ian Flashcards
1
Q
What is Crystal Field Theory (CFT)?
A
A model where ligands are treated as point charges that split metal d-orbitals into different energy levels
2
Q
What is Molecular Orbital Theory in complexes?
A
A covalent bonding model where metal and ligand orbitals combine to form molecular orbitals.
3
Q
Why is MO theory more accurate than CFT
A
MO theory accounts for covalency and explains why ligands influence colour, stability, and reactivity better.
4
Q
Metal - ligand bonds are
A
COVALENT BONDS in which the ligand (a LEWIS BASE) donates both
electrons to a metal centre (a LEWIS ACID)
5
Q
M-L bonds can also be called
A
CO-ORDINATION BOND
6
Q
For bonding to occur in a transition metal complex the following criteria must be met
A
Orbitals on metal (M) and ligand(s) (L) must have comparable energy.
Orbitals must have identical symmetry.
Some electrons must be available (a ligand must be able to donate electrons to the metal
7
Q
To satisfy these requirements we use metal VALANCE orbitals. Thus we use the following sets of
orbitals
A
1st row metal : 3d, 4s, 4p + ligand orbitals (lone pairs (σ) + π-orbitals)
2nd row metal : 4d, 5s, 5p + “
3rd row metal : 5d, 6s, 6p + “
8
Q
Under octahedral symmetry (Oh) we can treat what sepaately
A
σ-BONDING and π–Bonding
(not easy to do
under other symmetries/geometries).
9
Q
METAL VALENCE ORBITALS
A
3d (5 of
them), 4s and 4 p (3 of them) - 9 METAL
valance orbitals in total.
10
Q
the 4s, 4p and 3d orbitals are transfomed to octahedral symmetry into
A
4p : t1u : highest in energy
4s : a1g
3d : eg : lowest in energy
11
Q
what orbitals arent used in sigma bonding in Oh
A
dxy, dyz, dzx
these point between axis
theyre in the t2g symmetry
12
Q
describe the mo of a sigma bonding Oh complex
A
M in the middle
lines to reach the ligands which are on the axis
theres lone pairs on the ligands
13
Q
LIGAND GROUP ORBITALS in sigma bonding Oh complex
A
These are orbitals constructed from ligand orbitals (lone pairs) which
have the same symmetry as the above 6 metal valance orbitals (4s, 4px,y,z and 3dx2-y2, z2).
that we have 6 ligand -orbitals and can hence generate 6 group orbitals. We also have 6
metal valance orbitals of sigma symmetry. The remaining 3 metal valance orbitals are NON-BONDING in
the - MO diagram. Thus our complete - MO diagram should contain 15 orbitals
14
Q
What are group orbitals in this context?
A
Combinations of ligand orbitals with matching symmetry that overlap with metal orbitals.
15
Q
Which orbitals are non-bonding in a σ-only MO diagram?
A
The t2g orbitals (dxy, dxz, dyz) are non-bonding.
16
Q
Hence,* TOTAL ORBITALS in sigma-only MO (Oh) diagram:
A
2 a1g + 6 t1u + 4 eg + 3 t2g = 15 orbitals: = 6 sigma-bonding + 6 sigma -anti-bonding + 3 non-bonding
17
Q
when can we use a CFT diagram
A
when we have ligands with no pi orbital ligands or weak pi donors
18
Q
in sigma bonding in Oh, if delta o ,, how does this efect the CFT splitting levels energy
A
if delta o is small,, the eg* and t2g are weakly anti bonding or weakly non bonding respectively.
19
Q
What is π-donation and π-backbonding?
A
π-donors donate electrons into metal orbitals; π-acceptors receive electron density from the metal.
