Question
Sun August 21, 2011 By:
 

pls explain the rules of naming coordination comps.

Expert Reply
Tue August 23, 2011

The coordination compounds are named in the following way. 

1. To name a coordination compound, no matter whether the complex ion is the cation or the anion, always name the cation before the anion

2. In naming the complex ion: Ligands are named first followed by the metal atom. Ligands are named in alphabetical order (if more than one type of ligand is there), then the metal atom or ion

3. 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 (i.e. can attach at more than one binding site) the prefixes bis-, tris-, tetrakis-, pentakis-, are used instead.

4. After naming the ligands, the central metal is named. 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. If the complex ion is an anion, the name of the metal ends with the suffix –ate. 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).

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

Example: 

K4[Fe(CN)6]

It is  potassium hexacyanoferrate(II)

 Solution: potassium is the cation and the complex ion is the anion. Since there are 4 K+ binding with a complex ion, the charge on the complex ion must be - 4.

Since each ligand carries –1 charge, the oxidation number of Fe must be +2.

The common name of this compound is potassium ferrocyanide.

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