1. CHEM1612 - Pharmacy Week 8: Complexes I
Dr. Siegbert Schmid
School of Chemistry, Rm 223
Phone:

2. Unless otherwise stated, all images in this file have been reproduced from:
Blackman, Bottle, Schmid, Mocerino and Wille,      Chemistry, John Wiley & Sons Australia, Ltd      ISBN:

3. Complexes Blackman Chapter 13 and Sections 10.4, 11.8
Biologically important metal-complexes
Complex ions
Kstab
Coordination compounds
Chelates
Geometry of complexes
Solubility and complexes
Nomenclature
Isomerism in complexes
Co(EDTA)-
[Cu(EDTA)]2- ion

4. Metal Ions as Lewis Acids
Whenever a metal ion enters water, a complex ion forms with water as the ligand.
Metal ions act as Lewis acid (accepts electron pair).
Water is the Lewis base (donates electron pair).
M2+
H2O(l)
[M(H2O)4]2+
adduct
M2+(aq)
(Hydrated M2+ ion)
When a metal ion enters water, a complex ion forms, with water as the ligand = hydrated cation.
Previously shown as M2+(aq)
Metal ion = Lewis acid (accepts an e- pair)
Ligand (water) = lewis base (donates e- pair)
A + :B > A:B
Ligand = species which donates the e- pair to the metal.

5. Complex Ions
Definition: A central metal ion covalently bound to two or more anions or molecules, called ligands.
Neutral ligands e.g.: water, CO, NH3
Ionic ligands e.g.: OH-, Cl-, CN-
[Ni(H2O)6]2+, a typical complex ion.
Ni2+ is the central metal ion
Six H2O molecules are the ligands
overall 2+ charge.
Blackman Figure 13.12

6. Coordination Compounds
They consist of:
Complex ion (metal ion with attached ligands)
Counter ions (additional anions/cations needed for zero net charge)
Eg. [Co(NH3)6]Cl3 (s) [Co(NH3)6]3+(aq) + 3 Cl-(aq)
Complex ion
Counter ions
In water coordination compounds behave like electrolytes: the complex ion exists as the cation and the 3 Cl- ions are separate.
Note: the counter ion may also be a complex ion.
NB square brackets indicates the complex ion and the three Cl- ions are the counter ions. There are 6 NH3 ligands. When dissolved in water, the complex exists as the cation and the 3 Cl- ions are separate.
Counter ion may also be a complex ion.
e.g. [Co(H2O)6][CoCl4]3 (s) [Co(H2O)6]3+(aq) + 3 [CoCl4]-(aq)

7. Coordination compounds
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Ligands within the coordination sphere remain bound to the metal ion
Coordination compounds {shown here as models (top), perspective drawings (middle) and chemical formulae (bottom)} typically consist of a complex ion and counter ions to neutralise the charge. The complex ion has a central metal ion surrounded by ligands.
As shown in blue,
When solid Co(NH3)6]Cl3 dissolves, the complex ions and the counter ions separate, but the ligands remain bound to the metal ion. Six ligands around the metal ion give the complex ion an octahedral geometry.
The ligands within the complex ion are said to be within the coordination sphere while the counter ions are outside.
Explain that the ligands in the coordination sphere remain bound to the metal ion.
Coordination
Compound
Complex
Ion
Counter
Ions

8. Complex Ions e.g. Ag+(aq) + 2 NH3 Ag(NH3)2+(aq)
Ligands must have a lone pair to donate to the metal.
The ‘donation’ of the electron pair is sometimes referred to as a “dative” bond.

9. Acidity of Aqueous Transition Metal Ions
A small and multiply-charged metal ion acts as an acid in water, i.e. the hydrated metal ion transfers an H+ ion to water.
Acidic
solution
The acidic behaviour of the hydrated Al3+ ion.
When a metal ion enters water, it is hydrated as water molecules bond to it. If the ion is small and multiply charged, as is the Al3+ ion, it pulls sufficient electron density from the O-H bonds of the attached water molecules to make the bonds more polar and an H+ ion is transferred to a nearby water molecule.
Hydrated iron ion – is a weak polyprotic acid. Not a ligand exchange but an acid-base reaction – breaking O-H bond so that bound H2O releases a proton and becomes a bound OH- ion.
5 bound H2O molecules
1 bound OH-
(overall charge reduced by 1)
6 bound H2O molecules
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

10. Metal Ion Hydrolysis
Each hydrated metal ion that transfers a proton to water has a characteristic Ka value.
ACID STRENGTH
Free Ion
Hydrated Ion Ka
Fe3+
Fe(H2O)63+(aq)
6 x 10-3
Cr3+
Cr(H2O)63+(aq)
1 x 10-4
Al3+
Al(H2O)63+(aq)
1 x 10-5
Be2+
Be(H2O)42+(aq)
4 x 10-6
Cu2+
Cu(H2O)62+(aq)
3 x 10-8
Fe2+
Fe(H2O)62+(aq)
4 x 10-9
Pb2+
Pb(H2O)62+(aq)
3 x 10-9
Zn2+
Zn(H2O)62+(aq)
1 x 10-9
Co2+
Co(H2O)62+(aq)
2 x 10-10
Ni2+
Ni(H2O)62+(aq)
1 x 10-10
Ka values of some hydrated metal ions (25°C).