20
Q
can u have a pi bond without a sigma bond
A
nopeeeee
21
Q
what does pi bonding do to sigma bonding MO
A
it alters the sigma bonding MO diagram
22
Q
in pi bonding diagrams,, what orbital is the main ligand orbitals we use
A
we use the p orbitals on the ligands
23
Q
how many 2 p orbitals are seen in a ligand group
A
u have 12 ligand pi orbitals
group orbitals on t1u, t1g, t2u, t2g symmetry
24
Q
in pi bonding are there any metal orbitals of t1g or t2u symmetry
A
there are no metal orbitals of t1g or t2u symmetry,, these are therefore non bonding
25
t1u in pi bonding in complexes
it interacts weakly
26
pi- t2g obrital in pi bonding in complexes
theres 3 obritals
it interacts with the t2g set of metal obitals,, dyz, dxz, dyz
27
pi ligand group orbitals
dxy , dzy, dzx
28
when pi orbitals are occupied in ligands
they are pi bases aka pi electron donors
eg : Cl-
29
when pi orbitals of ligands are empty
pi acids ,, they are pi electron acceptors
CN-
30
the e.g level on CFT is dictated by what
the sigma only diagram
31
the t2g orbitals are determined by what
the pi bonding diagram
32
can we have pi bonds without sigma bonds
nope
33
can u have sigma bonds without pi bonds
yes
34
when we have a pi bonding MO diagram with the diff energy levels of orbitals,, what do we need to look at the sigma bonding version for
we need to look at what energy the eg orbital was given
35
How does π-bonding affect Δo?
π-donors (Cl-) decrease Δo - METAL t2g > LIGAND t2g
π-acceptors (CN-) increase Δo.
METAL t2g < Ligand t2g
36
delta o in pi MO diagrams is what
between the t2g and eg*
t2g is non bonding
eg8 is antibonding
37
the ligand t2g when u have pi donors iss
occupied : Cl-
the pi is occupied
38
the ligand t2g when u have a pi acceptor
CN-
the pi* is empty
39
pi acceptor ligands example
CN-
pyridine
40
pi donator ligand examples
Cl-
SO4 ^2-
41
when is the ML bond weaker in pi bonding
if the d orbital is occupied
bc the e- in the d orbital (t2g) and the electrons in the p orbital of the ligand will repel
this weakens the ML bond and gives u a smaller delta value.
example is: [RuCl6]^3/4-
bc u get pi donation to the d orbital
42
when is the ML bond stronger in pi bonding
when the d orbital of the metal is empty
bc u get pi donation from ligands like Cl- and O2-
into the empty t2g d orbitals
and there is no repulsion bc the d orbital is empty
but the p obital on the O2- or Cl- has e- in it bc theyre pi donors
43
when the ligand is a pi acceptor,, when is the ML bond strongest
when u have a CN- ligand which the metal can backbond its electrons from the t2g orbital into the pi* orbital of the ligand. pi* of CN- which is empty!!
44
what compounds is pi bonding important
in Td complexes
where the ligand is MnO4 or OsO4
45
pi bonding with pi donors
t2g of metal > t2g of ligand
decrease delta o
46
pi bonding with pi acceptors
L t2g > M t2g
increase delta o
47
What increases Δo (d-orbital splitting)
High metal charge, strong field ligands, π-acceptors, 2nd/3rd row metals.
48
What is the spectrochemical series?
A ranking of ligands from weak to strong field based on their effect on Δo.
49
Why do 4d and 5d metals have larger Δo?
Their orbitals overlap better with ligands due to their size.
50
what affects delta o
- position of metal on the periodic table
- sigma bonding
- pi bonding
- electrostatic // crystal // field
51
the chemistry of transition elements is controlled by what
the d orbital valence electron count and therefore delta o values
52
what is the electrostatic field
its generated by the L and M
its the crystal field
53
dela o is proportional to the charge on what
its proportional to the charge on the metal
due to the increased coulombic attraction upon increasing metal charge.
54
electrostatics and the radius of the metal and ligand size relationship
small ligand and smaller radius = shorter ML bond
- shorter ML bond = larger deltao value.
55
steric hinderance of ligands agsint eachother does what to the metal ligand bond
lengthens the ML bond
lowers the electrostatics and other bonding contributions
56
the larger the metal charge
the shorter the ML bond
the stronger the electrostatics
the larger the deltao
57
how does sigma bonding dtermine the magnitude of deltao
- the stronger the sigma donor (sigma base) the larger the deltao
this determines the eg sigma level on the diagram.
58
Explain the following observations – the addition of NH3(aq.) to Ni2+(aq.) produces a purple solution of [Ni(NH3)6]Cl2 whilst
NEt3 produces a pale green ppt of [Ni(OH)2]n.
