CHEM1612 - Pharmacy Week 8: Complexes II

Dr. Siegbert Schmid School of Chemistry, Rm 223 Phone: 9351 4196 E-mail: siegbert.schmid@sydney.edu.au

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

Lecture 22-3

Complexes

n  Blackman, Bottle, Schmid, Mocerino & Wille Chapters 13,10.4, 11.8

n  Complex ions n  Coordination compounds n  Geometry of complexes n  Chelates n  Kstab n  Solubility and complexes n  Nomenclature n  Isomerism in complexes n  Biologically important metal-complexes

Co(EDTA)-

Lecture 22-4

Rules for nomenclature of coordination compounds: n  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

n  Name the ligands then the metal, all in same word.

n  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…) q  e.g. bis(ethylenediamine) for (en)2

Nomenclature I

Lecture 22-5

Nomenclature II n  Oxidation state in Roman numeral in parentheses after name of metal

q  e.g. [Ag(NH3)2]NO3 diamminesilver(I) nitrate

n  Anionic ligands end in '-ido‘:

n  Neutral ligands named as molecule, except those listed here:

(Please modify accordingly

pp.518-519 of your book)

Ligand Name Formula Fluorido F- Chlorido Cl- Bromido Br- Iodido I- Cyanido CN- Hydroxido OH-

Ligand Name Formula Ammine NH3 Aqua H2O Carbonyl CO Nitrosyl NO

Lecture 22-6

n  Ligands named in alphabetical order (but prefixes do not affect the order) q  e.g. [Co(NH3)5Cl]SO4 pentaamminechloridocobalt(III) sulfate

n  Anionic complexes end in ‘-ate’ q  e.g. K3[CrCl6] potassium hexachloridochromate(III)

n  Some metals in anionic complexes use Latin -ate names:

Nomenclature III

Not Ironate Not Copperate Not Leadate Not Silverate Not Goldate Not Tinnate

Lecture 22-7

Nomenclature - Exercises

n  [Co(H2O)6]CO3 hexaaquacobalt(II) carbonate

n  [Cu(NH3)4]SO4

tetraamminecopper(II) sulfate n  (NH4)3[FeF6]

ammonium hexafluoridoferrate(III) n  K4[Mn(CN)6]

potassium hexacyanidomanganate(II)

Lecture 22-8

n  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

Assigning oxidation numbers

n  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

Lecture 22-9

Isomerism in Complexes Complexes can have several types of isomers:

n  Structural Isomers: different atom connectivities

1.  Coordination sphere isomerism 2.  Linkage isomerism

n  Stereoisomers: same atom connectivities but different arrangement of atoms in space

3.  Geometric isomerism 4.  Optical isomerism

Lecture 22-10

Coordination Isomers n  Ligands and counter-ions exchange place: Example: n  [Pt(NH3)4Cl2](NO2)2 tetraamminedichloridoplatinum(IV) nitrite

n  [Pt(NH3)4(NO2)2]Cl2 tetraamminedinitritoplatinum(IV) chloride

n  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

Lecture 22-11

Linkage isomers n  Occur when a ligand has two alternative donor atoms.

NCSthiocyanate ion

H3N Co

NH3

NH3

NNH3

H3NC S

2+

H3N Co

NH3

NH3

SNH3

H3NC N

2+

and

cyanate ion NCOcyanato NCO:→ isocyanato OCN:→

thiocyanato NCS:→ isothiocyanato SCN:→

Pentaammineisothiocyanatocobalt(III) pentaamminethiocyanatocobalt (III)

Lecture 22-12

Square planar complex. Four coordinate: cis- and trans-[Pt(NH3)2Cl2]

Stereoisomers: Geometric Isomers

No

anti-tumour

effect

cisplatin –

highly effective

anti-tumour agent

Figure from S

ilberberg, “Chem

istry”, McG

raw H

ill, 2006.

Lecture 22-13

Stereoisomers: Geometric Isomers

2 Cl next to each other

Octahedral complex. Six coordinate: cis- and trans- [Co(NH3)4Cl2]+

violet

green 2 Cl axial to each other

Lecture 22-14

[NiClBrFI]2-

Stereoisomers: Optical Isomers

n  When a molecule is non-superimposable with its mirror image. n  Example: four different substituents about tetrahedral centre. n  Same physical properties, except direction in which they rotate the

plane of polarized light.

Lecture 22-15

cis-[Co(NH3)4Cl2]+ cis-[Co(en)2Cl2]+

ClCo

NH3

NH3H3N

Cl

NH3

ClCo

NH2

NH2H2N

Cl

NH2

+ + Has no optical

isomers

Has optical

isomers

Stereoisomers: Optical isomers n  Metal atoms with tetrahedral or octahedral geometries (but not

square planar) may be chiral due to having different ligands. n  For the octahedral case, several cases are possible, e.g.

1.  Complex with four ligands of two types.

Lecture 22-16

[M(en)3]n+ complexes have optical isomers:

Not superimposable

H2N CoNH2

NH2H2N

NH2

NH2

NH2Co

NH2

NH2 NH2

H2N

H2N

3+ 3+

Mirror plane

Stereoisomers: Optical isomers

2.  Having three bidentate ligands of only one type - gives a propeller-type structure.

www.pt-boat.com

Lecture 22-17

Octahedral complex - stereoisomerism

rotation of I by 180° gives III ≠ II

Mirror

image

Cis-

Dichlorido

Bis(ethylendiamine)cobalt(III) ion

Figure from S

ilberberg, “Chem

istry”, McG

raw H

ill, 2006.

Lecture 22-18

Octahedral complex - stereoisomerism

rotation of I by 270° gives III = II

Mirror

image

Trans-

Dichlorido

Bis(ethylendiamine)cobalt(III) ion

Figure from S

ilberberg, “Chem

istry”, McG

raw H

ill, 2006.

Lecture 22-19

Heme

Heme is a square planar complex of Fe2+ and the tetradentate ring l igand porphyrin (bonds to 4 donor N atoms). Present in hemoglobin, which carries oxygen in blood, and myoglobin, which stores oxygen in muscle.

Porphyrin ring

O2 bound to Fe2+

Myoglobin protein

Blackman Figure 13.37

Lecture 22-20

Chlorophyll

n  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 S

ilberberg, “Chem

istry”, McG

raw H

ill, 2006.

Lecture 22-21

Dorothy Crowfoot Hodgkin The Nobel Prize in Chemistry 1964

Nobelprize.org

Vitamin B12

Image download from Wikipedia

Lecture 22-22

CO2(g) + 2H2O(l) H3O+(aq) + HCO3

- (aq)

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). 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

Lecture 22-23

Summary

n  Concepts: q  Complex formation q  Stability constant and stepwise stability constant q  Acidity of some metal ions in solution q  Coordination compounds and geometry q  Nomenclature of coordination compounds q  Isomerism in Complexes

n  Calculations q  Complex Formation q  Equilibria in solution: complex formation + solubility

Lecture 22-24

Question

n  Does the square planar complex ion [Pt(NH3)(N3)BrCl]- have optical isomers?

Br Pt

N=N=N

N H 3

Cl

Br

Pt

N H 3

Cl N=N=N

This complex has no optical isomers because it can be superimposed

on its mirror image.