Question

List examples of positive and negative ligands?

Answer 1

Well, metals are electron rich materials.........

Explanation:

......and they tend to undergo oxidation, i.e.

`MrarrM^(+) + e^-`

`MrarrM^(2+) + 2e^-`

`MrarrM^(3+) + 3e^-`

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....

`1/2O_2 + 2e^(-) rarr O^(2-)`

or......

`1/2F_2+2e^(-) rarrF^-`

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), `"NO"^(+)` (triple-bonded, bonds to metal in a linear configuration)
• Cycloheptatrienyl (heptahaptocycloheptatrienyl), `eta^7-"C"_7"H"_7^(+)` (binds via seven atoms at once)

NEGATIVE LIGANDS

• Nitrosyl (nitrosyl), `"NO"^(-)` (double-bonded, bonds to metal in a bent configuration)
• Cyanide (cyano), `""^(-)"CN"`
• Chloride (chloro), `"Cl"^(-)`
• Thiocyanate (thiocyanato), `"S"-"C"-="N"^(-)`
• Isothiocyanate (isothiocyanato), `"N"="C"="S"^(-)`
• Superoxide (superoxo), `"O"_2^(-)` (binds head-on)
• Peroxide (peroxo), `"O"_2^(2-)` (binds side-on)
• Oxide (oxo), `"O"^(2-)` (double-bonds usually, may bridge)
• `pi`-allyl (trihaptoallyl), `eta^3-"C"_3"H"_5^(-)` (binds via three atoms at once)
• Cyclopentadienyl (pentahaptocyclopentadienyl), `eta^5-"C"_5"H"_5^(-)` (binds via five atoms at once)
• Methyl (methyl), `""^(-):"CH"_3`
• Hydroxide (hydroxo), `"HO"^(-)`

The challenge is, can you keep track of which ones bind using how many electrons?