Coordination Chem

Question 1

How do you classify ligands?

Answer 1

1. State if acylic or cyclic
2. Number and type of donor atoms
3. Saturated or unsaturated

Question 2

What are the types fo bidentate ligands?

Answer 2

1,1 when both donor groups bonded to same C

1,2 when one bonded to carbon and other bonded to adjacent C

etc

Question 3

What are the types of isomerism in TM complexes?

Answer 3

Structural - same atoms, different order in complex

Stereoisomers - different arrangement in 3D space

Question 4

What are the forms of structural isomerism?

Answer 4

Hydration - ligand replaced by water of hydration

Ionisation isomerism - interchange of anionic ligands

Linkage isomerism - when ligand has >1 lewis base (i.e. -NO₂)

Question 5

What are the monodentate geometric isomerism in square planar & octahedral geometries?

Answer 5

Question 6

What are the octahedral geometric isomerism when there are tridentate ligands?

Answer 6

Question 7

What type of ligands prefers fac or mer isomers?

Answer 7

Fac - ligands not flat (e.g. bound to cyclohexane ligand)

Mer - requires flat (e.g. aromatic)

Question 8

What is the requirement for a chiral complex?

Answer 8

No Sn axis

Test as S1 = σ and S2 = i

Question 9

What is the equilibrium association constant (Ka) for complex formation?

Answer 9

Ka = Kon/Koff

A + B ⇔ AB

Where kon is forward reaction and koff is backwards

Question 10

What is the stability of complexes in terms of kinetics and thermodynamics?

Answer 10

Thermo - free energy changes when reversible, described by stable/unstable

Kinetic - rate of exchange proccess, descirbed by inert/labile

Question 11

How do you determine Ka?

Answer 11

UV-vis spec

Electrochemical methods

NMR

Question 12

What is the stepwise stability constant?

Answer 12

β_n = K₁ * K₂ * K₃*…K_n

βn = [ML_n] / ([M][L]ⁿ]

Different units to Kn

Question 13

What is the trend in Ka for successive binding?

Answer 13

Usually a general decrease as:

Stat less likely

Steric hindrance increasing (if larger than former ligand)

Coulombic factors if ligand more charged than former so more repulsion

Question 14

What occurs ot the Ka of Cu?

Answer 14

Decreases to n = 4 generally and then sig decreases to n=5/6

Cu2+ is d=9 so JT distortion so compresses in xy plane and elongates in z-axis

Stronger bonds to ligand in xy plane (1st 4 ligands bind here)

Question 15

What are some common deviations from standard stepwise stability constant?

Answer 15

Stereochemical change - i.e. changing from octahedral to tetrahedral

Spin state change - high to low requires large increase in Δ by overcoming pairing e-

Question 16

What is the Irving-Williams series?

Answer 16

Log K (y-axis) vs M²⁺ complex (x-axis)

Of first row TM and can be with different ligands

Question 17

What are the explanations of the trends in the Irving-Williams series?

COMMON Q

Answer 17

General increase: Zeff increases across series - r+ decreases, lowers 3d of TM so better energy match

Unusual increase after Mn: LFSE - increases from 0 at Mn²⁺ as e- fill the t2g to Ni²⁺ then decrease. Increases stability of complex

Cu2+ is high (when n=1-4) as JT effect - strong binding of ligand in xy plane

Question 18

How does LFSE change across M²⁺ across from V²⁺ to Zn²⁺?

Answer 18

Decreases from V²⁺ to 0 at Mn²⁺

Increases from Mn²⁺ to Ni²⁺

Decreases to Cu²⁺ but still higher K due to JT effect

No LFSE for Zn²⁺

Question 19

How does the irving-williams series change for K1 to K3 dissociation constants?

Answer 19

K2 is same as K1 but all values are lower

K3 is lower in general, exception is dip at Cu²⁺ (instead of peak)

Question 20

Why is there a lower than expected K3 value for octahedral Cu²⁺ compounds?

(when en complex)

Answer 20

Ligand too rigid for JT distortion, so the compound must lose the JT distortion

Question 21

What is Hard soft acid base theory?

Answer 21

Hard metal ions pair with hard ligands

Soft metal ions pair with soft ligands

Question 22

What are examples of hard metal ions?

Answer 22

Mn²⁺, Sc³⁺, Cr³⁺, Fe³⁺, Ti³⁺

Group 1 & 2, Ln³⁺

Question 23

What are examples of hard ligands?

Answer 23

F^-, R₂O, ROH, OH^-, NR₃, Cl^-

Question 24

What are examples of soft metal ions?

Answer 24

Hg⁺, Hg²⁺, Cu⁺, Ag⁺, Au⁺, Pd²⁺

Generally 2nd or lower row TM

Question 25

What are examples of soft ligands?

Answer 25

R₂S, R₃P, CO, CN^-

Question 26

What are hard-hard interactions defined by?

Answer 26

Ionic character Large HOMO-LUMO gap Dominated by desolvation of acid/base - ΔS

Question 27

How are soft-soft interactions defined?

Answer 27

Covalent character Small HOMO-LUMO gap Dominated by orbital overlap - ΔH

Question 28

How does geometric complementarity effect binding affinity?

