Transition Metal Complexes Flashcards
1
Q
Definition
the collective name for the dxy, dxz and dyz orbitals
A
T2g orbital
2
Q
Show that the following complexes obey the 18-electron rule:
(a) [Ni(CO)4]
(b) [Mn(CO)5]-
A
3
Q
Definition
The energy of the electron configuration in the ligand field minus the energy of the electronic configuration in the isotropic field
A
Crystal field stabilisation energy
4
Q
In the elements, which orbital is filled first: 3d or 4s?
A
4s
5
Q
Definition
Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs
A
High spin
6
Q
Definition
similar to the chelate effect however the effect is further enhanced by the cyclic conformation of the ligand. These ligands are not only multidentate, but because of their pre-organised structure there is little entropy penalty for wrapping it around the metal ion
A
Macrocycle effect
7
Q
Predict which of the following complexes would be most stable:
(a) [Fe(OH2)6]2+
(b) [Fe(OH2)6]3+
A
8
Q
Definition
a technique used to determine analyte concentration by measuring light absorption across the ultraviolet and visible light wavelengths
A
UV-vis spectroscopy
9
Q
What causes low-spin arrangments?
A
When Δo is large and too much energy is required to promote electrons into the eg orbital
10
Q
How are values of Δo measured experiementally?
A
UV-vis spectroscopy
11
Q
Define
Coordination number
A
the number of atoms or ions immediately surrounding a central atom in a complex or crystal
12
Q
Calculate CFSE for the low-spin and high-spin configurations of d7 . Which one looks as if it should be the most stable
A
13
Q
Definition
A rule based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs
A
Eighteen electron rule
14
Q
Using the formula Δ0 = hcNo/λ, convert the value of Δ0 = 12600 cm-1 for [Cu(OH2)6]2+ into kJ/mol
A
15
Q
Definition
the difference in energy between eg and t2g
A
ΔO
16
Q
Define
Lewis acid
A
a compound or ionic species which can accept an electron pair from a donor compound
17
Q
Define
Metal-ligand charge transfer
A
when the electronic charge shifts from the MO with metal-like character to the ligand-like one resulting in the oxidation of the metal centre
18
Q
Definition
a spectroscopic selection rule that states the a change in spin multiplicity is forbidden
A
Spin selection rule
19
Q
Define
High spin
A
Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs
20
Q
Assuming that the following complexes obey the 18-electron rule, determine n in each complex:
(a) [Fe(CO)<em>n</em>]
(b) [Fe(CO)<em>n</em>(PPh3)2]
A
21
Q
Define
Crystal field stabilisation energy
A
The energy of the electron configuration in the ligand field minus the energy of the electronic configuration in the isotropic field
22
Q
Is [Fe(CN)6]4- more stable in high spin or low spin?
A
Low spin; CN is a carbon donor and therefore the crystal field splitting is large making it more stable to have low spin
23
Q
Definition
the number of atoms or ions immediately surrounding a central atom in a complex or crystal
A
Coordination number
24
Q
Define
Low spin
A
Crystal field designation for an inner orbital complex; contains electrons paired t2g orbitals before eg orbitals are occupied in octahedral complexes
25
# Define
Lewis base
a compound or ionic species which can donate an electron pair to an acceptor compound
26
# Definition
the collective name for the dz2 and the dx2-y2 orbitals
Eg orbital
27
What is the electron configuration of chromium metal?
Cr: [Ar] 4s13d5
28
How does oxidation state effect crystal field splitting?
The higher the oxidation state of the metal, the greater the crystal field splitting
29
# Definition
a compound or ionic species which can accept an electron pair from a donor compound
Lewis acid
30
# Define
UV-vis spectroscopy
a technique used to determine analyte concentration by measuring light absorption across the ultraviolet and visible light wavelengths
31
# Definition
a spectroscopic selection rule that only applies to centrosymmetric molecules (those with an inversion centre) and atoms. It states that transitions can only occur if they result in a change in the value of the subsidiary quantum number, l. Thus, allowed transition are s -\> p, p -\> d and d -\>f.
