chem1612 - pharmacy week 8: complexes ii -...
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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
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.