11. Coordination number
The number of ligand atoms attached to the metal ion is called the coordination number.
varies from 2 to 8 and depends on the size, charge, and electron configuration of the metal ion.
Typical coordination numbers for some metal ions are:
M+ Coord no. M2+ Coord no. M3+ Coord no. Cu+ 2,4 Mn2+ 4,6 Sc3+ 6 Ag+ 2 Fe2+ 6 Cr3+ 6 Au+ 2,4 Co2+ 4,6 Co Ni2+ 4,6 Au Cu2+ 4, Zn2+ 4,6

12. Coordination Number and Geometry
Remember Valence Shell Electron Pair Repulsion Theory (VSEPR)? : : F : : : : F : : F : S : F : : F : : : : F :
Blackman Chapter 5 :

13. Coordination geometry
Coordination Number and Geometry
Coordination number
Coordination geometry 2
linear 4
square planar
tetrahedral 6
octahedral
Examples
[Ag(NH3)2]+
[AuCl2]-
[Pd(NH3)4]2+
[PtCl4]2-
[Zn(NH3)4]2+
[CuCl4]2-
[Co(NH3)6]3+
[FeCl6]3-

14. Ligands
Ligands that can form 1 bond with the metal ion are called monodentate (denta – tooth) e.g. H2O, NH3, Cl- (a single donor atom).
Some ligands have more than one atom with lone pairs that can be bonded to the metal ion – these are called CHELATES (greek: claw)
Bidentate ligands can form 2 bonds
e.g. ethylenediamine
Polydentate ligands – can form more than 2 bonds
e.g. EDTA - (hexadentate, can form 6 bonds)
Ligands - molecules (e.g., H2O), ions (e.g., Cl¯) or molecular
ions (e.g., acetate, CH3CO2¯) co-ordinated to the transition metal
Ligands are classified in terms of the number of donor atoms or Teeth that each uses to bond to the central metal ion.
Monodentate (latin, one-toothed) – use a single donor atom
Bidentate – use two donor atoms
Polydentate more than two donor atoms
TRIDENTATE, TETRADENTATE, PENTADENTATE, HEXADENTATE ETC.
Remove entrance bits for handout!

15. Bidentate chelate ligands
MX+(en)
Ethylenediamine (en) has two N atoms that can form a bond with the metal ion, giving a five-membered ring.
Chelates – from greek for crab’s claw
Bidentate and polydentate ligands give rise to rings in the complex ion.
Ethylenediamine (abbrev en) has a chain of 4 atoms and 2 donor atoms so it forms a five-membered ring with the two electron donating N atoms bonding to the metal atom.
GRABBING IONS – Because it has 6 donor atoms, the ethylenediaminetetraacetate (EDTA4-) ion forms very stable complexes with many metal ions.. This property makes EDTA useful in treating heavy-metal poisoning. Once ingested by the patient, the ligand acts as a scavenger to remove lead and other heavy metal ions from the blood and other bodily fluids. N=blue, O=red, metal=green
Blackman, Bottle, Schmid, Mocerino & Wille, Figure 13.10

16. Hexadentate ligand: EDTA
Ethylenediaminetetraacetate tetraanion (EDTA4-)
EDTA forms very stable complexes with many metal ions. EDTA is used for treating heavy-metal poisoning, because it removes lead and other heavy metal ions from the blood and other bodily fluids.
Co(III)
N=blue
O=red
GRABBING IONS – Because it has 6 donor atoms, the ethylenediaminetetraacetate (EDTA4-) ion forms very stable complexes with many metal ions..
Very IMPORTANT ligand in chemical analysis and in medicine.
This property makes EDTA useful in treating heavy-metal poisoning. Once ingested by the patient, the ligand acts as a scavenger to remove lead and other heavy metal ions from the blood and other bodily fluids. N=blue, O=red, metal=green
Administered as [Ca(EDTA)]2-
Since Pb2+ displaces Ca2+ from bone, lead poisoning is treated with [Ca(EDTA)]2-
[Ca(EDTA)]2- + Pb2+ <> Ca2+ + [Pb(EDTA)]2-
Pb2+ displaces Ca2+ from [Ca(EDTA)]2- and Ca2+ is deposited in bone.
[Co(EDTA)]-

17. Examples of ligands Some common ligands in coordination compounds
Each ligand has one or more donor atoms shown in blue.
May be neutral or negatively charged (red circles).
Table from Silberberg, “Chemistry”, McGraw Hill, 2006.

