List examples of positive and negative ligands?
Answer 1:
Well, metals are electron rich materials………
Explanation:
……and they tend to undergo oxidation, i.e.
\(M \rightarrow M^{+}+e^{-}\)
\(M \rightarrow M^{2+}+2 e^{-}\)
\(M \rightarrow M^{3+}+3 e^{-}\)
And non-metals, from the right hand side of the Periodic Table, tend to be electron-poor materials, and they tend to be good oxidants….
\(\frac{1}{2} O_{2}+2 e^{-} \rightarrow O^{2-}\)
or:
\(\frac{1}{2} F_{2}+2 e^{-} \rightarrow F^{-}\)
Anyway, in most exams you will be issued a standard table of redox potentials, which will give you the possible redox processes.
Answer 2:
Um, not sure for which class, but I can list 12 anions, I suppose… there are hardly any positive ligands. I’m sure you could list more negative ligands than I can think of off the top of my head if you just look at a book.
All of these use the donor pair electron-counting method (Method A in this diagram).
KEY:
- Ligand name (ligand prefix), formula (side note)
POSITIVE LIGANDS
- Nitrosyl (nitrosyl), \(\mathrm{NO}^{+}\) (triple-bonded, bonds to metal in a linear configuration)
- Cycloheptatrienyl (heptahaptocycloheptatrienyl), \(\eta^{7}-\mathrm{C}_{7} \mathrm{H}_{7}^{+}\) (binds via seven atoms at once)
NEGATIVE LIGANDS
- Nitrosyl (nitrosyl), \(\mathrm{NO}^{-}\) (double-bonded, bonds to metal in a bent configuration)
- Cyanide (cyano), \({ }^{-} \mathrm{CN}\)
- Chloride (chloro), \(\mathrm{Cl}^{-}\)
- Thiocyanate (thiocyanato), \(\mathrm{S}-\mathrm{C} \equiv \mathrm{N}^{-}\)
- Isothiocyanate (isothiocyanato), \(\mathrm{N}=\mathrm{C}=\mathrm{S}^{-}\)
- Superoxide (superoxo), \(\mathrm{O}_{2}^{-}\) (binds head-on)
- Peroxide (peroxo), \(\mathrm{O}_{2}^{2-}\) (binds side-on)
- Oxide (oxo), \(\mathrm{O}^{2-}\) (double-bonds usually, may bridge)
- π-allyl (trihaptoallyl), \(\eta^{3}-\mathrm{C}_{3} \mathrm{H}_{5}^{-}\) (binds via three atoms at once)
- Cyclopentadienyl (pentahaptocyclopentadienyl), \(\eta^{5}-\mathrm{C}_{5} \mathrm{H}_{5}^{-}\) (binds via five atoms at once)
- Methyl (methyl), \(-: \mathrm{CH}_{3}\)
- Hydroxide (hydroxo), \(\mathrm{HO}^{-}\)
The challenge is, can you keep track of which ones bind using how many electrons?