chemistry 1000 lecture 25: introduction to transition
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Chemistry 1000 Lecture 25:Introduction to transition metal chemistry
Marc R. Roussel
November 5, 2018
Marc R. Roussel Transition metals November 5, 2018 1 / 21
The transition metals
The transition metals
d block of periodic table
Sc Ti V Cr Mn Fe Co Ni Cu Zn[Ar]3d14s2 [Ar]3d24s2 [Ar]3d34s2 [Ar]3d54s1 [Ar]3d54s2 [Ar]3d64s2 [Ar]3d74s2 [Ar]3d84s2 [Ar]3d104s1 [Ar]3d104s2
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd[Kr]4d15s2 [Kr]4d25s2 [Kr]4d45s1 [Kr]4d55s1 [Kr]4d55s2 [Kr]4d75s1 [Kr]4d85s1 [Kr]4d10 [Kr]4d105s1 [Kr]4d105s2
La Hf Ta W Re Os Ir Pt Au Hg[Xe]5d16s2 [Xe]4f145d26s2 [Xe]4f145d36s2 [Xe]4f145d46s2 [Xe]4f145d56s2 [Xe]4f145d66s2 [Xe]4f145d76s2 [Xe]4f145d96s1 [Xe]4f145d106s1 [Xe]4f145d106s2
Marc R. Roussel Transition metals November 5, 2018 2 / 21
The transition metals
Chemistry of the transition metals
Electronegativities range from 1.1 (La) to 2.4 (W, Au)
Many transition metal (TM) compounds are essentially covalent
TM atoms/ions typically act as Lewis acids
Rough rule: TMs form ionic compounds in lower oxidation states,covalent compounds in higher oxidation states
Marc R. Roussel Transition metals November 5, 2018 3 / 21
The transition metals
Common and less common oxidation states:
10
Ti V Cr Mn Fe Co Ni Cu Zn
+7
+6
+5
+4
+3
+2
+1
14s2
34s2
24s2
54s1
54s2
64s2
74s2
84s2
4s1
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d
[Ar]
3d1
0
4s2
[Ar]
3d
Sc
Marc R. Roussel Transition metals November 5, 2018 4 / 21
Complexes and ligands
Complexes and ligands
Coordinate bond: bond made between a metal ion and a Lewis baseThis can almost always be considered to be an ordinary polarcovalent bond. The special name only serves to emphasizethat coordinate bonds are typically easier to rearrange thanother covalent bonds.
Coordination complex: complex molecule or ion consisting of a centralmetal atom or ion acting as a Lewis acid with coordinatebonds to one or (usually) several Lewis bases
Ligand: one of the Lewis bases in a coordination complex
Marc R. Roussel Transition metals November 5, 2018 5 / 21
Complexes and ligands
Complexes and ligands (continued)
Coordination number: number of coordinate bonds formed by a metalcentreA given metal ion in a given oxidation state typically has apreferred coordination number found in most of itscompounds.
Coordination complexes do not obey the VSEPR rules.Rather, the shape is connected to the coordination number.
Coordination number 6 gives octahedral complexes.Coordination number 4 gives either tetrahedral or square planarcomplexes.
Marc R. Roussel Transition metals November 5, 2018 6 / 21
Complexes and ligands
Example: Chloro-anions
Many metal ions form complex anions with chloride ions.
Some examples:
Complex Metal oxidation state
[CdCl4]2− 2[HgCl4]2− 2[PtCl4]2− 2[PbCl3]− 2[AgCl2]− 1[CuCl3]2− 1
Marc R. Roussel Transition metals November 5, 2018 7 / 21
Complexes and ligands
Example: Ammine-cations
Many metal ions form complex cations with ammonia.
Some examples:
Complex Metal oxidation state
[Co(NH3)6]3+ 3[Co(NH3)6]2+ 2[Ni(NH3)6]2+ 2[Cd(NH3)4]2+ 2[Cu(NH3)4]2+ 2
Marc R. Roussel Transition metals November 5, 2018 8 / 21
Complexes and ligands
Square bracket notation
In the preceding examples, you may have noticed that coordinationcomplexes are shown in square brackets.
This is important since it makes the connectivity clear: The metalatom/ion and its ligands are shown in square brackets together.
Marc R. Roussel Transition metals November 5, 2018 9 / 21
Complexes and ligands
Complex salts
A complex ion is a coordination complex with a net charge.
A complex salt is a compound in which at least one of the ions is acomplex ion.
Examples with simple counterions:
Na2[CdCl4][Co(NH3)6]Cl3
Note that we list the cation first, then the anion.
The following pairs of compounds are different:
[Co(NH3)5Br]SO4 and [Co(NH3)5SO4]Br[Co(NH3)6][Cr(CN)6] and [Cr(NH3)6][Co(CN)6].