18. Examples of ligands
The charge of a complex ion is the charge of the metal ion plus the charge of its ligands:
e.g. [Ni(H2O)6]2+ charge of complex ion is that of the Ni2+ ion.
eg [NiCl4]2- Ni2+ ion coordinated to four chloride (Cl-) ions giving overall (2-) charge.
Chelates – from greek for crab’s claw
Bidentate and polydentate ligands give rise to rings in the complex ion.
Ethylenediamine (abbrev en) has a chain of 4 atoms so it forms a five-membered ring with the two electron donating N atoms bonding to the metal atom.
GRABBING IONS – Because it has 6 donor atoms, the ethylenediaminetetraacetate (EDTA4-) ion forms very stable complexes with many metal ions.. This property makes EDTA useful in treating heavy-metal poisoning. Once ingested by the patient, the ligand acts as a scavenger to remove lead and other heavy metal ions from the blood and other bodily fluids. N=blue, O=red, metal=green
[Fe(H2O)6]3+
[Fe(en)3]3+
[Fe(EDTA)]-
monodentate
ligands
bidentate
ligands
hexadentate
ligands

19. Lewis bases: water and ammonia
M(H2O)42+
The stepwise exchange of NH3 for H2O in M(H2O)42+.
NH3
3NH3 3
more
steps
M(H2O)3(NH3)2+
M(NH3)42+
When a metal ion enters water, a complex ion forms, with water as the ligand = hydrated cation(top left).
Add another ligand eg NH3– the bound water molecules exchange for the other ligand – stepwise.
NH3 molecules replace the bound H2O molecules one at a time to form the M(NH3)42+ ion.
Ammonia is a stronger Lewis base than water
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.

20. Equilibrium Constant Kstab
Metal Ion + nLigand Complex
The larger Kstab, the more stable the complex, e.g.
The complex formation equilibrium is characterised by a stability constant, Kstab (also called formation constant):
Ag+(aq) + 2 NH3 Ag(NH3)2+(aq)
Sounds vicious – is another equilibrium constant called the stability constant.
Just going to say this, might not make much sense yet, but we’ll do a couple fo examples to try and give you better idea of what it meants, instead of just showering you with anpother equation.

21. Stepwise stability constant
Metal ions gain ligands one at a time.
Each step characterised by “stepwise stability constant” aka “stepwise formation constant”. Overall formation constant = Kstab = K1 x K2…x Kn
Example:
Ag+(aq) NH3(aq) Ag(NH3)+(aq) K1 = 2.1 · 103
Ag(NH3)+(aq) + NH3(aq) Ag(NH3)2+(aq) K2 = 8.2 · 103
Ag+(aq) NH3(aq) Ag(NH3)2+(aq) Kstab =
Kstab = K1 x K2 = [Ag(NH3)2+] = 1.7 · 107
[Ag+] [NH3]2
Sounds vicious – is another equilibrium constant called the stability constant.
Just going to say this, might not make much sense yet, but we’ll do a couple fo examples to try and give you better idea of what it means, instead of just showering you with another equation.

22. Demo: Nickel complexes
Ni2+ forms three complexes with ethylenediamine:
Mix [Ni(H2O)6]2+ and en in ratio 3:1 → some [Ni(en)(H2O)4]2+and [Ni(H2O)6]2
Green blue-green
Mix [Ni(H2O)6]2+ and en in ratio 1:1 → mostly [Ni(en)(H2O)4]2+
light blue
Mix [Ni(H2O)6]2+ and en in ratio 1:3 → mostly [Ni(en)3] purple
Demo 9.7 Nickel complexes – will see stepwise formation of different complexes with ethylenediamine.
Solutions of Nickel(II)chloride and 1,2-ethylenediamine are prepared and added to one another in three different ratios. These additions result in 3 solutions with 3 different colours.

