Topic 10: Ligand Exchange and Stability in d-Block Complexes Flashcards
Most d-block metals react with acids to …
The metal is … which is …
liberate H2 and form a metal salt
oxidised
favourable
delta G (J) =
-nFE
n = moles of electrons transferred per mole of reaction
F = 96485 C mol^-1 (Faradays Constant)
E = Energy (V)
-(RT)lnK
Requirements for a thermodynamically favourable reaction
For the overall reaction
E > 0
G < 0
Strongly polarising, metal-aqua cations readily … to form …
As the metals charge increases, … so … may be lost to produce a …
lose a proton
an acidic solution and a Metal-Hydroxide species
It becomes even more polarising
2 protons may be lost
Oxide ligand
hydroxide and oxo ligands can lead to …which have higher …
hydroxy and oxo bridged species
nuclearity
Solvated metal cations will react with … to replace the … but sometimes …
other donor ligands
co-ordinated water ligands
not all water ligands are displaced
… charged ligands are required around a central metal ion than neutral ligands.
fewer
1st row transition metals coordinated to chloride or iodide ions tend to be … due to …
tetrahedral
packing (space around metal)
K1 (equilibrium constant) =
K2 =
K3 =
[M(L)(H2O)5]^n+/[M(H2O)6]^n+[L]
[M(L)2(H2O)4]^n+/[M(L)(H2O)5]^n+[L]
etc
beta 6 =
beta 2 =
K1 x K2 x K3 x K4 x K5 x K6
K1 x K2
log beta 6 =
logK1 + logK2 + logK3 + logK4 + logK5 + logK6
Trend in Km is … but can deviate due to …
K1 > K2 … >K6
changes in geometry or Jahn-Teller effects
Why does the value of K1 to K6 steadily decrease for ammonia complexes
The ammonia ligand can replace another ammonia ligand instead of a. H2O (fewer water molecules to replace)
To exchange a ligand, an octahedral complex must go via a … so the …
5 or 7 coordinate intermediate
CFSE is very small
Why are d^6 low complexes kinetically inert to ligand exchange?
It has a very large CFSE in the octahedral so there is a large CFAE energy barrier to ligand exchange
Why can d^10 rapidly exchange ligands
There’s a very small CFAE barrier to exchange ligands so it can rapidly exchange ligands
Do monodentate or bidentate ligands bind more strongly?
Why?
bidentate
If the bond attaching the monodentate ligand is broken, it will likely be swept away
If one bond attaching the bidentate ligand is broken, the other bond holds it near the metal so will likely re coordinate so both bonds must be broken at the same time
Entropy -
Monodentate: number of species remains same so little effect
Bidenate: increases number of species so favours chelate effect
Enthalpy:
Monodenate: lone pairs repel
bidenate: this repulsion already built in
Perfect chelate ring
The larger the ring, …
5-membered ring
the less stable as held not as close to metal ion
What do E values tell you about the likelihood of oxidation or reduction?
The more positive, the more likely reduction is (oxidation less likely)
The more negative, the less likely reduction is (oxidation more likely)
Low positive = both fairly stable