Marc R. Roussel Transition metals November 5, 2018 10 / 21
Coordination chemistry
Monodentate ligands
Monodentate: literally, having one ‘tooth’
These are ligands that coordinate only once to a metal.
Examples of monodentate ligands:F−, Cl−, Br−, I−, OH−, H2O, NH3, CO
Note that these are all Lewis bases, but not necessarily Brønstedbases.For example, Cl− is a Lewis base, but it is not a Brønsted base.How do we know that Cl− is not a Brønsted base?
Marc R. Roussel Transition metals November 5, 2018 11 / 21
Coordination chemistry
Polydentate ligands
Bidentate: coordinates twice to a metal, i.e. can donate lone pairs fromtwo different atoms
Polydentate: coordinates more than once to a metal
Denticity: number of donor atoms in a ligand through which itcoordinates
Marc R. Roussel Transition metals November 5, 2018 12 / 21
Coordination chemistry
Polydentate ligands (continued)
Structure Denticity Abbreviation
:O:
C
:O:
O
.. 2−
..
..
..
1 or 2 CO2−3
C C
:O: :O:
:O::O:
..
2−
..
2 ox2−
N2
H
C
N
H2
H2 ..
2C
..
H
2 en
N N.. ..
2 phen
2
H2
CH2
CH
C
:O:
C
C
2H
2H C O:
:O:
C O:
:O:
NCH2N
C:O
:O:
C:O ..
4−
..
..
....
..
..
..
..
..
6 EDTA4−
Marc R. Roussel Transition metals November 5, 2018 13 / 21
Coordination chemistry
Chelates
Chelate: a complex in which a bidentate or polydentate ligand forms aclosed ring with a metal atom by forming two or morecoordinate bonds
Chelating agent: a ligand that can form chelates
Examples of chelates:
Marc R. Roussel Transition metals November 5, 2018 14 / 21
Coordination chemistry
Chelate effect
Chelates tend to be much more stable than similar complexescontaining monodentate ligands (chelate effect).
Example:
Cu2+(aq) + 4NH3(aq) [Cu(NH3)4]2+(aq) K = 1.1 × 1013
Cu2+(aq) + 2en(aq) [Cu(en)2]2+(aq) K = 1.0 × 1020
These equilibrium constants are such that Cu2+ will preferentially bind enat any reasonably comparable concentrations of en and ammonia.
Marc R. Roussel Transition metals November 5, 2018 15 / 21
Coordination chemistry
Chelation makes ions unavailable in solution.
Applications:
Added to detergents to reduce water hardness (EDTA)Food additive to prevent catalysis of oxidation by metal ions
(EDTA)Chelation therapy for metal poisoning, esp. hypercalcemia,
mercury or lead poisoning(dimercaptosuccinate)
CH
C
:O:
:O:
:S
H
C
:O:
CH
:S
H
:O
..
..
..
..
..
2−
Marc R. Roussel Transition metals November 5, 2018 16 / 21
Isomerism
Isomerism
Isomers are compounds with the same chemical formula (sameatoms), but arranged differently.
Structural isomers differ in what is bonded or coordinated to what.
Stereoisomers have identical chemical bonds, but are arranged differentlyin space.
Marc R. Roussel Transition metals November 5, 2018 17 / 21
Isomerism
Linkage isomerism: an example of structural isomerism
Linkage isomers contain a ligand coordinated to the metal centre throughdifferent donor atoms.
Example:
N3
H
N3
H
N3
H
NH3
NH3
Co
N
O O2+
yellow-orange
andN
3H
N3
H
N3
HH N3
H N3
Co
O
N O 2+
red-orange
Marc R. Roussel Transition metals November 5, 2018 18 / 21
Isomerism
Some types of stereoisomerism
Geometrical isomers have identical bonds, but the distances between somenonbonded atoms are different due to a differentarrangement of the bonds in space.
In square planar complexes with chemical formula MX2Y2 or inoctahedral complexes with formula MX2Y4, the two X ligands can beadjacent (cis) or opposed (trans).
Example:
NH3
NH3
Pt
Cl
Cl and
NH3
NH3
PtCl Cl
cis trans(cisplatin) (transplatin)
Marc R. Roussel Transition metals November 5, 2018 19 / 21
Isomerism
Example:NH3
NH3
H3N Cl
H3N
CoCl
+
cis
and
NH3
NH3
H3N Cl
NH3
Co
Cl
+
trans
Marc R. Roussel Transition metals November 5, 2018 20 / 21
Isomerism
In octahedral complexes with formula MX3Y3, the three X ligands canbe in the same face of the octahedron (fac) or along a meridian (mer):
Example:NH3
NH3
Co
NO2
O2N
NO2
H3N
fac
and
NH3
NH3
NH3
Co
NO2
O2N
O2N
mer
Marc R. Roussel Transition metals November 5, 2018 21 / 21
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