23. Biologically Important Complexes
Many biomolecules contain metal ions that act as Lewis acids.
Give some examples of naturally occurring complexes.
Heme
Chlorophyll
Vitamin B12
Enzyme Carbonic anhydrase

24. Heme
O2 bound
to Fe2+
Heme is a square planar complex of Fe2+ and the tetradentate ring ligand porphyrin (bonds to 4 donor N atoms).
Present in hemoglobin, which carries oxygen in blood, and myoglobin, which stores oxygen in muscle.
Porphyrin ring
Iron plays a crucial role in oxygen transport in all vertebrates – let’s see how this involves complexes.
Heme is a porphyrin – a complex derived from a metal ion and the tetradentate ring ligand known as porphin.
Fe(II) is centered in the plane – tetradentate, square planar complex (covalent bonds to 4 donor N atoms). Look at formula and model.
Hemoglobin – the oxygen transporting protein, consists of 4 folded protein chains called globins.
Shown are the four protein chains (2 yellow, 2 pink), each with a bound heme (shown in red) complexed to Fe (white).
When heme is bound in hemoglobin, the complex is octahedral – a nearby amino acid N provides the 5th ligand (not shown at bottom diagram) and the sixth ligand is an O atom from either an O2 (shown) or and H2O molecule.
Hemoglobin exists in two forms depending on the nature of the sixth ligand.
Fe2+ bound octahedrally. If not o2 and oxyhemoglobin, then water and deoxyhemoglobin. CO toxic bec binds 200 times more tightly than O2, so interferes with oxygen transport.
In the blood vessels of the lungs (high O2 concentration) heme binds to O2 and forms oxyhemoglobin (RHS). Then transported in the arteries to O2 depleted tissues where O2 is released and replaced by an H2O molecule to form deoxyhemoglobin.
Heme
Hemoglobin and the octahedral complex in heme.
Myoglobin protein
Blackman Figure 13.37

25. Chlorophyll Chlorophyll is a photosynthetic pigment, that
gives leaves the characteristic green colour.
It is a complex of Mg2+ and a porphyrin ring system (four N atoms are the chelae).
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Chlorophyll – discussed when learnt about Lewis Acids? Mg2+ ion is a lewis acid in the chlorophyll molecule.
We all know about chlorophyll, very important for photosynthesis, and where would we be without green plants.
Chlorophyll is the molecule that absorbs sunlight and uses its energy to synthesise carbohydrates from CO2 and water. This process is known as photosynthesis and is the basis for sustaining the life processes of all plants. Since animals and humans obtain their food supply by eating plants, photosynthesis can be said to be the source of our life also.
Chlorophyll is the molecule that traps this light energy - and is called a photoreceptor. It is found in the chloroplasts of green plants, and is what makes green plants, green. The basic structure of a chlorophyll molecule is a porphyrin ring, co-ordinated to a central atom. This is very similar in structure to the heme group found in hemoglobin, except that in heme the central atom is iron, whereas in chlorophyll it is magnesium.
Vitamin B12 has a similar structure with a central Co3+.
Chlorophyll absorbs strongly in the blue and red regions reflecting mostly green wavelengths into your eyes.

26. Dorothy Crowfoot Hodgkin
Vitamin B12
Dorothy Crowfoot Hodgkin
The Nobel Prize in Chemistry 1964
Nobelprize.org
Vitamin B12 has a similar structure with a central Co3+.
Crowfoot = maiden name
determined the structure of vitamin B12 in 1956 by X-ray crystallographic techniques after 8 years work on it.. Had previously been involved in solving the structure of penicillin and in establishing that DNA was a double helix. Solved the structure of insulin in 1969.
Never before had it been possible to determine the exact structure of so large a molecule, and the result has been seen as a triumph for X-ray crystallographic techniques.
This vitamin can be synthetized by certain bacteria and fungi, of which some play an active part in the digestive processes of animals. The production of B12 is most pronounced in the ruminants, who seem to require this vitamin in particularly large amounts. In most of the other higher animals, for example in man, the production of B12 is small, and their food must therefore contain sufficient quantities of ready-made B12. Lack of B12 in the diet, or a reduced ability to absorb this vitamin via the walls of the alimentary canal, leads in man to the fatal blood condition of pernicious anaemia. The illness can always be arrested by injections of B12 which is only needed in very small quantities.
Image download from Wikipedia

