Chem. 1B – 11/15 Lecture - PowerPoint Presentation

Slide1

Chem. 1B – 11/15 Lecture

Slide2

Announcements

Today’s Lecture

Transition

Elements (Ch.

24)

Coordination Complexes

Ligand types (last time)

Geometries

Naming

Isomers

Bonding in Coordination Complexes - Theory

Slide3

Chapter 24 Transition Metals

Coordination Complex

Covered previously (to some degree as complex ions) in Chapter

16, but focus now is on molecular scale view

Coordination complexes consist of:

metal ion (typically same charge as will exist in water although stability of different oxidation states – such as Fe

2+

vs. Fe

3+

can change)

ligand(s)

counter ions (not part of complex, but associated with complex ion

)

Slide4

Chapter 24 Transition Metals

Coordination Complex – cont.

Both the metal (covered more later in the chapter) and ligand affect the type of coordination complex formed

Types of ligands:

monodentate (one metal – ligand bond per ligand)

bidentate (two metal – ligand bonds per ligand – so requires to parts of ligand capable of acting as Lewis bases)

Slide5

Chapter 24 Transition Metals

Coordination Complex – cont.

Examples: Ag(NH

3

)

2

+

= [Ag(NH

3

)2]+Ni(C2O4)2-

H3N-Ag-NH3 linear structure – uncharged monodentate ligand

oxalate is a bidentate ligand and forms a “square planar” complex (view from above)

Slide6

Chapter 24 Transition Metals

Coordination Complex - Geometries and numbers of ligands

Most Common Geometries:

Linear (with two ligands)

example:

H

3

N-Ag-NH

3

Square Planar (4 ligand bonds)example: [PtCl4]2-Tetrahedral (4 ligand bonds)example: [Zn(OH)4]2-

Zn

HO

OH

OH

OH

Slide7

Chapter 24 Transition Metals

Coordination Complex - Geometries and numbers of ligands

Most Common Geometries:

Octahedral (with six ligand bonds – note octahedral refers to 8 sides, even though 6 corners)

example: [Co(H

2

O)

6

]

2+

Co

H

2

O

OH

2

H

2

O

H

2

O

H

2

O

OH

2

Slide8

Chapter 24 Transition Metals

Coordination Complex - Geometries and numbers of ligands – Example Questions

Cobalt(II) forms a complex with three bidentate oxalate ligands. What is the geometry?

Mercury reacts with 4 I

-

ligands. What geometries are possible?

1 EDTA ligand forms an octahedral complex with Ni

2+

. EDTA is a _____ dentate ligand

Slide9

Chapter 24 Transition Metals

Coordination Complex - Geometries and numbers of ligands – More Questions

What is the metal oxidation state and number of ligands + ligand bonds for the following compounds:

1. Mg[HgCl

4

]

2. [Co(NH

3

)

5Cl]NO3 3. Na2[Cu(ox)2] (ox = C2O

42-)

Slide10

Chapter 24 Transition Metals

Coordination Complex – Naming Compounds

Naming ligands:

Neutral ligands are given molecule names (e.g. ethylenediamine) except for:

H

2

O = aqua

NH

3

= ammineCO = carbonylAnionic ligands are changed from anion:-ide becomes -o-ate becomes -ato-ite becomes -ito

Slide11

Chapter 24 Transition Metals

Coordination Complex – Naming Compounds

Naming ligands:

List names of ligands in alphabetical order before cation name

Prefixes used to indicate number of ligands (di-, tri-, tetra-, penta-, hexa-) or

bis

- ,

tris

- if ligand name already has

prefix or for polydentateMetal names (Depends on complex charge):Cations (metal name same as in ionic compounds)Anions (metal – or Latin root – ending in ate)

Slide12

Chapter 24 Transition Metals

Coordination Complex – Naming Compounds

Naming ligands – information for exam:

Too much to expect you to know all naming rules listed

Should know all 4

th

row elements plus d8 to d10 5

th

and 6

th row elementsFocus on main rules: ligands names plus 3 exceptions at top of guidelines, di- to hexa- prefixes, will give table of Latin roots (e.g. ferrate) if needed

Slide13

Chapter 24 Transition Metals

Coordination Complex – Naming Compounds – Examples:

[Ag(NH

3

)

2

]

+

=

[Pt(ox)2]2- =[Fe(NH3)4Br2]Cl = Tetracyanozincate = Pentaaquabromonickel(II) =

Sodium diaquatetrachlorovanadate(III) =

Slide14

Chapter 24 Transition Metals

Coordination Complex – Isomers

What are isomers?

