1. Order of Ions
Split the complex molecule into its cation and anion. In complex, cation is named first, followed (after a space) by the name of the anion in accordance with the usual nomenclature (regardless of the nature of the complex ion) e.g.
In K4[Fe(CN)6], we name K+ first and then [Fe(CN)6]4‒
In [Cu(NH3)4]SO4, we will call [Cu(NH3)4] first and then SO42‒.
2. Naming of Ligands
In complex ion (whether cation or anion) or in neutral complex, Ligands are named before the metal ion i.e. all ligands are named first [which are listed together as one word without any separation by hyphens] followed by the name of the central atom with its oxidation state in roman numerals in parenthesis (the metal ion or atom is written before the ligands in the chemical formula of complex).
(a) Names of negative ligands end in ‘–O’.
If the name of the compound ligands ends with –ide, –ite or –ate, it is changed respectively to –ido, –ito or –ato.
[For some simple ligand, the ending –ide is changed simply to –O e.g. F– is called Fluoro, OH– is called hydroxo, oxide is called oxo, azide is called azido, amide is called amido]
(b) Neutral ligands are named as such. (Many of them have special names(.
(c) Positively charged ligands end in “ium”.
3. Order of Ligands
All ligands are listed in alphabetic order without any preference order i.e. If there are two or more ligands of the same type (say negative), these are listed in alphabetic order (disregarding the prefixes). The numerical prefixes (di, tri, bis, tris etc.) are not considered for alphabetizing purpose.
4. Multiplicity of Monodentate ligands
The number of each kind of one same type of ligands in the complex ion is specified by using the Greek prefixes di, tri, tetra, penta, hexa etc. for two, three, four, five and six etc. respectively.
5. Multiplicity of Polydentate ligands
The number of each kind of one polydentate ligands is indicated by bis for two, tris for three, tetrakis for four and so on and its name is enclosed in parenthesis. If the ligand is already having common numerical Greek prefixes like di, tri etc. in its name, use is made of bis, tris, tetrakis, pentakis etc. e.g.
6. Termination of name of metal
1. The suffix "–ate” is used in name of metal (central atom) in case of anionic complex i.e. if the complex ion is negatively charged then the name of the metal end in “ate”.
2. The name of central atom is unchanged in case of cationic complex or neutral complex.
3. Sometimes, the Latin name of the metal is used when the English name is clumsy.
For example,
7. Oxidation number of central metal ion or atom
The oxidation number of the metal ion or atom is represented by Roman numeral in parenthesis written after its name.
e.g.
Common name of normal cation (without numeral prefix) + Name of ligand (with numeral prefix) + Latin Name of central metal ion along with suffix ate + Oxidation number in parenthesis (in Roman number).
Name of ligand (with numeral prefix) + Common Name of central metal ion + Oxidation number in parenthesis (in Roman number) + Common name of normal anion (without numeral prefix).
Name of ligand (with numeral prefix) + Common Name of central metal ion + Oxidation number in parenthesis (in Roman number).
Name of ligands are written in alphabetical order.
Solution
(i) First complex splits into its cation and anion. Here potassium (K) is cation and [Fe(CN)6] is anion. Since there are 3K+, the charge on anion is 3– (the anion is complex).
| (ii) While naming a complex, the name of cation is written first followed by the name of anion. In complex anion, all ligands are named first followed by the name of central metal suffixed by ate which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis. Since ligand is negative, so its ending is O i.e. cyano prefixed by hexa indicating coordination number. |
Solution
(i) First complex splits into its cation and anion. Here chlorine (Cl) is anion and [Cr(NH3)4Cl2] is cation (which is complex). Since there are 2Cl–, the charge on cation is 2+.
| (ii) While naming a complex, the name of the cation is written first followed by the name of anion. In complex cation, all ligands are named first, followed by the name of central metal (without any change of its original name) which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis and then counter anion (Cl-). There are two types of ligands one is negative (chloro) and other is neutral (ammine) which are listed alphabetically. |
Solution
(i) This is a neutral complex having net zero charge.
(ii) While naming a neutral complex, the name of the ligands are written first followed by the name of the central atom (without any change of its original name) which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis. There are two types of ligands one is negative (nitro) and other is neutral (aquo). They are listed alphabetically.
Solution
(i) This is an anionic complex ion.
(ii) While naming complex anion, all ligands are named first followed by the name of central metal suffixed by ate which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis. Since ligand is negative, so its ending is O i.e. thiocyanato prefixed by hexa indicating coordination number. Suffix ion is added after parenthesis.
Solution
(i) This is a cationic complex ion.
(ii) While naming complex cation, all ligands are named first followed by the name of central metal (without any change of its original name) which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis. There are two types of ligands one is negative (chloro) so its ending is –O i.e. chloro prefixed by di indicating its multiplicity and other is neutral (H2O) called as aquo prefixed by di showing its multiplicity and they are listed alphabetically. Suffix ion is added after parenthesis
Solution
(i) First complex splits into its cation and anion. Here sulphate (SO42–) is anion and [Co(H2NCH2CH2NH2)3]2+ is cation (which is complex). The sulphate has a charge of –2 and is the counter anion in this molecule. Since there are 3SO42–, the charge on cation is 6+. Since it takes 3 sulfates (SO42–) to bond with two complex cations, the charge on each complex cation must be +3. Since ethylenediamine is a neutral molecule, the oxidation number of cobalt in the complex ion must be +3.
(ii) While naming a complex, the name of the cation is written first followed by the name of anion. In complex cation, all ligands are named first, followed by the name of central metal (without any change of its original name) which in turn is followed by its oxidation number indicated by Roman numerals in parenthesis. There is only one type of ligand i.e. ethylenediamine). Again, remember that you never have to indicate the number of cations and anions in the name of a complex
1. The formula of a coordination complex is written in a different order than its name.
2. The chemical symbol of the metal center is written first. The ligands are written next, with anion ligands coming before neutral ligands. If there is more than one anion or neutral ligand, they are written in alphabetical order according to the first letter in their chemical formula.
3. In a coordination compound's name, when one of the ions is just an element, the number of atoms is not indicated with a prefix. Since it still has to be written in the formula, it is determined by balancing the overall charge of the compound.
For example, tetrafluorochromium(VI) chloride becomes [CrF4]Cl2.
Solution
(i) First identify the cation and anion of complex. Here cation is complex while anion is chloride.
(ii) In this cationic complex, central atom Cr having oxidation state of +3 (III) is surrounded by 6 neutral ligands water (denoted by aquo). The formula of cationic complex should be enclosed in square bracket. The central atom is written first followed by ligands.
(iii) Since cationic complex contains 3+ charge, therefore, 3Cl atoms should be placed after coordination sphere to balance its charge. Thus the formula of the compound is:
Solution
(i) First identify the cation and anion of complex. Here cation is sodium while anion is complex.
(ii) In this anionic complex, central atom cobalt having oxidation state of +3 (III) is surrounded by 6 negative ligands cyano (CN–). The formula of anionic complex is enclosed in square bracket. The central atom is written first followed by ligands.
(iii) Since anionic complex contain 3– charge, therefore, 3Na atoms should be placed prior to coordination sphere to balance its charge. Thus the formula of the compound is:-
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