Ligands

Question 1

what are ligands?

Answer 1

molecules or ions that act as a Lewis base (an electron pair donor)

• have one or more atom donors that donate lone pairs
• neutral such as H2O and NH3
• anionic such as Cl- or CN-

Question 2

deticity

Answer 2

way of classifying ligands by number of donor atoms attached to a metal centre 
mono dentate (one donor atom), bidentate (two), trident ate (three)

Question 3

neutral monodentate

Answer 3

H2O, NH3, CO

Question 4

anionic mono dentate

Answer 4

F-, Cl-, OH-

Question 5

mono dentate ligands with multiple donor atoms

Answer 5

CN-, SCN-, NO2- (both donor atoms cannot bind with the metal cation at the same time)

Question 6

bidentate ligands

Answer 6

• ethylenediamine (en) forms a chelate ring (more stable than mono dentate and increases entropy most)
• oxalate
  symmetrical or not

Question 7

trident ate ligands

Answer 7

diethylenetriamine

Question 8

polydentate ligands

Answer 8

one type are macrocyclic ligands - large, ring-shaped molecules

Question 9

riding ligands

Answer 9

coordinate to multiple metals
one donor atom with multiple lone pairs or multiple donor atoms

examples: OH-, O2-, F-, Cl-, CN-, SCN-

Question 10

aqua (H2O) complexes

Answer 10

first row transition metals dissolve in water to form complexes with water or OH- ligands

Question 11

hydroxido complexes

Answer 11

metal ions are Lewis acids
some are very strong (Fe3+, Ti3+ - related to Zeff and increases left to right)
if strong, the solution becomes a Bronsted acid (donates H+)
electrons are drawn from the aqua ligand so that it dissociates
solution becomes acidic

Question 12

chlorido complexes

Answer 12

reaction of metal aqua complexes with Cl- to form tetrahedral chloride complexes
bromide and iodine act the same
octahedral becomes tetrahedral (because of size of halide ligands and charge repulsion) which causes a colour change

Question 13

cyanido complexes

Answer 13

CN- usually binds through the C but can bind with both by bridging
can form a coordination polymer (looks like a lattice)

Question 14

ammine complexes

Answer 14

aqueous ammonia + a metal (OH2)6 complex displaces aqua ligands and makes a metal ammine and water

Question 15

ligand exchange and stability constant and Gibbs

Answer 15

ligand exchange occurs in an equilibrium
counter ions like spectator ions do not need to be considered
consider the exchange in steps (each exchange happens one at a time) - 4 equations for 4 constants
then a Kf or stability/formation constant can be calculated
higher Kf = more stable

Gibbs free energy: negative in the forwards direction

Question 16

naming coordination compounds

Answer 16

in formulas and full names we place the ligands in alphabetical order
anions with -ide become -ido as ligands
anions with ate become -ato as ligands

potassium hexaaquacobolt (II)

cation is first, ligands are alphabetical (ignore hex or numbering), state of metal is included and in formula (OH2) the donor atom is written first (not H2O)

Question 17

ligands with multiple potential donor atoms

Answer 17

write the one that is the donor first in formula SCN or NCS

in the written name, put a small -kS- called kappa notation

Question 18

naming anionic complexes

some names

Answer 18

if metal complex is overall negative in charge, add the suffix -ate

some names: ferrate, plumbate, aurate, cuprate, argentate, stannate