Laporte's selection rule
32
# Define
Macrocycle effect
similar to the chelate effect however the effect is further enhanced by the cyclic conformation of the ligand. These ligands are not only multidentate, but because of their pre-organised structure there is little entropy penalty for wrapping it around the metal ion
33
Show both high-spin and low-spin filling for d4
34
Ligands up to an including _______ in the spectrochemical series usually give rise to high spin complexes
H2O
35
How does the crystal field splitting change from the second transition series compared to the first?
Increases by 50%
36
What causes high-spin arrangements?
When Δo is small
37
# Define
Barycentre
the zero-energy reference in octahedral complexes
38
# Definition
a compound or ionic species which can donate an electron pair to an acceptor compound
Lewis base
39
# Define
Laporte's selection rule
a spectroscopic selection rule that only applies to centrosymmetric molecules (those with an inversion centre) and atoms. It states that transitions can only occur if they result in a change in the value of the subsidiary quantum number, l. Thus, allowed transition are s -\> p, p -\> d and d -\>f.
40
# Define
Eg orbital
the collective name for the dz2 and the dx2-y2 orbitals
41
# Definition
a model that describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution
Crystal field theory
42
What is the general rule used to determine the value of the crystal field theory?
X- donor \< O donor \< N donor \< C donor
43
What happens when 5 degenerate d orbitals are split into two sets?
3 t2g orbitals of lower energy and 2 eg orbitals of higher energy are produced
44
# Define
Spin selection rule
a spectroscopic selection rule that states the a change in spin multiplicity is forbidden
45
# Definition
Crystal field designation for an inner orbital complex; contains electrons paired t2g orbitals before eg orbitals are occupied in octahedral complexes
Low spin
46
# Define
Chelate effect
the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal
47
What is the electron configuration of Fe3+ ?
[Ar] 3d5
48
What factors effect crystal field splitting?
1. The identity of the metal
2. The oxidation state of the metal
3. The number of the ligands
4. The nature of the ligands
49
What does the splitting of d orbitals lead to?
Overall lowering of energy and consequently the complex is more stable than before the splitting
50
# Define
ΔO
the difference in energy between eg and t2g
51
In compounds, what is an easy way to determine the number of d electrons?
The group number of the metal
52
# Define
Crystal field theory
a model that describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution
53
What is the energy separation between the t2g and the eg orbitals called?
Δoct
54
# Definition
a geometric distortion of a non-linear molecular system that reduces its symmetry and energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds
Jahn-Teller distortion
55
# Define
Eighteen electron rule
A rule based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs
56
What does the 18-electron rule state?
a complex is stable if there are 18 electrons around the metal
57
What is the electron configuration of V3+ ?
[Ar] 3d2
58
# Definition
a substance whose molecules can form several bonds to a single metal ion. i.e. multidentate
Chelating agent
59
# Definition
the zero-energy reference in octahedral complexes
Barycentre
60
# Define
Chelating agent
a substance whose molecules can form several bonds to a single metal ion. i.e. multidentate
61
# Definition
the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal
Chelate effect
62
# Define
T2g orbital
the collective name for the dxy, dxz and dyz orbitals
63
# Definition
when the electronic charge shifts from the MO with metal-like character to the ligand-like one resulting in the oxidation of the metal centre
Metal-ligand charge transfer
64
# Define
Jahn-Teller distortion
a geometric distortion of a non-linear molecular system that reduces its symmetry and energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds
65
How does the number of ligands effect crystal field splitting?
The crystal field splitting is greater for a larger number of ligands
66
Convert the value of ΔO= 12600cm-1 for[Cu(OH2)6]2+ into kJ mol-1
ΔO = E = *hv*NO = *hc*NO/λ
Where *h* = 6.63 x 10-34 (J s; Plank's constant)
*c* = 3 x 108 (m s-1; Speec of light)
NO = 6.022 x 1023 (mol-1; Avogadro's constant)
67
Which two selection rules determine whether a particular transition is allowed or forbidden?
Laporte's selection rule
Spin selection rule
68
What type of molecules does Laporte's selection rule apply to?
Molecules that have a centre of inversion
69
According to Laporte's selection rule, why are tetrahedral complexes more strongly coloured than octahedral ones?
Tetrahedral complexes do not have a centre of inversion so Laporte's rule does not apply to them like it does octahedral complexes which means that more transitions are allowed
70
What orbital transitions occur in ligand-metal charge transfer?
p -\> d
71
When can metal-ligand charge transfer occur?