NH3 (pKa of NH4+ = 9.2) is 25 x weaker as a base than Et3N (pKa of Et3NH+ = 10.6), but NH3 is the better -donor on STERIC
grounds - Et3N is too bulky to interact strongly with M
59
complexes are a balance of what
theyre a balance of the bonding interactions,, electrostaticsm,, and steric forces within a complex
60
how else does sigma bonding determine the magnitude of delta o
u can have chelating ligands which means they can bond with the metal at 2 different donor atoms. aka they can bond to the metal twice
theyre sterically more efficinet then their unidentate versions
sterically more efficient = shorter ML bond = larger delta o value.
61
how does pi bonding effect the magnitude of delta o
pi bonding determines the degree of covalency in the complex
it measures the extent of e- being shared between ML bonds. we want the e- to be smudged out around the whole complex - signifying a high degree of covalency.
62
what does pi bonding determine
pi bonding determines the energy level of t2g (pi) level
63
covalency we get from pi bondign is indicated by what
its indicated by the racah B interelectron repulsion parameter
64
a low racah B value means what
less interelectron repulsion
65
what summarises the effects of pi and sigma bonding
the spectrochemical series
66
what does the spectrochemical series rank ligands according to
it ranks ligands accoring to increasing delta o values for a given metal
67
tell us the spectrochem series
pi base, weak pi bases, pi acids
i
br
cl
no3
f
c2o4
h2o
ncs
nh3
bipy
phen
no2
h
pr3
cn-
co
68
how does the posiiton of the metal in the periodic tble determine the megnitude of delta o
going down the group increases delta o
ionic radius increases,, ML overlap increases
4d and 5d metals have a larger delta o than 3d metals
larger Metal = stronger ML overlap = shorter bond = larger delta o
69
what spin is rare to see in 4d and 5d metals
4d and 5d metals have larger ionic radii and therfore more ML overlap ,, meaning u have a larger delta o
so we are less likely to see high spin electron configurations for 4d and 5d metals.
70
why is a Co metal orange but an Ir metal colourless
bc Ir is lower in the group
meaning ionic radius is larger,, meaning ML orbital overlao inceases
meanign delta o increases
meaning energy between t2g and eg increases
meaning more energy is needed to promote the e-
meaning its colourless bc it absorbs energy from the uv region,, not the visible light region.
71
as u go down in a group what happens
the metal becomes more stable at a higher oxidation state
72
as u increase delta o what happens to the eg* level
it goes from being weakly antibonding to strongly antibonding
73
Use LFT to explain why [Fe(CN)6]3- is a
WEAK oxidant
u have one strongly bonding vacancy in the t2g orbital
however the complex is anionic - meaning its going to repel incoming e-
so its oxidising ability is weak due to this repulsion.
also bc u already have 5 e- ,, adding one more e- will result in just more interelectron repulsion between them all.
74
75
Use LFT to explain why [Co(CN)6]4- is a
STRONG reductant
d7 t2g6eg1, one strongly
anti-bonding e-. the complex is an anion
(negatively charged) - hence there is
electrostatic repulsion between the complex and
the leaving electron → loss of electron reduces
inter-electron repulsion →STRONG
REDUCTANT
76
What is Ligand Field Stabilisation Energy (LFSE)?
Energy gain from placing electrons in lower energy split d-orbitals.
77
How does LFSE affect enthalpies?
More LFSE makes hydration and lattice enthalpies more negative (more exothermic)
78
How do you calculate LFSE?
Multiply the number of electrons in t2g by −2/5Δo and in eg by +3/5Δo.
79
thermochemical properties of complexes,, what do we care about
hydration and lattice energies
stability // formation constants
80
delta H hydration refers to what process
taking a metal ion and adding H2O ligands to it
M2+ + H2O (l) → M2+ (aq.)
M2+ → [M(OH2)6]2+
81
how does a shorter ionic radi alter delta hydration
the shorter the ionic radii
the sronger the ML bond
the increase in deltaH hydration
82
hydration energy alters with what
with LFSE
83
without what is hydration a straight line
without LFSE,, delta hydration is a straight line
84
primary cooridnation shphere
the metal and the ligands directly bonded to it
85
secondary coordination shphere
the ligands attached to the ligands attached to the metal
86
tertiary coordination sphere
the lignads attached to te ligands attached to the ligands atatched to the metal
87
when u add water to a metal,, how many coordination spheres do u have
u have yp to like 3 coordination shpheres of wwater bc they can hydrogen bond to eachother
88
if u hydrate a metal and get a bunch of coordination spheres,, what else can they be referred to
they can be reffered to as the hydrated radius
89
enthalpy of hydration of gaseous ions changes with what
with charge AKA IT GETS MORE EXOTHERMIC!! LARGER NEGATIVE VALUE
BC THE METAL IS MORE POSITIVE AND THEREFORE ATTRACTS O- WATER TOWARDS IT.