27. Carbonic anhydrase CO2(g) + 2H2O(l) H3O+(aq) + HCO3- (aq)
Tetrahedral complex of Zn2+.
Catalyses reaction between water and carbon dioxide during respiration. Coordinated to 3 N, fourth site left free to interact with molecule whose reaction is being catalysed (here with water).
By withdrawing electron density, makes water acidic to lose proton and OH- attacks partial positive C of CO2 much more vigorously. Cd2+ is toxic because it competes with zinc for this spot.
Figure downloaded from Wikipedia
Tetrahedral zinc, cn 4. catalyses reaction between water and carbon dioxide during respiration. Coorded to 3 N, fourther left free to interact with moelcule whose reaction is being catalysed. (accepts lone pair, is lewis acid, here with water. By withdrawing electron density, makes water acidic to lose proton resulting bound Oh- attacks partial positive C of co2 much more vigourously and rxn rate is higher. Cd2+ is toxic because it competes with zinc for this spot.
Interesting story re Cd3+, 6+ in uni news sprts supplement. Fourth floor end of corridor.
Here’s Cd 2+, but also exist Cd3+ and 6+. Cd3+ is the form you get in sports supplements
Also:
Zinc – many enzymes including carbonic anhydrase, carboxypeptidase A, alcohol dehydrogenase
Cobalt – xylose isomerase, cobalamin (vitamin B12)
Manganese, Chromium, Vanadium...
CO2(g) + 2H2O(l) H3O+(aq) + HCO3- (aq)

28. (careful with the direction of the equation represented by Kstab!)
Exercise
0.01 moles of AgNO3 are added to a 500 mL of a 1.00 M solution of KCN. Then enough water is added to make 1.00 L of solution. Calculate the equilibrium [Ag+] given Kstab [Ag(CN)2]– =1020 M–2.
(careful with the direction of the equation represented by Kstab!)
Ag CN– [Ag(CN)2]–
initial /M
change ~
equilibrium /M x
Don’t include this page in the handout. Has animations which uncover things…
EKIASC
Equation
K expression
ICE
Assumptions
Substitute
Check

29. Complex Formation and solubility
Metal complex formation can influence the solubility of a compound.
e.g. AgCl(s) + 2 NH [Ag(NH3)2]+ + Cl-
This occurs in 2 stages:
AgCl(s) Ag+ + Cl- (1)
Ag+ + 2 NH [Ag(NH3)2]+ (2)
Complex formation removes the free Ag+ from solution and so drives the dissolution of AgCl forward.

30. Complex ion formation affects solubility
Example: AgBr(s) Ag+(aq) + Br-(aq)
Calculate the solubility of AgBr in:
a) water
b) 1.0 M sodium thiosulfate (Na2S2O3)
c) 1.0 M NH3
(Ksp (AgBr)= 5.0·10-13, Kstab ([Ag(S2O3)2]3- )= 4.7·1013; Kstab(Ag(NH3)2+)= 1.7·107)
a) Solubility of AgBr in water
Ksp = [Ag+][Br-]
AgBr(s) Ag+(aq) + Br-(aq)
Back to our discussion of complexes from last lecture….
Application from black and white film developing
-excess AgBr is removed from the film by “hypo” an aqueous solution of thiosulfate which forms the complex ion Ag(S2O3)23-. x x
Ksp = x2 = 5.0· x = 7.1 ·10-7 M

31. b) Solubility of AgBr in sodium thiosulfate
1.0 M Na2S2O3
(1)
AgBr(s) Ag+(aq) + Br-(aq)
Ag+(aq) + 2S2O32-(aq) [Ag(S2O3)2]3-(aq)
AgBr(s) + 2S2O32-(aq) [Ag(S2O3)2]3-(aq) + Br-(aq)
(2)
(1)+(2)
1.0 M
-2x
1.0 -2x +x x
Initial Conc.
Change
Equilibrium Conc. +x x
Koverall = Ksp x Kstab = = 5.0·10-13 x 4.7·1013 = 24
[Ag(S2O3)23-][Br-]
[S2O32-]2
Sodium thiosulfate - used as a photographic fixing agent and as a bleach. Also called hypo, hyposulfite
In hypo, Ag+ forms a complex ion with S2O32- which shifts the equilibrium and dissolves more AgBr.
Write the complex ion equation and add it to the equation for dissolving AgBr to obtain the overall equation for dissolving AgBr in hypo.
Multiply Ksp by Kstab to find Koverall.
Write Koverall in terms of concentrations on the board!!!
Substitute: Koverall = x2/( x)2 = 24 x = 0.45
Solubility of AgBr in thiosulfate is 0.45 M (c.f. in water 7.1 x 10-7 M)

