Complex Chemistry

Question 1

What are the most common shapes of complexes?

Answer 1

tetrahedral and octahedral

Question 2

What are complexes in terms of adducts?

Answer 2

acid-base adducts (lewis acid base theory)

Question 3

What is a Lewis acid?

Answer 3

Molecule that is an acceptor of a lone pair/electron density

Question 4

What is a Lewis base?

Answer 4

Molecule that is willing to donate an electron pair/electron density

Question 5

What do metal cations usually react as in terms of lewis acid base theory?

Answer 5

Lewis acid

Question 6

What is the coordination number?

Answer 6

number of ligands bonded to the central atom

Question 7

What are monodentate ligands?

Answer 7

Ligand has only one atom that can bind to central atom

Question 8

What are bidentate ligands?

Answer 8

Ligand has two atoms that can bind to the central atom

Question 9

What is an example of a monodentate ligand?

Answer 9

cyanate (NCO), chloride (Cl-), cyanite (CN-)

Question 10

What is another name for bidentate ligands?

Answer 10

Chelate ligands

Question 11

are mono or bidentate ligands kinetically favoured?

Answer 11

Chelate ligands/Bidentate ligands are usually kinetically favoured because they tend to coordinate better, than two monodentates

Question 12

What is an example of a bidentate ligand?

Answer 12

ethylenediamine (en), carbonate, oxolate

Question 13

What is an example of a polydentate?

Answer 13

crown ether, porphyrins (square planar structure), EDTA 4-

Question 14

Define a protonated form of a molecule?

Answer 14

Has protons that it is able to donate. Deprotonated form does not have protons

Question 15

Is the protonated or the deprotonated form of EDTA 4- soluble in water?

Answer 15

the deprotonated form.

Question 16

What is the chelate effect?

Answer 16

chelate ligands with n donor atoms of a polydentate coordinates better/stronger than n monodentates, due to the increase in entropy the reaction with a polydentate causes

Question 17

Explain why complexes are more stabilized through polydentate ligands than monodentate ligands?

Answer 17

This is due to the chelate effect that says that polydentate ligands form more stable complexes than monodentate ligands. This is due to an entropy effect:

1. ΔS is positive to the right, that drives ΔG to be spontaneous
2. if one end of a bidentate ligand detaches from metal cation, it will likely reattach itself before the other end becomes separated if the chain connecting them is short (otherwise the loose end may drift away)

Question 18

Give an example reaction that shows the chelate effect

Answer 18

[M(H2O)6]2+ + [EDTAH2]2- => (Crab) + 6 H2O + 2 H+

[Co(NH3)6]2+ + 3en -> [Co(en)3]2+ + 6NH3

Question 19

Draw the structure of protonated [EDTAH2]2-

Answer 19

Structure

Question 20

What is a stability constant?

Answer 20

Constant that determines whether the complex will be stable as a structure

Kb = products/reactants

Question 21

What happens if Kb (stability constant) is high?

Answer 21

the more stable the complex and the stronger the ligand

Question 22

Why are the most common coordination numbers of main group elements, 4 and 6?

Answer 22

Only has empty s or p orbitals. This means they only have a positive charge which can be saturated by electron density of ligands

Question 23

What do d electrons determine in coordination chemistry?

Answer 23

colour, coordination number and catalytic activity

Question 24

what does degenerate mean in terms of d-orbitals?

Answer 24

same energy level

Question 25

What happens to the d-orbitals when ligands approach?

Answer 25

Ligands will cause d-orbitals to split. Depending on the orientation (magnetic quantum nr) of the d-orbitals, the interaction between orbitals and ligand may change.

Question 26

Draw the energy splitting in an octahedral ligand field

Answer 26

double degenerate

triple degenerate

Question 27

Does a small split in d-orbitals cause a high or low spin?

Answer 27

High spin (as electrons can have an orbital on their own and spin is maximized. if double occupation occurs, the spins are cancelled out by another)

Question 28

Does a high split in d-orbitals cause a high or low spin?

Answer 28

low spin. usually 4d or 5d orbitals because they are heavier

Question 29

What do low spin complexes have? (high split)

Answer 29

reduced magnetic moment and smaller ionic radius

Question 30

What is the difference between paramagnetic and diamagnetic?

Answer 30

Diamagnetic: all spins are paired and cancel out

Question 31

If the ligand causes a low spin, is it weak or strong?

Answer 31

High split, therefore strong ligand

Question 32

What is the spectrochemical series?

Answer 32

list of ligands based on their strength of interaction with metal cation

Question 33

Order the following according to ligand strength: F-, Cl-, Br-, I-

Answer 33

I < Br < Cl

Question 34

What is an example of a strong ligand?

Answer 34

CO > CN- > NO2-> en

Question 35

What does ligand field splitting depend on?

Answer 35

• metal
• increase in oxidation number, increases splitting
• principle quantum number of d-orbital

3d (low split) < 4d < 5d (high split)

Question 36

Draw the d-orbital splitting of tetrahedral complex

Answer 36

(flip of octahedral)

Question 37

Why do tetrahedral complexes almost exclusively have HIGH spin complexes?

Answer 37

due to very small ligand splitting

Question 38

Why do octahedral complexes of 4d and 5d elements mostly have low spin configurations?

Answer 38

magnitude of splitting energy increases, with increasing quantum number.
4d/5d have high split = low spin