as u increase the charge,, u get a larger energy of enthalpy
aka a H+ has a lower energy of enthalpy than Al3+
90
okay d orbitals can be split into what
they can be split up into eg and t2g
91
delta o fro mthe midway point to eg and to t2g
eg is destabilised by +3/5 deltao
t2g is stabilised by -2/5 deltao
92
if u have 1 e- and u have eg and t2g,, whats the energy of the d1 configuration
eg = + 3/5 deltao
t2g = -2/5 deltao
so the E = -2/5 deltao
e- config = t2g 1 eg 0
93
whats the Energy of a d8 configuration
-1.2
e- configuration = t2g^6 ,, eg^2
94
when u find the enrgy of t2g and eg,, what do u then do to fidn the total bit of energy
u do the t2g + eg
95
what happens to the LFSE when u have 2 diff configurations,, aka they can be high spin or low spin
u have 2 diff LFSE
aka d6
96
when pairing energy is more than deltao
high spin
where p is thats what it is
97
when pairing energy is lower than deltao
low spin
where.p is thats what it is
98
how many cm-1 are there in 1jkmol-1
83.7cm-1 = 1kjmol-1
99
eg is normally has what type of character and how does this change with deltao
eg is largely metal in character
weakly antibonding = small deltao
strongly antibonding = larger deltao
100
pairing up e- in an orbital does what to the pairing energy
it costs P,, as the electrons repel eachother
101
when is pairing energy used
when a pair of ekectrons is made
and this pair wasnt present in the free ion configuration
aka d8 free ion vs low spin , u have 3 paired and 2 unpaired so nothing changes,, so u dont add pairing energy
so the LFSE is just the values u get from the -2/5 or 3/5
the t2g + eg
102
when do u do LFSE + P
when u compare the free ion electron confi gand the high spin // low spin configurations and u see that he low /// high spin configs have more paired up electrons than the free ions config
free ion config = all d orbitals in a line
high // low spin: u have t2g and eg
103
what is delta H lat
this is the lattice energy
104
whats a metal oxide
metal + ocygen
105
first row metal oxides tend to have what
they tend to have the NaCl structure aka salt stucture
106
why is the lattice energy of MnO < VO
VO (V²⁺, d³) gains extra stability from LFSE → stronger ionic bonding → higher lattice energy
bc VO = 6/5 delta o
MnO = 0
MnO gets no extra stabilisation from LFSE
therefore it releases more energy when the ions come together to form the crystal structure bc theyre more stable together,, due to the added stability.
107
what is lattice energy
energy released when ions come together to form a crystal lattice
108
what does lattice energy depend onnnn : aka if we have to ocmpare lattice energy of things,, what can we look into
metal charge
ionic radii
LFSE : aka additional stabilisation
109
How do we estimate magnetic moment (μeff)
Use μeff = √[n(n+2)] where n = number of unpaired electrons.
110
When do orbital contributions matter?
In T ground terms (d1, d2, d4 low spin, etc.)
111
What is a spin-only moment?
A magnetic moment calculated assuming only spin contributes.
112
in a free ion // atom,, magnetism in atoms arises from motion of e- in what
spin motion - s and S
angular motion, l and L
113
what contributes to the total magnetic moment
the spin motion and angular motion
114
whats the total spin of an atom // ion
unpaired electrons x 1/2
115
spin only magnetic moment is measured in what units
bohr magnetrons
116
A ground term =
singly // non degenerate ground term
d3,, e- can only be placed in the enrgy levels one way
117
what is an E ground term
E = doubly degenerate ground term
aka e- can be placed in the eg // t2g orbital 2 diff ways.
aka high spin d4,, can be in the dz2 or dx2-y2
118
what is the T ground state term
its triply degenerate aka d1
it can have 3 diff possible ways of being put in the t2g orbital,, the dxz, dxy , dzy
119
why is the spin only magnetic moment a good approx for some 1st row elements but not others
for A and E ground terms,, aka singly and doubly degen,,, theres no first order orbital contribution (non degen)
in the higher energy T terms,, they can mix : aka orbital contribution (degen orbitals)
120
for T ground states what is present
an orbital contribution is preseent in the magnetic property
this means that electrons orbit the metal nuclei
if u have an unsymmetric filling of t2g.
