Coordination Compounds
3.0 Nomenclature of Co-ordination Compounds
3.0 Nomenclature of Co-ordination Compounds
Nomenclature is very important in coordinate chemistry because of the need to have an unambiguous method of describing formulas and writting systematic names, particularly when dealing with isomers. The formulas and names adopted for coordination entities are based on the recommendations of the Internationals Union of Prime and Applied Chemistry (IUPAC).
Rules for writing IUPAC Nomenclature:
- The Positive part of a coordinate compound is named first and is followed by negative part.
Name of Negative Ligand:
| S. No. | Ligand | Name |
| 1 | $C{l^ - }$ | chlorido,chloro |
| 2 | ${F^ - }$ | flouro,flourido |
| 3 | $O_2^{2 - }$ | peroxido (or) peroxo |
| 4 | ${O^{2 - }}$ | oxido (or) oxo |
| 5 | $SO_4^{2 - }$ | sulphato |
Note: Organic anions when donor atom is carbon then no need of adding "o"
- The name of neutral ligand has to be written as such
en = ethyl diamine, dien = diethylene triamine
Note: Some of the neutral ligand have some special names such as
| S. No. | Ligand | Name |
| 1. | ${H_2}O$ | Aqua |
| 2. | $CO$ | Carbonyl |
| 3. | $NO$ | nitrosyl |
| 4. | $N{H_3}$ | ammine |
- The names of positive ligand ends with letter "ium".
Example:
| S. No | Ligand | Name |
| 1 | $N{O^ + }$ | Nitrolium |
| 2 | ${H_2}N - N{H^ + }$ | hydrazinium |
- If the complex compound consist more than one same type of ligand then we have to consider "di, tri, tetra, penta, and hexa"
- If the name of the ligand already consist the prefix like di, tri etc. then we have to use the prefix like "Bis for $2$, "Tris for $3$", "Tetrakis for $4$"
Example:
| S. No | Ligand | Name |
| 1. | ${(N{H_3})_2}$ | diamine |
| 2. | ${({(C{H_3})_2}N{H_2})_2}$ | Bis dimethyl diamine |
| 3. | ${(en)_2}$ | Tri ethylenediamine |
| 4. | ${((C{H_3})N{H_2})_2}$ | Bis methylamine |
- If the coordination compound consists of more than one ligand then they have to be written in "Alphabetical Order".
Example: Among $N{H_3}$ and $C{l^ - }$, $N{H_3}$ should be written first.
- If the complex ion is a cation, they named same as the element. For example, $Co$ in a complex cation is called cobalt and $Pt$ is called platinum. If the complex ion is an anion, the name of metal ends with the suffix "-ate". Example: ${\left[ {Co{{(SCN)}_4}} \right]^{2 - }}$ , Co in a complex is written as cobaltate and another ferrate for Fe.
- The oxidation state of a center metal atom is shown by Roman Letter numeral in bracket immediately following its name. Example: Titanium(IV)
- If a complex contains two are more metal atom, it is termed Polynuclear. the Bridging ligands which link into two metals together indicated by the prefix "$\mu $". if there are two or more bridging group of the same kind, this is indicated by di-$\mu $,tri-$\mu $ etc. The bridging group is listed alphabetically with the other group unless the symmetry of the molecule allows a similar name. If a bridging group bridge more than two metal atoms it is shown as ${\mu _3},{\mu _4},{\mu _5},{\mu _6}$ to indicate how many atoms it is bounded to.
Example: tetra ammine cobalt (III) $\mu $- amido $\mu $-nitro cobalt(III) tetra ammine nitrate
Oxidation number of cobalt is
$\begin{equation} \begin{aligned} 2x - 1 - 1 = 4 \\ x = 3 \\\end{aligned} \end{equation} $
- Sometimes a ligand may be attached through different atoms. Thus $M$-$NO$ is called nitro and $M-ONO$ is called nitrito.
Similarly, $SCN$ group may bond $M$-$SCN$ thiocyanate or $M$-$NCS$ isothiocyanate. These may be named symmetrically thiocyanate-S or thiocyanate-N to indicate which atom is bonded to be the metal. This may be extended to other cases where the mode of linkage is ambiguous.
Example:
| S.No. | Ligand | Name |
| 1. | $ \leftarrow CN$ | cyano |
| 2. | $ \leftarrow N{C^ - }$ | isocyano (or) N-cyano |
| 3. | $ \leftarrow SCN{}^ - $ | Thiocyano |
| 4. | $ \leftarrow NC{S^ - }$ | Isothiocyano (or) N-thiocyano |
Example:
1. $\left[ {Cr{{(N{H_3})}_3}{{({H_2}O)}_3}} \right]C{l_3}$ is named as:
Answer: triamminetriaquachromium(III)chloride
Explanation: The complex ion is inside the square bracket, which is a cation ($Cr$). The amine ligands are named before the aqua ligands according to alphabetic order. Since there chloride in compound, 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 molecule. Therefore, the oxidation number of chromium must be the same as the charge of the complex of the charge ion $+3$.
2. ${\left[ {Co{{({H_2}NC{H_2}C{H_2}N{H_2})}_3}} \right]_2}{(S{O_4})_3}$ is named as:
Answer: tris(ethane-1,2-diammine)cobalt(III)sulphate
Explanation: The sulphate is the counter anion in this molecule, since it take $3$ sulphates to the bond with two complex cations, the charge on the complex cation must be $+3$. Further ethane -1,2-diammine is neutral molecule. So the oxidation number of the cobalt in the complex ion must be $+3$. Remember that you can never have to indicate the number of cations and anions in the name of an ionic compound.
3. $\left[ {CoCl(N{O_2}(N{H_{3{)_4}}}} \right]N{O_3}$ is named as:
Answer: triamminechloronitrocobalt(III)nitrate (complex is anion so, we use -ate)
4. $\left[ {PtC{l_2}({C_5}{H_5}N)(N{H_3})} \right]$
Answer: amminedicloro(pyridine)platinum(II) (Complex is cation)
5. ${\left[ {CoCl{{(N{H_3})}_4}} \right]^ + }$
Answer: tetraammineedichlorocobalt(III) ion (complex is cation)
6. ${\left[ {CoCl(ONO){{(en)}_2}} \right]^ + }$
Answer: chlorobis(ethylenediamine)nitritocobalt(III) ion
7. $\left[ {{{\{ {{({C_6}{H_5})}_3}P\} }_3}Rh} \right]Cl$
Answer: tris(triphenylphosphine)rhodium(I)chloride
8. ${K_3}\left[ {Ir{{({C_2}{O_4})}_2}} \right]$
Answer: potassiumbis(oxalato)iridate(I)
9. $\left[ {Pt{{(N{H_3})}_4}C{l_2}} \right]\left[ {PtCl{}_4} \right]$
Answer: We have to write it in the form of ${\left[ {Pt{{(N{H_3})}_4}C{l_2}} \right]^{2 + }}{\left[ {PtCl{}_4} \right]^{2 - }}$. Here $Pt$ valency is $4$ and in second complex valency of $Pt$ is $2$. We can write it as Tetra ammine dichloro platinum (IV) tetrachloro platiate (II). ate is written because of second complex is anion.
