List examples of positive and negative ligands?

2 Answers
Aug 23, 2017

Answer:

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.

Aug 23, 2017

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?