so spi only magentic moment is not observed
121
what are the T ground states
d1
d2
d4 ls
d5 ls
d6 hs
d7 hs
122
what is L
total orbital angular momentum ,, OAM
123
when u have a Td complex,, how can the orbital angular momentum aka L,, be quenched // reduced
by applying a ligand field
124
when is the spin only magnetic moment not useful
for T complexes,, aka triply degenerate complexes as they have orbital contribution
125
does the spin only formula work well for Td complexes
it works well for 1st row elements but shows deviation for 2nd / 3rd row systems
126
for Td complexes,, what block electrons are almost completely unquenched
quenched = weakened
unquenched means its not weakened at all.aka for f electrons,, orbital angular momentum is almost completely unquenched.
the f orbitals interact very weakly with ligand field.
127
S + L equation. spin only.
root 4S(S+1)+L(L+1)
128
Why do d8 metals differ in geometry between 1st and 2nd/3rd row?
1st row (e.g. Ni²⁺) favours tetrahedral; 2nd/3rd row (e.g. Pd²⁺) favour square planar due to larger Δo.
129
What’s the order of d-orbital energies in square planar complexes?
dx²−y² > dxy > dxz/dyz > dz²
130
in the MO of Oh,, we could separate pi and sigma bonding,, can u do this in Td complexes
no,, u cant separate the different bonding
131
whats missing in the energy level orbitals of those with Td
they have no g // u subscripts bc they dont have an inversion centre
132
what type of bonding is important in Td complexes
pi bonding is important in Td complexes
133
when we have Td complexes,, why are MOs kinda hard to do
bc e and t2 energy levels vary with pi bonding
the deltaT value is hard to predict
134
is delta T or delta O larger
deltaT is 4/9th that of deltaO,, bc there are 4 ligands instead of 6,, meaning less ligand interaction and therefore less splitting
135
in trigonal bipyramidal fields,, what d orbital points at all ligands
the dz2 orbital points at all ligands making it strongly antibonding
bc it interacts with lots of ligands,, meaning its energy is very high,, making it extremely antibonding
136
describe how d orbitals split for a trigonal bipyramidal complex
dz2
(gap is §2)
dxy , dx2-y2
(gap is §1)
dxz dyz
gap 2 is large than gap 1
137
between octahedral and square planar,, what geometry is there
tetragonal distortion
long x axis bonds
138
Why is NiCl42- tetrahedral and PdCl42- square planar? Both Ni(II) and Pd(II) are d8.
- both d8, both same ligand
- difference = orbital size
- larger diffuse orbitals = more overlap with ligands
- this makes DELTA value larger,, even if ligand is weak field.
- larger delta = pairing energy is probs lower, so it will be low spin aka SQUARE PLANAR
- if orbitals are smaller, ,theres lower overlap with ligands
- this means than DELTA is smaller,, meaning pairing energy is higher,, so its more likely to be high spin,, so tetrahedral is preferred.
- low spin = square planar
- high spin = tetrahedral
Ni2+ is only moderately charged and Cl- low in spectrochemical series → Δ values are low → (anionic) inter-
ligand repulsion and pairing energies are high → high spin d8 (TETRAHEDRAL).
* Pd2+ 2nd row element Δ values are high → eg and hence dx2-y2 are strongly anti-bonding low spin d8 =
(SQUARE PLANAR
139
what does tetragonal distortion look like
super long z bonds
140
what should we rmemeber about the energy levels when it comes to tetragonal and square planar
tetragonal : Z orbitals are lower in energy due to the Z ligands being further from the ligand ,, this minimises the orbitals with z character energy but u dont get overlap
square planar: Z orbitals are now no longer there,, soany orbitals with z character are much lower in energy as they arent interacting with ligands anymore
the orbitals with z character are now lower in energy than the xy ones. so u see overlap.
