When do you use parentheses when naming transition metal complexes?

Feb 12, 2016

There's no hard and fast rule; generally, for more complex ligands, like polydentates (chelating ligands), you would.

When there is more than one complex ligand (not tooth, but ligand), you put bis, tris, tetrakis, pentakis, etc. because it looks better than something like di(diethylenediamine) or di(dialkyldithiocarbamato). Use your best judgment.

Some examples and their formula abbreviations are:

• ethylenediamine (en) ~ bidentate (contributes $0$)

where the first ligand is a trans isomer, the second is a $\Lambda$ isomer, and the third is a $\Delta$ isomer. (Rotate the second isomer clockwise ${90}^{\circ}$ and the third isomer counterclockwise ${90}^{\circ}$ to get the standard orientation.)

In this case, since there are two ethylenediamines, but the ligand already has "di" in it (and is complex), we put "bis" because it sounds good.

• 1,10-phenanthroline (o-phen / phen) ~ bidentate (contributes $0$)

where the first structure is a trans isomer, the second is a $\Delta$ isomer, and the third is a $\Lambda$ isomer. (Flip the second two isomers upside-down to get the standard orientation.)

In this case, the name is just complex, and the ligand is bidentate, so we write "bis(o-phenanthroline)" in the name but ${\text{(o-phen)}}_{2}$ in the formula.

• dialkyldithiocarbamato (dtc) ~ bidentate (contributes $- 1$)

where the first structure is a trans isomer, the second is a $\Delta$ isomer, and the third is a $\Lambda$ isomer. (Flip the second two isomers upside-down to get the standard orientation.)

The ${\text{OH}}^{-}$ contributes a $\left(-\right)$ charge, and the $\text{dtc}$ contributes a total of $- 1 \times 2 = - 2$ charge, making the whole structure neutral. Obviously with two "di"s in the name, we should use "bis" instead of "di" to indicate two of them.

• oxalato (ox) ~ bidentate (binds via oxygens in an acetate resonance structure; contributes $- 2$)

where the first structure is a trans isomer, the second is a $\Delta$ isomer, and the third is a $\Lambda$ isomer. (Flip the second two isomers upside-down to get the standard orientation.)

Each oxalato ligand contributes $- 1$ per oxygen for a total of $- 4$, and the chlorine and fluorine contribute $- 1$ each, making the structure a $3 -$ charge. Since the charge is negative, we use "chromate(III)" instead of "chromium(III)".