32. c) Solubility of AgBr in ammonia
1.0 M NH3
(1)
AgBr(s) Ag+(aq) + Br-(aq)
Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+(aq)
AgBr(s) + 2NH3(aq) [AgNH3]+(aq) + Br-(aq)
(2)
(1)+(2)
1.0 M
-2x x +x x
Initial Conc.
Change
Equilibrium Conc. +x x
Koverall = Ksp x Kstab = = 5.0·10-13 x 1.7·107 = 8.5·10-6
[Ag(NH3)2+][Br-]
[NH3]
Sodium thiosulfate - used as a photographic fixing agent and as a bleach. Also called hypo, hyposulfite
In hypo, Ag+ forms a complex ion with S2O32- which shifts the equilibrium and dissolves more AgBr.
Write the complex ion equation and add it to the equation for dissolving AgBr to obtain the overall equation for dissolving AgBr in hypo.
Multiply Ksp by Kstab to find Koverall.
Write Koverall in terms of concentrations on the board!!!
Substitute: Koverall = x2/(1.0-2x)2 = 8.5· x = 2.9·10-3 M
Solubility of AgBr in NH3 is 2.9·10-3 M (c.f. in thiosulfate M)

33. The One Pot Reaction
Start with a AgNO3 aqueous solution. Add sequentially :
Ag+ + OH-  AgOH(s) (brown)
2 AgOH(s) + HPO42-  Ag3PO4(s) (yellow)
Ag3PO4(s) + HNO3  3Ag+ + NO3- + HPO42-
Ag+ + Cl-  AgCl (s) (white)
AgCl(s) + 2NH3  [Ag(NH3)2]+ + Cl-
[Ag(NH3)2]+ + Br-  AgBr (s)(green/white)
AgBr(s) + 2S2O32-  [Ag(S2O3)2]3- + Br-
[Ag(S2O3)2]3- + I-  AgI (s) (yellow)
AgI(s) + 2CN-  [Ag(CN)2]- + I-
2 Ag(CN) S2-  Ag2S + CN-(black)
+ NaOH
+ Na2HPO4
+ HNO3
+ NaCl
+ NH3
+ KBr
+ Na2S2O3
+ KI
+ KCN
+ Na2S
Ksp = M2
Ksp = M3
Ksp = 1.8 x M2
Kstab = 1.7 x 107 M-2
Ksp = 5 x M2
Kstab = 2.5 x 1013 M-2
Ksp = 8.3 x M2
Kstab = 6.3 x 1019 M-2
Ksp = 8 x M3
Solubility and complex ion Equilibria of silver compounds (demo 5.14)
Start with a solution of silver nitrate. Ag NO3 has no Ksp because it is so soluble - If you remember back to your solubility rules, you’ll remember that all nitrates are soluble.
So here’s an illustraion of difference in solubilities for different compounds of silver. Now, none of these contain silver, so the only silver in solution is the stuff I start with..
You can see that high Ksps (AgNO3) are soluble and low Ksps are not, they ppt out. So how high does Ksp have to be for a ppt to dissolve. Or, put it the other other way. how how dies it have to be for a ppt to form? And that’s where Q comes in.
If Q> Ksp then a precipitate is formed.
Addition of a ligand increases the solubility of a nearly insoluble ionic compound if it forms a complex ion with the cation.
Sequential addition of clear, colourless solutions alternately causes precipitation and dissolution.

34. Nomenclature Rules for nomenclature of coordination compounds:
Name cation, then anion, as separate words.
Examples:
[Pt(NH3)4Cl2](NO2)2 tetraamminedichloridoplatinum(IV) nitrite
[Pt(NH3)4(NO2)2]Cl2 tetraamminedinitritoplatinum(IV) chloride
Name the ligands then the metal, all in same word.
Number of ligands as Greek prefixes (di-, tri-, tetra-, penta-, hexa-), except ligands that already have numerical prefixes which use Latin prefixes (bis, tris, tetrakis…)
e.g. bis(ethylenediamine) for (en)2
Coordination compounds require more complex names than just cation and anion, as for simple salts.
NaCl sodium chloride
CaCl2 calcium chloride
FeCl2 iron(II) chloride
FeCl3 iron (III) chloride

35. Nomenclature II Anionic ligands end in '-ido';
Oxidation state in Roman numeral in parentheses after name of metal
e.g. [Ag(NH3)2]NO3 diamminesilver(I) nitrate
Anionic ligands end in '-ido';
Neutral ligands named as molecule, except those listed here:
Fluorido
Chlorido
Bromido
Iodido
Hydroxido
Cyanido
New IUPAC Nomenclature:
all anions ending in – ‘ide’ become -‘ido’.
(Please modify accordingly
pp of your book)

36. Nomenclature of Ligands
Ligands named in alphabetical order (but prefixes do not affect the order)
e.g. [Co(NH3)5Cl]SO4 pentaamminechloridocobalt(III) sulfate
Anionic complexes end in ‘-ate’
e.g. K3[CrCl6] potassium hexachloridochromate(III)
Some metals in anionic complexes use Latin -ate names:
Not Ironate
Not Copperate
Not Leadate
Not Silverate
Not Goldate
Not Tinnate
Prefixes do not affect the alphabetical order of the ligand names.