141
Cl is what type of ligand
its a pi base,, donates electrons
so the delta value will be small
its an anion to LL repulsion is larger
142
why else can the Ni2+ complex tetrahedral
bc theres 4 ligands theres either tetrahedral or square planar geometry
bc CCl- has larger LL repulsions
and Td is the most sterically efficient 4 ligand geometry!!! and bc Ni only has 3d orbitals,, its much smaller than the Pd,, and bc its small,, the steric repulsions between Cl- are large,, and bc tetrahedral is the most sterically efficient 4 ligandgeom,, we want it.
so the Ni geom is dominated by steric factors
143
why is the Pd2+ structure square planar
bc its larger due to being a second row metal.
meaning the LL repsulsion is lower,, meaning u can relax on the steric factors and wanting the ligands to be as far as possible (tetrahedral geometry)
Pd is square planar due to electronic factors,, dx2-y2 is strongly antibonding and e- dont go into it.
144
why is tetrahedral geom more sterically efficient then square planar
tetrahedral = 109.5
square planar is 90
145
why are square planar complexes always low spin
bc they have a high energy antibonding ,,, eg*
and e- dont want to go into them
146
what do we need to be careful of d8 complexes
larger delta value = low spin so maybe square planar
147
in square planar complexes,, whats the energy difference between the dx2-y2 and dxy orbital
its deltaO
aka the splitting of thr parent octahrdal complex
148
what row d8 elements are usually always square planar complexes
2nd and 3rd row metals are usually always square planar
larger orbitals = better ligand overlap = larger delta O so low spin
149
splitting in square planar complexes is equal to what
1.3 deltaO
this larger splitting makes up for the loss of 2 ligands
150
What causes the Jahn-Teller effect?
Electron degeneracy in eg orbitals causes distortion to lower energy.
151
What distortions occur in d⁹ and d¹ systems
d⁹ (e.g. Cu²⁺): elongation; d¹ (e.g. Ti³⁺): compression.
152
What are consequences of Jahn-Teller distortion?
Changes in geometry, reactivity, and spectral properties.
153
what is the jahn teller statement
for non linear molecules ]]if the ground state is orbitally degenerate the moelcule would distort to remove degeneracy.
aka if orbitals of the same eenrgu : eg vs t2g are filled with diff amounts of e-,, the moelcule will distort to remove the orbitals degeneracy
154
what type of jahn teller is seen in d9 moelcules
in d9 we see jahn teller elongation
where the degernate eg orbitals have their degeneravy removed due to uneven filling of orbitals
this is a large // strong degeneracy in orbitals that point at ligands. the Z orbital is reduced in energy but dont overlap with the t2g ones.
155
elongated jahn teller gives u what
tetragonal distortion
large distortion
the Z character orbitals are redcued in energy
z bonds are longer
vibration happens up and down these bonds
4 short bonds,, 2 long bonds
156
what jah teller distorion do we get for d1
we get compression
z bonds get shorter
orbitals with z character therefore increase in energyy
theres no overlap between eg and t2g
we get tetragonal compression
this is weak degeneracy / /small degeneracy in orbitals that point between ligands
x = y but not z
157
theres tetragonal distortion but also what other distortion do we have
rhombic
where u have small, medium and long bonds
where x doesnt equal y doesnt equal z
158
what e- configs does jahn teller occur in
d1, d2, d4, d5ls, d6hs, d7, d9
159
when are distortions in bond length when it comes to jahn teller more distinctive
when the degenerate electrons are in the eg level .
bc these orbtials point at ligands
160
what explains distortions from ideal geometries
jahn teller
161
whats a dymanic JT effect
its where the distorted axis flips from axis to axis
aka diff bonds get longer,, not just the z bonds,, the y and x ones can get longer too.
while the z remain short
162
are longer bonds stronger or weaker
theyre weaker
meaning when u have a JT distortion,, the longer bonds are more likely to undergo ligand substitution
163
what does JT resuilt in and explain plssss
it results in unsymmetrical bands in electronic spec.
Let’s talk electronic spectra a.k.a. what we see in UV-Vis:
Normally in a perfect octahedral complex, you’d get one nice, symmetrical d–d transition band
BUT with Jahn–Teller distortion, the symmetry is broken
Now the d-orbitals aren’t perfectly degenerate, and the transitions split:
Some transitions shift up or down
Some become partially allowed (due to symmetry lowering)
→ They result in broader, unsymmetrical, or split bands in the UV-Vis spectrum
bc theres more transitions that can occur between the diff energy levels of the d obritals due to their distortion,, and this causes abs at diff wavelengths!! leading to asymmetric absorption bands in uvvis. bc normally it would just be 1-2 bands from dxy // dzy dzx toooo the eg orbitals
164
What is HSAB theory?
