TMs 2 - Ch 8-11 - TM stability, e-counting, aqueous solns

state the 18 e- rule, its implications for reactivity, and its exceptions

d e- + ligand e^- + charge = 18 e^-

if 18 e^- = stable

< 18 e^- = reduced (+ e^-)

> 18 e^- = oxidised (- e^-)

square planar = 16 e^- (d$_{x²-y²}$ destabilised, - 2e^-

L-type ligand

2 e^- donor

“neutral”

dative bond formed

X-type ligand

1 e- donor

radical

covalent bond

Z-type ligand

0 e- donor

lewis acid - accepts 2 e- from metal

dative bond

list 5 factors that affect the strength of M-M bonding

1. spatial overlap: lower down + to left of periodic table = most diffuse orbitals so best spatial overlap

2. oxidation state: affects how e- dense metal is + how contracted

3. bond order of M-M bond: $\uparrow$ BO = $\downarrow$ bond length

4. ligand size

5. ligand number

6. bridging ligands present?

Describe the bonding in the $\eta^1$ allyl ligand

X-type

Describe the bonding in the $\eta^3$allyl ligand

LX

what is a $\mu_n$ ligand?

bridging ligand

n = no. of M centres coordinated to

what is a $\eta^n$ ligand?

$\eta$ = hapticity, no. of atoms that coordinate to metal.

e.g. Cp = $\eta^5$

polyalkenes may have multiple hapticities available.

what does $\kappa$ notation mean?

signals that the atom after it is the ligating one

e.g. dimethylphosphane-$\kappa$P = P ligates

electrons counting table

How does the strength of M-L bonding vary with oxidation state?

$\uparrow$ ox = stronger bonding

polarise ligand e- density more strongly

why don’t TMs past Mn access their maximum oxidation state?

Z_eff $\uparrow$ across period

I.E. $\uparrow$

stability $\downarrow$

How does oxidising power change across a period?

best ox power = $\downarrow$ stability as we go left to right

How is the redox potential usually defined?

Relative to SHE, for reduction of metal

+ve = reduction favourable (gain e-)

-ve = oxidation favourable (lose e-)

$$\Delta G = -nFE$$

Bronsted acidity

how easily a species DONATES PROTON

Trend in Bronsted acidity

1. across period

2. for increasing oxidation state

Both increase acidity

explanation:

HSAB - charge density

contracted orbitals

electroneutrality

how can bridging and aggregate formation be encouraged?

$\uparrow$ pH = bridging

.e.g. @ pH7, bridging may be likely to occur

as acidic metals can easily lose protons + form bridging species e.g. OH^-, O^2-

Give some examples of aggregate structures

How is a bridging O ligand generated from a hexaquo ion?

Deprotonate water (which is more acidic after coordinating to ion)

Attack another metal centre

Deprotonate + cluster as needed

$$\beta_n$$

overall thermo stability constant

= k₁k₂k₃ etc…

Irving-Williams series

rate of exchange of H₂O to L

Z_eff $\uparrow$ = more contracted = stronger binding to L = $\uparrow \beta_n$ = easier to replace H₂O

Chelate effect

1. ENTROPY favours 1x bidentate over 2x monodentate

release 2x small molecules :))

$$\Delta G = -RT \ln(\beta)$$

2. effective conc. higher once half the bidentate ligand has bound - drive reaction to complete chelation

bridging vs terminal CO stretch

bridging (3) ~ 1600-1700

bridging (2) ~ 1750-1850

terminal ~ 2000

Name 4 reaction types that metal-CO complexes can carry out

1. oxidation

2. reduction

3. substitution

4. Cluster formation (M-M bonds formed to stabilise)

How does the pi-acceptor ability of NO+ compare to CO?

NO+ = better pi acceptor, lower LUMO (+ charge)

how can TM complexes react with [NO+][BF₄^-]?

BF4- is non nucleophilic as F are very strong EWG

Tm complex reacts w/ NO+ to form NO ligand to metal

What can happen to a coordinated NO₂?

reduced to NO ligand using H⁺