37. Nomenclature - Exercises
[Co(H2O)6]CO3
hexaaquacobalt(II) carbonate
[Cu(NH3)4]SO4
tetraamminecopper(II) sulfate
(NH4)3[FeF6]
ammonium hexafluoridoferrate(III)
K4[Mn(CN)6]
potassium hexacyanidomanganate(II)

38. Assigning oxidation numbers
Example 1:
Find O.N. of Co in : [Co(NH3)5Cl]SO4 pentaamminechloridocobalt(?) sulfate
[Co(NH3)5Cl]2+ ammine is neutral, chloride is -1
O.N. -1 = +2 (sum of O.N.s = overall charge)
O.N. = +3
Example 2:
Find O.N. of Mn in :K4[Mn(CN)6] potassium hexacyanidomanganate(?)
[Mn(CN)6]4- (CN) is -1 overall
O.N. + 6x(-1) = -4 (sum of O.N.s = overall charge)
ON = +2

39. About naming complexes
You won’t be asked to draw formulae of complicated biological complexes.
You should be able to use the naming rules to write formulae from names and names from formulae.

40. Isomerism in Complexes
Complexes can have several types of isomers:
Structural Isomers: different atom connectivities
Coordination sphere isomerism
Linkage isomerism
Stereoisomers: same atom connectivities but different arrangement of atoms in space
Geometric isomerism
Optical isomerism

41. Coordination compounds
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Ligands within the coordination sphere remain bound to the metal ion
Coordination compounds {shown here as models (top), perspective drawings (middle) and chemical formulae (bottom)} typically consist of a complex ion and counter ions to neutralise the charge. The complex ion has a central metal ion surrounded by ligands.
As shown in blue,
When solid Co(NH3)6]Cl3 dissolves, the complex ions and the counter ions separate, but the ligands remain bound to the metal ion. Six ligands around the metal ion give the complex ion an octahedral geometry.
The ligands within the complex ion are said to be within the coordination sphere while the counter ions are outside.
Explain that the ligands in the coordination sphere remain bound to the metal ion.
Complex
Ion
Coordination
Compound
Counter
Ions

42. Coordination Isomers Ligands and counter-ions exchange place: Example:
[Pt(NH3)4Cl2](NO2)2 tetraamminedichloridoplatinum(IV) nitrite
[Pt(NH3)4(NO2)2]Cl2 tetraamminedinitritoplatinum(IV) chloride
Two sets of ligands are reversed:
[Cr(NH3)6][Co(CN)6] NH3 is a ligand for Cr3+
[Co(NH3)6][Cr(CN)6] NH3 is a ligand for Co3+
ligands counterions
Occur when the composition of the complex ion changes but not that of the compound (mol. Formula remains the same)
-ligands and counterions change positions.
1st compound – chloride ions are the ligands, NO2- ions are counter ions.
2nd compound – roles are reversed.

43. Linkage isomers Occur when a ligand has two alternative donor atoms.
Example 1:
Thiocyanato NCS:→
Isothiocyanato SCN:→
Thiocyanate ion
cyanate ion
cyanato NCO:→
isocyanato OCN:→
Also possible for nitrite ion: nitro O2N: versus nitrito ONO:
And cyanate: cyanato NCO: versus isocyanato OCN:
Pentaammineisothiocyanatocobalt(III) pentaamminethiocyanatocobalt (III)

44. Linkage Isomers Example 2: NO2- nitro O2N:→ nitrito ONO:→
[Co(NH3)5(NO2)]Cl2
Pentaamminenitrocobalt(III) chloride
[Co(NH3)5(ONO)]Cl2
Pentaamminenitritocobalt(III) chloride
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Also possible for nitrite ion: nitro O2N: versus nitrito ONO:
And cyanate: cyanato NCO: versus isocyanato OCN:

45. Isomerism in Complexes
Complexes can have several types of isomers:
Structural Isomers: different atom connectivities
Coordination sphere isomerism
Linkage isomerism
Stereoisomers: same atom connectivities but different arrangement of atoms in space
Geometric isomerism
Optical isomerism

46. Stereoisomers: Geometric Isomers
Square planar complex. Four coordinate: cis- and trans-[Pt(NH3)2Cl2]
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
cisplatin –
highly effective
anti-tumour agent No
anti-tumour
effect
Geometrical isomers, also called cis-trans isomers or diastereomers.
Arranged differently in space relative to the central metal ion.
Square planar:
Cis – identical ligands next to each other
Trans – identical ligands across from each other
Their biological behaviours are remarkably different.
Cis isomer called cisplatin – highly effective anti-tumour agent – discovered in the 1960s, still the moost effective treatment for some kinds of cancer. Thought to bind to DNA double helix with Cl ligands replaced by a ligand on each strand of DNA – prevents DNA replication.
Trans isomer has no antitumor effect.
Octahedral complexes also exhibit cis-trans isomerism.
The cis isomer has two Cl-ligands next to each other and is violet.
The trans isomer has these two ligands across from each other and is green.