Hard/Soft Acid-Base theory: hard acids prefer hard bases; soft acids prefer soft bases.
165
What is the chelate effect?
Multidentate ligands form more stable complexes due to entropy.
166
What is the macrocyclic effect?
Macrocycles are even more stable due to pre-organisation and reduced strain.
167
in a complex,, what is the acid and what is the base
acids accept to metal is the acid
meaning ligands are the base
168
when we say strong acid what do we mean
we mean the metal
wr want it to be small,, highly charged,, a metal cation
low polarisability
good sigma acids
H+, LI+ , Na+, K + , Be2+ , Mg2+ , Al2+ , In3+, Sc3+, Ti4+ , Cr3+ , Co3+
also the actinides and anthanides ,, high oxidation state metals
169
when we have hard bases what do we think
bases so ligands
high electronegativity
low polarisability
not easily oxidised (hard to give e- over ,, aka high electronegativity)
- no pi acceptor orbitals
amines,, ammonia ,, o- donors ,, F-
NOF ligands
170
what do we think of when we say soft acids
acids = the metal
zero charge or low charge metal atoms or cations
high polarisability
good sigma bases
Ru, Os , Rh Ir (||)
Pd, Pt || and |v , Cu Ag Au Hg Hg Ti Pb
171
what should we think when we see soft bases
bases so ligands
low electronegativity
high polarisability
easily oxidised
P, As, Sb, S, Se donors
I->Br->Cl-
alkyls, alkenes, alkynes, CO, CN, isocyanides and some metals
172
hard-soft chacater may be though interms of what
atomic or molecular polarisabiltiy
173
equation for polarisability
induced dipole moent = POLARISABILITY (J-1C2m2) X electric field
174
a values of soft donors // acceptors
high polarisabilty values
175
hard donors//acceptors have what a value
low polarisability
176
a =
polarisability
K-1C2M2
177
E =
electric field strength
178
longu =
induced dipole moment
179
what is a labile complex
exchange ligands rapidly
low LFSE
180
whats an inert complex
exchange ligands slowly
have high LFSE
181
when u have a high LFSE in a complex,, what does it prevent
it prevents it from transforming into its optical isomer. bc a large negative LFSE means its very stable and inert. meaning it cant flip from one isomer to another.
182
when u have a complex with a high LFSE but want its optical isomer form,, what can u do
we need to lower the negative LFSE to make it more labile and less inert.
we do this using graphite as it can reduce a metal ion (it gains an e-) which makes its LFSE less negative which is more labile,, allowing ligands to move and rearrange
183
what is the bailar twist mechanism
a way or rearranging ligands in a tris bidentate complex without breaking bonds in order to get its optical isomer
it occurs by going froom one form,, to forming a trigonal prism,, to forming the mirror image // optical isomer.
it reduces the energy of the eg orbital and it splits the t2g orbital. with a1 being the lower energy.
184
whats the dissociative mechanism in complexes
where a ligand can leave the complex and create a vacancy a diff ligand can then take.
the rate of dissociation occurs based on the identity of the leaving ligand
185
what does : metal ions are solvated in solution mean
it means that when u put a metal in a soluitoon,, the thing the solution is made up of will coordinate to the metal using its lone pair
this means that complex formation reactions are ligands susbtitution reactions!! bc the metal has ligands on it already ,, aka the ones from solution
186
whats the Kf of complexes
[products] / [ reactants]
u put their charge on the top right of the conc
187
what does it mean when Kf > 1
the ligand is bound stronger to the mrtal than water
188
when the Kf < 1 what does it mean
that the ligand is bound more weakly than H2O.
189
formations constants are diff to what
theyre different to rate constants
190
the conc of water when forming complexes in water is said to be what
its said to remain constant!!!
around 55.5M
191
what happens when we do k1 x k2
we can cross cancel things out to get the k for the product of both k's
and this gives us the overall formation constant for the k's multiplied together
if u have 2 things that u multiply u add the power!!! aka if u have [L] x [L] you would get [L]2 as the product
192
whats bigger k1 k2 k3 k4
k1
but it also assumes that metal ligand bond energies dont change very much along the series.
193
in the K equations of complexes,, how can we change the position of the equilibrium
we change via le chatliers prnciple
194
What is the formation constant expression for the complex
[Fe(bipy)3]2+ in aqueous solution?
