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Nomenclature - Lesson Summary

The names and formulae of coordination compounds are written by using the rules given by the IUPAC.

Rules framed by IUPAC for writing the formula of a complex:

(i) The formula of the cation, whether it is simple (or) complex is written first followed by that of the anion.


(ii) Within the coordination sphere the symbol for the central atom is written first, followed by the symbols (or) formulae for the ligands in alphabetical order, irrespective of the charge on them.

(iii) Within a coordination sphere the metal atom as well as the ligands are listed without any space between them.


(iv) The formulae for polyatomic ligands and the abbreviations used for the ligands are enclosed in brackets.


(v) If the formula for a cationic or anionic coordination sphere is to be written without that of the counter ion, then the charge, with the number before the sign, is written as a right superscript outside square brackets.

(vi) The formula for the entire coordination sphere is enclosed in square brackets.

Rules for naming coordination compounds are:

(i) In ionic coordination compounds the cation is named first and separated by a space from the anion.


(ii) While naming coordination sphere, the ligands are named first followed by the name of the central metal atom (or) the ion with its oxidation state in roman numerals in parenthesis.

(iii) If several ligands of the same type are attached to the central metal atom, then their number is indicated by using prefixes like di, tri, tetra, penta, etc. However, when the name of the ligand already includes a numerical prefix, then prefixes such as bis, tris, tetrakis and pentakis are used.


(iv) If the coordination entity is either neutral (or) cationic then usual name of the metal is used. But, when the coordination entity is an anion then name of the metal ends with the suffix 'ate'.



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