Transcript Solubility and complexes - Faculty of Science

CHEM1612 - Pharmacy
Week 8: Complexes II
Dr. Siegbert Schmid
School of Chemistry, Rm 223
Phone: 9351 4196
E-mail: [email protected]
Unless otherwise stated, all images in this file have been reproduced from:
Blackman, Bottle, Schmid, Mocerino and Wille,
Chemistry, John Wiley & Sons Australia, Ltd. 2008
ISBN: 9 78047081 0866
Complexes
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Blackman, Bottle, Schmid, Mocerino & Wille Chapters 13,10.4, 11.8
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Complex ions
Coordination compounds
Geometry of complexes
Chelates
Kstab
Solubility and complexes
Nomenclature
Isomerism in complexes
Biologically important metal-complexes
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Co(EDTA)-
Lecture 22-3
Nomenclature I
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
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Name the ligands then the metal, all in same word.
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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
Lecture 22-4
Nomenclature II
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Oxidation state in Roman numeral in parentheses after name of metal
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e.g. [Ag(NH3)2]NO3 diamminesilver(I) nitrate
Anionic ligands end in '-ido‘:
(Please modify accordingly
pp.518-519 of your book)
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Ligand Name
Fluorido
Chlorido
Bromido
Iodido
Cyanido
Hydroxido
Formula
FClBrICNOH-
Neutral ligands named as molecule, except those listed here:
Ligand Name
Ammine
Aqua
Carbonyl
Nitrosyl
Formula
NH3
H2O
CO
NO
Lecture 22-5
Nomenclature of Ligands
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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
Lecture 22-6
Nomenclature - Exercises
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[Co(H2O)6]CO3
hexaaquacobalt(II) carbonate
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[Cu(NH3)4]SO4
tetraamminecopper(II) sulfate
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(NH4)3[FeF6]
ammonium hexafluoridoferrate(III)
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K4[Mn(CN)6]
potassium hexacyanidomanganate(II)
Lecture 22-7
Assigning oxidation numbers
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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(?)
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[Mn(CN)6]4-
(CN) is -1 overall
O.N. + 6x(-1) = -4
(sum of O.N.s = overall charge)
ON = +2
Lecture 22-8
Isomerism in Complexes
Complexes can have several types of isomers:
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Structural Isomers: different atom connectivities
1.
Coordination sphere isomerism
Linkage isomerism
2.
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3.
4.
Stereoisomers: same atom connectivities but different
arrangement of atoms in space
Geometric isomerism
Optical isomerism
Lecture 22-9
Coordination Isomers
Ligands and counter-ions exchange place:
Example:
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[Pt(NH3)4Cl2](NO2)2 tetraamminedichloridoplatinum(IV) nitrite
ligands
counterions
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[Pt(NH3)4(NO2)2]Cl2 tetraamminedinitritoplatinum(IV) chloride
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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+
Lecture 22-10
Linkage isomers