Write out the formation reaction and then write the equilibrium constant
expression for that reaction. The reaction is
Fe2+(aq) + 3 bipy (aq) → [Fe(bipy)3]2+
then product conc // reactant and make sur eu put to the power of 3 for bipy.
195
What is the formation constant expression for the complex Co(NH3)5NO22+ in aqueous solution?
Co3+(aq) + 5NH3(aq) + NO2-(aq) → [Co(NH3)5NO2]2+ (aq.)
196
In general K1 > K2 > K3 … > Kn values steadily decrease because of
- STATISTICS - less H2O ligands to displace, more L groups to displace. Incoming ligand can displace H2O or
L more likely H2O at the beginning of the reaction sequence than at the end
- 2) STERICS - in cases where bulky ligand displace less bulky ligands.
- CHARGE - charged ligands become increasingly more difficult to introduce on electrostatic grounds.
Increasing charge density will also tend to reduce LFSE value
197
β3 [Ni(en)3]2+ ~ 10^18 ; β6 [Ni(NH3)6]2+ ~ 10^8 – what is the K value for: [Ni(NH3)6]2+ + 3 en → [Ni(en)3]2+
pro / rea = 10^10
198
FACTORS WHICH DETERMINE STABILITY CONSTANTS: High Kn or βn values are given by
- Chelating systems.
- High LFSE.
- Hard-soft metal-ligand matched preferences.
199
recall the 2 gibbs equation
delta G = deltaH - TdeltaS
deltaG = -RT ln(k)
200
whats the chelate effect
when u get enhanced stability of a complex when u use a chelating ligand over its unidentate analogues.
201
when u go from unidentate to a chelating ligand,, u go from how many moles to how many moles
complex of 6 water ligands + 3en --> complex with 3en + 6 water ligabnds
increase in entropy!!!
making G more negative
202
sometimes theres non change in moles when ligand substitution occurs but why can entropy decrease,,
dur to changes in solvation of ions and ligands
203
the chelate effect issss
largely entropic in nature
204
whats a macrocyclic ligand
a large cyclic ligand that contains 3 or more donor atoms
205
whats the macrocyclic effect
the enhanced stability of a macrocyclic ligand over its open chain analogue
206
macrocyclic ligands have larger what values than their open chain analogues
they have a higehr Kf value .. aka formation constant
do to the chelating effect // its cyclic nature
207
where are macrocyclic ligands used in
theyre used in medicine in mri and stuff like that
208
when Kn < Kn+1 (i.e. normal trend is not observed) what could be the reason
indicates change in structure/bonding (electronics)
209
Why is K4 > K3 for Cd2+ (aq.) + n Br- [CdBr4]2
This reaction involves a structural change:
Cd2+(aq.) = [Cd(H2O)6]2+ is octahedral [CdBr4]2- is tetrahedral.
Last H2O displacement yields a tetrahedral complex - sterically less crowed than an octahedral complex
This is a
STRUCTURAL
(STERIC) change
yielding a favourable
ENTROPY term. entropy is positive and larger so enthalpy will therefore be more negative
bc ur going from 2 moles to 4 moles
210
metal (aq) means what
it means meta in Oh with water ligands around it
211
what does a larger Kf value mean
it implies that that reaction is particularly favourable compared to the other ones
could be entropically favoured
or go from high spin to low spin by enlarging delta value
212
are Kf values of ligands set in stone
nope
they vary from metal to metal
213
what is the irving williams series
Ba2+ < Sr2+ < Ca2+ < Mg2+ <
Mn2+ < Fe2+ < Co2+ < Ni2+ < Cu2+ > Zn2+
shortcut to predicting stability of metal complexes across the first-row transition metals
observed trend in stability constants for divalent metal ion complexes (M²⁺) with the same ligand, across the 3d block from Mn²⁺ to Zn²⁺.
Complexes of Mn²⁺ are the least stable (weakest binding)
Complexes of Cu²⁺ are the most stable
Zn²⁺ drops off again after Cu²⁺
The series reflects largely electrostatic effects (see
CFT notes) – smaller cations result in shorter metal
ligand distances and hence stronger bonds
For ions beyond Mn the series reflects increasing
LFSE values
Note Cu > Ni – Cu has an extra eg electron (lowers
LFSE) but J-T effect helps stabilisation – reduces steric
and electrostatic repulsions of ligands