When the ligand has an empty p orbital that can accept electrons from the metal
72
Why do d5 complexes only give a series of very weak absorption bands?
According to the spin selection rule, changes in spin multiplicity is forbidden. Since d5 complexes have 1 electron in each orbital no transitions are possible that wouldn't break this rule
73
(a) TiO2 is the most common white pigment, why is it white?
74
(b) Explain why [Mn(OH2)6]2+ is a very pale pink colour
75
(c) Explain why metal chromates (CrO42-) have been used as yellow pigments
76
Why are tetrahedral complexes almost always high spin?
ΔT = 4/9 ΔO
77
How does the splitting diagram for a tetrahedral complex compare to an octahedral complex? Why?
It is inverted; t2 (xy, xz, yz) orbitals are higher in energy, e (x2-y2, z2) orbitals are lower
Since tetrahedral complexes have only four ligands instead of six, the ligands don't quite point directly at the three d orbitals, causing the crystal field splitting to be much less than in the octahedral case making them less stable
78
79
What geometric formation do complexes with 8d electrons tend to form?
Square planar
80
True or False:
ΔSP \> ΔO
True
81
Show arrangement of electron in an a) octahedral, b) tetrahedral and c) square planar d8 metal ion
82
Which octahedral complexes are effected by Jahn-Teller distortion? Why?
Octahedral complexes of d9, low-spin d7 and high spin d4 due to unsymmetrically filled eg orbitals
83
True or False:
Jahn-Teller distortion decreases stability of complexes
False; the distortion increases crystal field splitting and enhances stability
84
85
What is the chelate effect caused by?
Differences in reaction entropy between chelated and nonchelated complexes in dilute solution. The chelation reaction results in an increase in the number of independent molecule in solution. By contrast, the nonchelating reaction produces no net change. The former therefore has the more positive reaction entropy and hence is the more favoured process
86
# Define
Antibonding orbital
a type of molecular orbital (MO) that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms
87
# Define
Destructive interference
the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other
88
# Define
Dissociation constant
a quantity expressing the extent to which a particular substance in solution is dissociated into ions, equal to the product of the concentrations of the respective ions divided by the concentration of the undissociated molecule
89
# Define
Electrode potential
the electromotive force of a cell built of two electrodes
90
# Define
Equilibrium constant
a number that expresses the relationship between the amounts of products and reactants present at equilibrium in a reversible chemical reaction at a given temperature
91
# Define
Formation constant
the equilibrium constant for the formation of a complex ion from its components in solution
92
# Define
Hess's law
A law that states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes
93
# Define
Hund's rule
every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin
94
# Define
Irving-Williams series
the relative stabilities of complexes formed by transition metals as represented in a diagram
95
# Define
Latimer diagram
a summary of the standard electrode potential data of that element
96
# Define
Ligand field theory
one of several theories that describe the electronic structure of coordination or complex compounds, notably transition metal complexes. It factors in the effects of π bonds as well as σ bonds
97
# Define
Oxidation
the loss of electrons during a reaction by a molecule, atom or ion
98
# Define
Pauli exclusion principle
in an atom or molecule, no two electrons can have the same four electronic quantum numbers
99
# Define
π-acids
a ligand that accepts electron density into it's p orbital from the metal center
100
# Define
π-bases
a ligand with filled π-type orbitals that donates electron density to the metal center
101
# Define
π bond
a covalent bond formed between two neighboring atom's unbonded p-orbitals
102
# Define
σ bond
the strongest type of covalent chemical bond that are formed by head-on overlapping between atomic orbitals
103
# Define
σ-donor ligands
A ligand that when coordinated to metal, it forms one single sigma bond
104
# Define
Reduction
reaction that involves the gaining of electrons by one of the atoms involved in the reaction
105
# Define
Thermodynamic cycle
a series of thermodynamic processes which returns a system to its initial state
106
# Definition
a type of molecular orbital (MO) that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms
Antibonding orbital
107
# Definition
the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other
Destructive interference
108
# Definition
a quantity expressing the extent to which a particular substance in solution is dissociated into ions, equal to the product of the concentrations of the respective ions divided by the concentration of the undissociated molecule
Dissociation constant
109
# Definition
the electromotive force of a cell built of two electrodes
Electrode potential
110