Occur when a ligand has two alternative donor atoms.
S
thiocyanate ion
cyanate ion
C
O
C
N
N
thiocyanato NCS:→
isothiocyanato SCN:→
cyanato NCO:→
isocyanato OCN:→
2+
2+
NH3
H3N
H3N
Co
NH3
NH3
N
C
S
and
NH3
Pentaammineisothiocyanatocobalt(III)
H3N
H3N
Co
NH3
S
C
N
NH3
pentaamminethiocyanatocobalt (III)
Lecture 22-11
Stereoisomers: Geometric Isomers
cisplatin –
highly effective
anti-tumour agent
No
anti-tumour
effect
Lecture 22-12
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Square planar complex. Four coordinate: cis- and trans-[Pt(NH3)2Cl2]
Stereoisomers: Geometric Isomers
Octahedral complex. Six coordinate: cis- and trans- [Co(NH3)4Cl2]+
2 Cl next to
each other
2 Cl axial to
each other
violet
green
Lecture 22-13
Stereoisomers: Optical Isomers
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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-
Lecture 22-14
Stereoisomers: Optical isomers
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Metal atoms with tetrahedral or octahedral geometries (but not
square planar) may be chiral due to having different ligands.
For the octahedral case, several cases are possible, e.g.
1.
Complex with four ligands of two types.
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cis-[Co(NH3)4Cl2]+
Has no optical Cl
isomers
H3N
Cl
+ NH3
Co
NH3
NH3
cis-[Co(en)2Cl2]+
Cl
H2N
Cl
+ NH2
Co
NH2
NH2
Has optical
isomers
Lecture 22-15
Stereoisomers: Optical isomers
Having three bidentate ligands of only
one type - gives a propeller-type structure.
2.
[M(en)3]n+ complexes have optical isomers:
H2N
NH2
3+ NH2
Co
NH2
NH2
H2N
H2N
H2N
www.pt-boat.com
NH2
3+ NH2
Co
NH2
NH2
Not
superimposable
Mirror
plane
Lecture 22-16
Octahedral complex - stereoisomerism
CisFigure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Dichlorido
Bis(ethylendiamine)cobalt(III) ion
Mirror
image
rotation of I by 180° gives III ≠ II
Lecture 22-17
Octahedral complex - stereoisomerism
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
TransDichlorido
Bis(ethylendiamine)cobalt(III) ion
Mirror
image
rotation of I by 270° gives III = II
Lecture 22-18
Biologically Important Complexes
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Many biomolecules contain metal ions that act as Lewis acids.
Give some examples of naturally occurring complexes.
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Heme
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Chlorophyll
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Vitamin B12
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Enzyme Carbonic anhydrase
Lecture 22-19
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
Myoglobin protein
Blackman Figure 13.37
Lecture 22-20
Chlorophyll
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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.
Lecture 22-21
Vitamin B12
Dorothy Crowfoot Hodgkin
The Nobel Prize in Chemistry 1964
Image download from Wikipedia
Nobelprize.org
Lecture 22-22
Carbonic anhydrase
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).
Figure downloaded from Wikipedia
CO2(g) + 2H2O(l)
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.
H3O+(aq) + HCO3- (aq)
Lecture 22-23
Summary
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Concepts:
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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
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Complex Formation
Equilibria in solution: complex formation + solubility
Lecture 22-24
Question
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Does the square planar complex ion [Pt(NH3)(N3)BrCl]- have optical
isomers?
NH 3
Br
H 3N
Pt
Cl
Br
Pt
N=N=N
N=N=N
Cl
This complex has no optical isomers because it can be superimposed
on its mirror image.
Lecture 22-25
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
Coordination compounds
Coordination
Compound
Complex
Ion
Counter
Ions
Lecture 22-26
Complex Formation and solubility
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Metal complex formation can influence the solubility of a compound.
e.g.
This
AgCl(s) + 2 NH3
[Ag(NH3)2]+ + Cl-
occurs in 2 stages:
AgCl(s)
Ag+ + ClAg+ + 2 NH3
[Ag(NH3)2]+
(1)
(2)
Complex formation removes the free Ag+ from solution and so drives
the dissolution of AgCl forward.

Lecture 22-27
Solubility of AgBr in Ammonia
1.0 M NH3
AgBr(s)
Kstab(Ag(NH3)2+)= 1.7·107)
(1)
Ag+(aq) + Br-(aq)
Ag+(aq) + 2NH3(aq)
[Ag(NH3)2]+(aq)
AgBr(s) + 2NH3(aq)
[AgNH3]+(aq) + Br-(aq)
Initial Conc.
Change
Equilibrium Conc.
0
+x
x
1.0 M
-2x
1.0 - 2x
Koverall = Ksp x Kstab =
[Ag(NH3)2+][Br-]
(2)
(1)+(2)
0
+x
x
= 5.0·10-13 x 1.7·107 = 8.5·10-6
[NH3]
Substitute: Koverall = x2/(1.0-2x)2 = 8.5·10-6
x = 2.9·10-3 M
Solubility of AgBr in NH3 is 2.9·10-3 M (c.f. in thiosulfate 0.45 M)
Lecture 22-28
Linkage Isomers
NO2-
nitro O2N:→
nitrito ONO:→
O
O
Figure from Silberberg, “Chemistry”, McGraw Hill, 2006.
O
N
N
O
[Co(NH3)5(NO2)]Cl2
[Co(NH3)5(ONO)]Cl2
Pentaamminenitrocobalt(III) chloride
Pentaamminenitritocobalt(III) chloride
Lecture 22-29