that end in "-ide"(e.g. chloride), "-ate" (e.g. sulfate, nitrate), and "-ite" (e.g. nirite), change the endings as follows: -ide  -o; -ate  -ato; -ite  -ito

� For neutral ligands, the common name of the molecule is used e.g. H2NCH2CH2NH2 (ethylenediamine). Important exceptions: water is called ‘aqua’, ammonia is called ‘ammine’, carbon monoxide is called ‘carbonyl’, and the N2 and O2 are called ‘dinitrogen’ and ‘dioxygen’.

Table 1. Names of Some Common Ligands

Anionic Ligands

Names

 

Neutral Ligands

Names

Br-

bromo


NH3

ammine

F-

fluoro

 

H2O

aqua

O2-
oxo
NO
Nitrosyl
OH-
Hydroxo
CO
Carbonyl
CN-
cyano
O2
dioxygen
C2O42-
oxalato
N2
dinitrogen
CO32-
carbonato
C5H5N
pyridine
CH3COO-
acetato

H2NCH2CH2NH2

ethylenediamine

3. Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-. If the ligand already contains a Greek prefix (e.g. ethylenediamine) or if it is polydentate ligands (ie. can attach at more than one binding site) the prefixes bis-, tris-, tetrakis-, pentakis-, are used instead. (See examples 3 and 4.) The numerical prefixes are listed in Table 2.

Table 2. Numerical Prefixes

Number

Prefix

Number

Prefix

Number

Prefix

1

mono

5

penta (pentakis)

9

nona (ennea)

2

di (bis)

6

hexa (hexakis)

10

deca

3

tri (tris)

7

hepta

11

undeca

4

tetra (tetrakis)

8

octa

12

dodeca

 

4. After naming the ligands, name the central metal. If the complex ion is a cation, the metal is named same as the element. For example, Co in a complex cation is call cobalt and Pt is called platinum. (See examples 1-4). If the complex ion is an anion, the name of the metal ends with the suffix –ate. (See examples 5 and 6.). For example, Co in a complex anion is called cobaltate and Pt is called platinate. For some metals, the Latin names are used in the complex anions e.g. Fe is called ferrate (not ironate).

Table 3: Name of Metals in Anionic Complexes

Name of Metal

Name in an Anionic Complex

Iron

Ferrate

Copper

Cuprate

Lead

Plumbate

Silver

Argenate

Gold

Aurate

Tin

Stannate

 

5. Following the name of the metal, the oxidation state of the metal in the complex is given as a Roman numeral in parentheses.

C. To name a neutral complex molecule, follow the rules of naming a complex cation. Remember: Name the (possibly complex) cation BEFORE the (possibly complex) anion.See examples 7 and 8.

For historic reasons, some coordination compounds are called by their common names. For example, Fe(CN)63- and Fe(CN)64- are named ferricyanide and ferrocyanide respectively, and Fe(CO)5 is called iron carbonyl.

Examples Give the systematic names for the following coordination compounds:

1. [Cr(NH3)3(H2O)3]Cl3

Answer: triamminetriaquachromium(III) chloride

Solution: The complex ion is inside the parentheses, which is a cation.

The ammine ligands are named before the aqua ligands according to alphabetical order.

Since there are three chlorides binding with the complex ion, the charge on the complex ion must be +3 ( since the compound is electrically neutral).

From the charge on the complex ion and the charge on the ligands, we can calculate the oxidation number of the metal. In this example, all the ligands are neutral molecules. Therefore, the oxidation number of chromium must be same as the charge of the complex ion, +3.

2. [Pt(NH3)5Cl]Br3

Answer: pentaamminechloroplatinum(IV) bromide

Solution: The complex ion is a cation, the counter anion is the 3 bromides.

The charge of the complex ion must be +3 since it bonds with 3 bromides.

The NH3 are neutral molecules while the chloride carries - 1 charge. Therefore, the oxidation number of platinum must be +4.

3. [Pt(H2NCH2CH2NH2)2Cl2]Cl2

Answer: dichlorobis(ethylenediamine)platinum(IV) chloride

Solution: ethylenediamine is a bidentate ligand, the bis- prefix is used instead of di-