# Definition
a number that expresses the relationship between the amounts of products and reactants present at equilibrium in a reversible chemical reaction at a given temperature
Equilibrium constant
111
# Definition
the equilibrium constant for the formation of a complex ion from its components in solution
Formation constant
112
# Definition
A law that states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes
Hess's law
113
# Definition
every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin
Hund's rule
114
# Definition
the relative stabilities of complexes formed by transition metals as represented in a diagram
Irving-Williams series
115
# Definition
a summary of the standard electrode potential data of that element
Latimer diagram
116
# Definition
one of several theories that describe the electronic structure of coordination or complex compounds, notably transition metal complexes. It factors in the effects of π bonds as well as σ bonds
Ligand field theory
117
# Definition
the loss of electrons during a reaction by a molecule, atom or ion
Oxidation
118
# Definition
in an atom or molecule, no two electrons can have the same four electronic quantum numbers
Pauli exclusion principle
119
# Definition
a ligand that accepts electron density into it's p orbital from the metal center
π-acids
120
# Definition
a ligand with filled π-type orbitals that donates electron density to the metal center
π-bases
121
# Definition
a covalent bond formed between two neighboring atom's unbonded p-orbitals
π bond
122
# Definition
the strongest type of covalent chemical bond that are formed by head-on overlapping between atomic orbitals
σ bond
123
# Definition
A ligand that when coordinated to metal, it forms one single sigma bond
σ-donor ligands
124
# Definition
reaction that involves the gaining of electrons by one of the atoms involved in the reaction
Reduction
125
# Definition
a series of thermodynamic processes which returns a system to its initial state
Thermodynamic cycle
126
What does ligand field theory factor in that crystal field theory doesn't?
Pi bonds
127
What type of bond is this?
Electron density appears along the internuclear axis and cylindrical symmetry around the internuclear axis. That means if we rotate the orbitals around the z-axis there is no change of phase
Sigma bond
128
What type of bond is this?
A nodal plane exists along the internuclear axis, lack of cylindrical symmetry. That means if we rotate the orbitals around the z-axis there is a change of phase
Pi bond
129
In sigma donor ligands, if no pi bonding is present the energy difference between the t2g and eg orbitals corresponds to what?
Δoct
130
Sigma donors _________ electrons from lone pairs to the metal centre from either the s or p orbitals
Sigma donors **donate** electrons from lone pairs to the metal centre from either the s or p orbitals
131
What are the valence shell atomic orbitals for a first row transition metal?
3d, 4s and 4p
132
Combinations of the metals and ligand orbitals generate _____ bonding and ____ anti-bonding molecular orbitals
Combinations of the metals and ligand orbitals generate **6** bonding and **6** anti-bonding molecular orbitals
133
When there is no pi bonding present, which is the only molecular orbital that does not interact with the ligand group?
t2g orbital
134
True or False:
π-acids donate electron density to the metal centre
False
π-bases donate electron density to the metal centre
135
How does π-bases affect the molecular orbital splitting diagram from the sigma only version?
136
How does π-acids affect the molecular orbital splitting diagram from the sigma only version?
137
138
What does the formation constant represent?
It indicates the strength of binding of the ligand relative to water: if Kf is large, the incoming ligand binds more strongly than the solvent; if Kf is small, the ligand binds more weakly than water
139
140
141
What is the inverse of Kf? Why is it useful?
The inverse of each Kf is the dissociation constant, Kd , which is often preferred when we are interested in the concentration of ligand that is required to give a certain concentration of complex. Kd is the ligand concentration required to obtain 50% complexations
142
143
Why is there a consistent decrease in the stepwise formation constant as you replace ligands in a complex?
The decrease in the stepwise formation constant reflects the diminishing statistical factor as successive ligands are replaced, coupled with the fact that an increase in the number of bound ligands increases the likelihood of the reverse reaction
144
If Kfn \> Kfn+1, what has most likely occurred?
A major change in the electronic structure of the complex as more ligands are added (i.e. change in spin)
145
146
147
Explain the shape of the plot observed in the Irving Williams series. Explain the general increase left to right, the deviation from linear and the maximum at Cu
148
True or False:
The smaller the value of EO , the greater the tendency for reaction to occur left to right
False
The **greater** the value of EO , the greater the tendency for reaction to occur left to right
149
150
151