47. Stereoisomers: Geometric Isomers
Octahedral complex. Six coordinate: cis- and trans- [Co(NH3)4Cl2]+
2 Cl next to
each other
violet
Geometrical isomers, also called cis-trans isomers or diastereomers.
Arranged differently in space relative to the central metal ion.
Square planar:
Cis – identical ligands next to each other
Trans – identical ligands across from each other
Their biological behaviours are remarkably different.
Cis isomer called cisplatin – highly effective anti-tumour agent – discovered in the 1960s, still the moost effective treatment for some kinds of cancer. Thought to bind to DNA double helix with Cl ligands replaced by a ligand on each strand of DNA – prevents DNA replication.
Trans isomer has no antitumor effect.
Octahedral complexes also exhibit cis-trans isomerism.
The cis isomer has two Cl-ligands next to each other and is violet.
The trans isomer has these two ligands across from each other and is green.
2 Cl axial to
each other
green

48. Stereoisomers: Optical Isomers
When a molecule is non-superimposable with its mirror image.
Example: four different substituents about tetrahedral centre.
Same physical properties, except direction in which they rotate the plane of polarized light.
[NiClBrFI]2-

49. Stereoisomers: Optical isomers
Metal atoms with tetrahedral or octahedral geometries (but not square planar) may be chiral due to having different ligands.
For the octahedral case, several chiralities are possible, e.g.
Complex with four ligands of two types.
cis-[Co(NH3)4Cl2]+ cis-[Co(en)2Cl2]+ +
Has no optical
isomers
Has optical
Co3+ has a coordination number of 6 and an octahedral geometry.
Use models to show – mirror isomers here
Chirality
Enantiomers occur when a molecule and its mirror image cannot be superimposed. (differ in the direction they can rotate plane polarised light)
Observe by rotating one isomer and seeing if it is superimposable on the other isomer (its mirror image).
[M(en)3]n+ - no geometrical isomers are possible because all the ligands are identical (3 bidentate ligands are identical).
Explain curved abbreviation for en ligand.

50. Stereoisomers: Optical isomers
Having three bidentate ligands of only
one type - gives a propeller-type structure.
[M(en)3]n+ complexes have optical isomers:
Not
superimposable 3+
Mirror
plane
Co3+ has a coordination number of 6 and an octahedral geometry.
Use models to show – mirror isomers here
Chirality
Enantiomers occur when a molecule and its mirror image cannot be superimposed. (differ in the direction they can rotate plane polarised light)
Observe by rotating one isomer and seeing if it is superimposable on the other isomer (its mirror image).
[M(en)3]n+ - no geometrical isomers are possible because all the ligands are identical (3 bidentate ligands are identical).
Explain curved abbreviation for en ligand.

51. Octahedral complex - stereoisomerism
Cis-
Dichlorido
Bis(ethylendiamine)cobalt(III) ion
Mirror
image
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
The curved wedges in these diagrams represent the bidentate ligand ethylenediamine
NH2-CH2-CH2-NH2
Cis compound exist as enantiomers (optical isomers). I and II are not superimposable.
Trans compound does not have optical isomers, I, II and III are identical.
rotation of I by 180° gives III ≠ II

52. Octahedral complex - stereoisomerism
Trans-
Dichlorido
Bis(ethylendiamine)cobalt(III) ion
Mirror
image
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
The curved wedges in these diagrams represent the bidentate ligand ethylenediamine
NH2-CH2-CH2-NH2
Cis compound exist as enantiomers (optical isomers). I and II are not superimposable.
Trans compound does not have optical isomers, I, II and III are identical.
rotation of I by 90° gives III = II

53. Question Br Pt N=N=N N H Cl
Does the square planar complex ion [Pt(NH3)(N3)BrCl]- have optical isomers? Br Pt
N=N=N N H 3 Cl
This complex has no optical isomers because it can be superimposed
on its mirror image.

54. Summary Concepts: Calculations Complex formation
Stability constant and stepwise stability constant
Acidity of some metal ions in solution
Coordination compounds and geometry
Nomenclature of coordination compounds
Isomerism in Complexes
Calculations
Complex Formation
Equilibria in solution: complex formation + solubility