Have same formula but are somehow different

Structural isomers

Have different connections between atoms

Examples:

- [Fe(NH

3

)5Br]Cl vs. [Fe(NH3)5Cl]Br (switch of counter ion with binding ion)- :CΞN: ligands can bind at C (

cyano) or N (isocyano) side

Slide15

Chapter 24 Transition Metals

Coordination Complex – Isomers

Stereoisomers

Due to different neighboring ligands

Examples: [Pt(Cl)

2

(Br)

2

]

2- (square planar)

Pt

Br

Cl

Cl

Br

Trans

isomer – like ligands apart

Pt

Br

Cl

Cl

Br

Cis

isomer – like ligands together

These will have slight differences in properties (

cis

has slight net dipole moment while

trans

does not)

Slide16

Chapter 24 Transition Metals

Coordination Complex – Isomers

Stereoisomers – cont.

For tetrahedral compounds, MX

2

Y

2

have only one isomer (X is same distance to other X and other Ys)

For octahedral compounds, MX

4Y2, also has cis- trans- isomers (guess which is trans)

M

Y

Y

X

X

M

X

X

X

X

Y

Y

M

X

X

X

X

Y

Y

Slide17

Chapter 24 Transition Metals

Coordination Complex – Isomers

Stereoisomers – cont.

For octahedral compounds, MX

3

Y

3

, also has fac- (for face) and mer- isomers (for meridinal)

M

Y

X

X

X

Y

Y

M

X

X

Y

X

Y

Y

fac

mer

Slide18

Chapter 24 Transition Metals

Coordination Complex – Isomers

Stereoisomers – cont.

The stereoisomers mentioned so are geometric isomers that will have different properties (even if only slight differences)

Another class is optical isomers, which have (mostly) identical properties; except that each isomer will rotate light differently (and can interact differently with other “chiral” molecules)

A test for an optical isomer is if its mirror image is non-superimposeable (unique)

Slide19

Chapter 24 Transition Metals

Coordination Complex – Isomers

Optical Isomers (examples)

MX

2

Y

2

– two or one optical isomer?

MABCD – two or one optical isomer?

M

Y

Y

X

X

mirror

M

B

C

A

D

120 rotation about Z axis gives back original structure

M

B

C

A

D

mirror

M

Y

Y

X

X

Not the same – if we line up A-M-D, B and C are reversed

Slide20

Chapter 24 Transition Metals

Coordination Complex – Isomers

Questions

Which of the following ligands will have linkage isomers?

NH

3

b) CN

-

c) H

2O d) SCN-e) C2O42-In what way is [Cr(NH3)

5Br]Cl2 different from [Cr(NH3)5Cl]BrCl?How many different isomers are present for the square planar compound [Pt(NH3)2ClBr]?

Slide21

Chapter 24 Transition Metals

Coordination Complex – Bonding

Theory

Valence Bond Theory and Crystal Field Theory

For

covalent bonds (valence bond theory) overlap occurs between atomic orbitals from each atom (e.g. 1s in H and sp

3

hybrid orbitals in C in CH

4

)For coordination compounds, however, electrons come fully from ligands

Slide22

Chapter 24 Transition Metals

Coordination Complex – Bonding Theory – cont.

For example, in [Zn(OH)

4

]

2-

, bonding orbitals can come from empty 4sp

3

on Zn

2+ and filled 2p orbitals on O. (All electrons from O)However, for square planar and octahedral complexes, non empty d orbitals play a role (hybrid orbitals must have d character)

Slide23

Chapter 24 Transition Metals

Coordination Complex – Bonding Theory – cont.

To understand how electrons in the d shells influence bonding, we must understand the shapes of d orbitals

Two different classes of d orbitals occurs

Off axes orbitals

x

y

z

x

y

z

d

xy

– lies in xy plane

x

y

z

d

xz

d

yz

Slide24

Chapter 24 Transition Metals

Coordination Complex – Bonding Theory – cont.

Two different classes of d orbitals occurs

On axes orbitals

x

y

z

x

y

z

d

x^2 – y^2

d

z^2