Answer 28

Improved size match gives larger binding affinity In cryptands - larger the group favours larger cations, as determined by hard interactions so depends on release of solvation molecules from aqua-complex (ΔS favourable)

Question 29

What is the definintion of the chelate effect?

Answer 29

Enhanced stability of complexes containing chelate rings, as compared to stability of a system with fewer chelate rings

Question 30

Why does the chealate effect occur?

Answer 30

Entropically favourable - more molecules in products than reactants Enthalpically favourable - polar donor groups covalently linked to as some lp-lp repulsion in ligand synthesis, and alkyl linking donor atoms tends to increase basicity due to inductive effect

Question 31

Why does the binding of one of donor atoms bind to a ligand?

Answer 31

After first has bonded, the second is tethered to the first so effective concentration much higher than when free in solution This changes the equilibrium

Question 32

How does the chealate effect change as ring size increases and why?

Answer 32

Decreases generally Repulsion between donor atoms overcome in ligand synthesis becomes less significant as not as close Effective concentration lower as the chain increases

Question 33

What is the special case of 5/6 membered chelate rings with N donors?

Answer 33

Small ions prefer 6-membered as donor atoms closer together due to cycohexane chair Large ions prefer 5-membered as donor atoms further apart

Question 34

What is the definition of macrocyclic ligands and their properties?

Answer 34

Polydentate ligand with at least 3 donor atoms, with a cyclic structure Thermo stable - high binding constant Kinetically inert - rate of removal of M is slow

Question 35

What is the macrocyclic effect?

Answer 35

Macrocylclic ligand more stable than acyclic analogues Have to look at data to determine if enthalpically or entropically driven

Question 36

What is the effect for enthalpic preference of macrocylic?

Answer 36

Complentarity - size match leads to better M-L bonds Solvation of ligand - macrocylic ligands less strongly solvated as less exposed to solvent, less ligand-solvent bonds to break Ligand pre-organisation - synthesis overcomes repulsive forces between polar donor groups

Question 37

What is the cause of entropic effect of macrocyclic effect?

Answer 37

Conformational entropy - the more organised the more favourable ΔS, less conformatioally flexible so lose fewer degrees of freedom upon complexation

Question 38

What is the kinetic contribution to macrocyclic effect?

Answer 38

kf is formation, kd is dissociation, K = [MLⁿ⁺]/[Mⁿ⁺][L] K doesn't say anything other than absolute values of kf and kd kf / kd is sig larger for cyclic

Question 39

How does kf and kd compare in cyclic and acylic?

Answer 39

kf - cyclic 10²-10³ slower than acyclic, could be any step from: Formation of outer-sphere complex, exchange ooen solvent for a new M-L bond, repeat to form new M-L bonds kd - cyclic 10⁵-10⁷ times slower than acylclic

Question 40

What is the effect of preorganisation on stability?

Answer 40

More organised for binding & low solvation before ocmpelxation means a more stable complex

Question 41

What is the preorganisation of different macrocylic complexs?

Answer 41

From most organised & stable to least: spherand \> cryptand \> crown ether \> acyclic polyether

Question 42

What is the template effect?

Answer 42

Metal ions promote cyclisation reactions which are otherwise not possible M-L interactions used to preorganise compnents into desired geometry for reaction Favoured when conformation of reaction not thermo or kinetically favoured

Question 43

What are some examples of macrocylic synthesis?

Answer 43

Curtis synthesis of Schiff base macrocycle Schiff-Base condensation - depending on size of M can have 1+1 of separate starting materials or 2+2 S3 macrocycle - fac NC-Me (weakly coordinating) replaced with 3 S contianing ligand

Question 44

What is the thermodynamic and kinetic template effect?

Answer 44

Thermo - metal ion complexation stabilises one compnent of eqm and shifts it Kinetic - coordination of macrocylic precursor holds reactive group in correct geometry, preventing polymerisation

Question 45

What is the de-metallation problem and solution with the template effect?

Answer 45

Can be difficult to remove the metal template Solutions: add competing ligand (high conc), reduce/protonate donor groups so less affinity to metal, redox of metal

Question 46

What is the identity problem and solution with the template effect?

Answer 46

Hard to identify correct Mⁿ⁺ for a process Solutions: trial/error, metal exchange reactions, other synthetic routes like high dilution synthesis

Question 47

What is the high dilution synthesis method?

Answer 47

Synthesis of macrocycles - lower polymerisation via intermolecular reactions by working at low conc, makes intramolecular more likely

Question 48

What are the two common mechanically locked molecules?

Answer 48

Rotaxane - ring surrounding an axle with stoppers to prevent dethreading Catenane - formed of interlinked rings held mechanically Both require metal templation for any decent yield

Question 49

What metals are used in template synthesis of catenanes and rotaxanes?

Answer 49

Metal depends on coordination needed Td - Cu(I) Square planar D4h - Pd(II), Pt(II) Oh - first row TMs Linear - Ag(I), Au(I)

Question 50

Define a molecular machine

Answer 50

Molecules which carry out some type of controlled mechanical motion/work in response to external stimuli