Transition Metal

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 least one ion is present as a complex.

The coordination compounds are named in the following way:

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.

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 to -o; -ate to -ato; -ite to -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.  

Exercise

Give the systematic names for the following coordination compounds:

1. [Cr(NH₃)₃(H₂O)₃]Cl₃

2. [Pt(NH₃)₅Cl]Br₃

3. [Pt(H₂NCH₂CH₂NH₂)₂Cl₂]Cl₂

4. [Co(H₂NCH₂CH₂NH₂)₃]₂(SO₄)₃

5. K₄[Fe(CN)₆]